mud pump piston assembly free sample

A wide variety of mud pump rubber piston assembly options are available to you, such as 1 year, not available.You can also choose from new, mud pump rubber piston assembly,As well as from energy & mining, construction works , and machinery repair shops. and whether mud pump rubber piston assembly is 1.5 years, 6 months, or unavailable.

TECHNICAL FIELD OF THE INVENTION The present invention relates generally to piston seals for mud pumps and more particularly to a replaceable piston seal. Still more particularly, the present invention relates to a durable polymeric piston seal constructed with very small tolerances so as to provide a precise interference fit with the corresponding liner.

Slush or mud pumps are commonly used for pumping drilling mud in connection with oil well drilling operations. Because of the need to pump the drilling mud through several thousand feet of drill pipe, such pumps typically operate at high pressures. Moreover, it is necessary for the mud to emerge from the drill bit downhole at a relatively high velocity in order to provide lubrication and cooling to the bit and to provide a vehicle for the removal of drill cuttings from the earth formation being drilled. Lastly, the pressure generated by the mud pump contributes to the total downhole pressure, which is used to prevent well blowouts.

The pistons and cylinders used for such mud pumps are susceptible to a high degree of wear during use because the drilling mud is relatively dense and has a high proportion of suspended abrasive solids. As the pump cylinder becomes worn, the small annular space between the piston and the cylinder wall increases substantially and sometimes irregularly. For these reasons, the seal design for such pumps is critical.

The high pressure abrasive environment in which the pumps must operate is especially deleterious to the seals since considerable friction forces are generated, and since the hydraulic pressures encountered during operation force the seal into the annular space between the cylinder wall and the piston. In some instances, the frictional forces may even detach the seal from the piston. In these instances, the edges of the seal can become damaged very quickly by the cutting or tearing action that occurs as a result of piston movement. Another problem with conventional mud pump seals is that they do not adequately "wipe" the

Attempts have been made to retain the seal in the piston so as to resist this frictional force. One conventional solution to this problem has been use of a metallic seal retainer which is disposed over the seal body and retained in place by snap rings. One disadvantage of this solution, however, is that the additional seal retaining element and its snap rings render the overall piston construction more expensive. A further disadvantage is that the seal is made somewhat less flexible and resilient than it would otherwise be, thus decreasing its ability to wipe the cylinder wall effectively. Another conventional solution to the sealing problem comprises including a seal retaining ring or reinforcement in the seal itself. In this case, the retaining ring or reinforcement is molded into the seal material. As with the external retaining ring, this solution decreases the flexibility of the seal and increases its cost of manufacture.

It is common to incorporate the foregoing seals into piston heads wherein the seal is permanently affixed to the piston head. This is disadvantageous because the seal tends to wear much faster than the piston head, resulting in waste and unnecessary expense when the whole piston head has to be replaced because of wear to the seal member. It is therefore desirable to provide a piston seal that is removable from the piston head and thus can be replaced without requiring replacement of the whole piston head. The nature of the mud pump operating environment makes it difficult to effectively address these issues. It is, therefore, desired to develop a new and improved replaceable seal for a reciprocating mud pump piston that overcomes the foregoing difficulties while providing better wear properties and more advantageous overall results.

BRIEF SUMMARY OF THE INVENTION The present invention comprises a new and improved replaceable seal for a reciprocating mud pump piston. The present seal does not require any external seal retaining means and is free from any incorporated seal retainer or reinforcement. The present seal is manufactured to precise specifications that minimize play between the seal, piston head and cylinder and also compensate for the slight deformation of the seal member that occurs when the seal member is demolded and cured.

Figure 3 is a cross sectional view of the sealing member of Figure 2 mounted on a piston head in a cylinder. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially to Figure 1, a typical prior-art mud pump piston assembly comprises a piston head 10 and a sealing device or seal 15 therefor slidably received in a piston cylinder 12. Piston head 10 comprises a generally cylindrical body having a flange 11 extending therefrom. Piston head 10 is typically made of steel, such as AISI 4140. Seal 15 is friction fit on piston head 10 and abuts flange 11. Seal 15 comprises an elastomeric sealing section 14 and a heel section 13. These sections are either integrally formed or bonded together. Heel section 13 is typically made from a stack of several layers of rubber- impregnated fabric, which give it a higher modulus of elasticity than the elastomeric sealing section 14. In prior art mud pumps, the heel section 13, which is stiffer than the elastomeric sealing section, resists extrusion into the gap between the cylinder and piston flange to some extent. However, heel section 13 is still forced into the gap under the influence of the hydrostatic pressure in locations where wear occurs. Reference numeral 18 designates a portion of heel section 14 that has been extruded into the gap 20 between the flange 11 and the cylinder 12. Both elastomeric sealing section 14 and heel section 13 make intimate contact with the cylinder 12. Seal 15 is held in place by a retaining ring 16 and a snap ring 17, which hold seal 15 in place and permit replacement thereof. Easy replacement of seals is a desirable feature for a mud pump, since seals typically wear out long before the other mud pump components and must be replaced in order to continue pumping operations. The direction of travel of piston 10 is shown by arrow 19. The direction of the hydrostatic pressure force exerted by the working fluid of the pump is shown by arrows 21. This force axially compresses elastomeric sealing section 14 and heel section 13 and radially expands these sections against the cylinder wall.

Referring now to Figure 3, the seal 22 of Figure 2 is shown mounted on a piston head in a cylinder. It can be seen that sealing lip 24 is compressed radially and conforms to the inside of 12. In addition, in order to enable seal 22 to be used without a reinforced heel section, piston head 10 is manufactured to extremely tight tolerances. In particular, it has been discovered that the life of seal 22 can be greatly prolonged by ensuring that play between flange 11 and cylinder 12 is minimized at the outset. Thus, the average width of the annular gap 25 between flange 11 and cylinder 12 is much smaller than in previously known devices. In this regard, it is preferred that the difference between the outside diameter of flange 11 as manufactured and the inside diameter of cylinder 12 as manufactured be less than 0.010 inches, and more preferably less than 0.008 inches. By way of example, flange 11 of a 6 inch piston is preferably about 0.002 to 0.010 inch smaller than the associated bore.

As can be seen in the Figures, the sealing lip 24 of seal 22 is preferably somewhat larger than the nominal inside diameter of the cylinder 12. Again by way of example, for a piston having a nominal diameter of six inches, sealing lip 24 preferably has a diameter of about 6.25 inches. Thus, in one preferred embodiment, diameters are as follows: for metal flange 11, df = 5.990; for cylinder 12, inside diameter idi = 6.000; for seal lip 23, ds = 6.250; and for heel 24, dh = 5.990.

Although the invention is described with particular reference to a pump piston used with slush or mud pumps, it will be recognized that certain features thereof may be used or adopted to use in other types of reciprocating pumps. Likewise it will be understood that various modification can be made to the present seal without departing from the scope of the invention. For example, the relative dimensions of various parts, the materials from which the seal is made, and other parameters can be varied, so long as the seal retains the advantages discussed herein.

This invention relates generally to piston pumps for the water well drilling industry, and more particularly to a hydraulic cylinder powered double acting duplex piston pump.

Double acting duplex piston pumps are well known and have been used in the water well drilling industry for many years. Typically they employ a crankshaft and flywheel driven in various ways, a reciprocating engine or a hydraulic motor being examples. Typically, they are heavy units with a large component of cast iron. Today"s well drilling trucks carry lengths of drilling pipe, as well as derricks, motors, pumps of various kinds, and the “mud” pump. The current double acting duplex piston pumps with crankshaft and flywheel, being very heavy, contribute significantly to the weight and space requirements of the truck. They impact the ability of a truck to meet federal highway weight restrictions. Also, the mechanical crank throw design imparts a variable speed to the mud pump piston. In such designs, the piston is either accelerating or decelerating during a large part of its design stroke. So the piston operates at its full design capacity during only a portion of the stroke. Therefore, it is an object of the present invention to provide a duplex piston pump useful as a mud pump on a water well drilling machine, but without a motor, crankshaft, flywheel, gearing, and/or belts, for a significant weight reduction.

Described briefly, according one embodiment of the present invention, a mud pump is provided with two working cylinders for pumping mud, and two sets of double-acting hydraulic driving cylinders. One set of two driving cylinders has the piston of each connected to the piston of one double-acting mud pump cylinder. The other set of two driving cylinders has the piston of each connected to the piston of the other double-acting mud pump cylinder. The connection of a set of driving cylinder pistons to the mud pump piston is through a member which allows side-by-side, or over and under parallel arrangement of the driving cylinders and mud pump cylinders, so the overall length is minimal. An electro-hydraulic control system is provided to coordinate the action of the pump driving cylinders with the mud pumping cylinders for contributing to steady flow of mud from the mud pump.

FIG. 2 is a schematic elevational view of one of the two pump assemblies of the duplex piston pump according to one embodiment of the present invention.

FIG. 3 is a schematic diagram of a system according to the illustrated embodiment and showing both of the duplex mud pump cylinders, with one of two hydraulic driving cylinders for each of the mud pump cylinders, and including an organization of hydraulic flow divider, rod position sensing, proximity-type electrical switches and associated electrical relays for solenoid-operated hydraulic fluid directing spool valves associated with the hydraulic cylinders.

FIG. 6 is an example of a flow chart relating mud pump speed to mud pump output volume capacity and hydraulic driving oil volume requirement for a pump according to the illustrated embodiment of the present invention.

FIG. 7 is a diagram showing theoretical pump driving cylinder piston performance of the two sets of mud pump driving cylinders operating according to the illustrated embodiment of the present invention.

FIG. 1 shows, schematically, a normal environment in which the mud is pumped by duplex piston pump 5 of the present invention from the chip separation tank 6 through the pump and the discharge the line 7 into the top of drill pipe 8 and down in the drill pipe and out into the well casing at the drill bit 10. The mud flows upward through the casing and back into the separation tank 6. The pump itself includes two mud pumping cylinders 1 and 2 fixed relative to a base 3 (FIGS. 5A and 5B) by mounting to four housings 4L, 4F, 4R and 4B which are fixed to the base.

As suggested above, according to the present invention, an all-hydraulic drive for the two mud-pumping pistons in cylinders 1 and 2 is achieved. For that purpose, and referring to FIG. 3, a variable volume hydraulic pump P is used. It can be set, for example, at a rate of 36 gallons per minute at 1,000 psi. A motor M can be used to drive such a pump, and such pumps and drives for them are known in the art and readily available. The pump output is fed to a flow divider D. This is not merely a device to split the flow. Instead, it has a piston inside which will shift in either direction to the extent necessary as it tries to be sure that the exact same volume flow rate is delivered at both output ports of the flow divider. An example of such a flow divider is Model MH2FA by Rexroth Worldwide Hydraulics.

Before proceeding further with this description, it is important to understand that each half of the duplex piston pump includes a double-acting mud pump cylinder and piston assembly. FIG. 2 shows one of the halves including mud pump cylinder 1. The other half, including a mud pump cylinder and associated hydraulic driving cylinders is identical. FIG. 5A shows, schematically, a rod end view of the duplex piston mud pump 5 including the mud pump cylinders 1 and 2 and associated driving cylinders of both halves.

The mud pump cylinders and their associated driving cylinders may be fixed relative to each other and mounted to the base 3 by any suitable means. The schematics of FIGS. 5A and 5B show, as an example, the four valve housings 4F, 4L,4B and 4R fixed to base 3. Except for right and left ports, each of these housings is the same as the others, and includes therein a chamber such as 41C having an opening 41A communicating with a port of a mud pump cylinder such as cylinder 1 or 2. Each chamber 41C also has two other openings. One of them is fitted with a one-way, spring loaded outlet valve such as 16 to enable mud to move from chamber 41C into the upper end of housing 4L and out through port 41D into the discharge plenum 7A. The other opening 41E of chamber 41C is fitted with a spring loaded inlet valve such as 14 communicating with the lower end of housing 4L and enabling mud entering suction inlet 6A of the mud suction manifold 6B to enter through port 41E in housing wall and into chamber 41C. The mud pump cylinders are attached to their respective valve housings in conventional manner with the ports of the cylinders communicating with the respective chambers of the housings.

Referring now to FIGS. 2 and 5A and 5B together, FIG. 2 shows schematically mud pump cylinder 1 and inlet and outlet valves 11 and 12, respectively, associated with the pump port at one end of cylinder 1, and inlet and outlet valves 14 and 16, respectively, associated with the pump port at the opposite end of cylinder 1, the rod-end of the cylinder. In practice since there would normally be only one port at each end of the cylinder, the valves would be in the housings 4L and 4F for cylinder 1. There is a packing gland 17 at the rod-end of the cylinder. In FIG. 5B the top of housing 4L is cut away to show discharge valve 16. Suction or inlet valve 14 below chamber 41C is shown larger in dashed lines to be able to see it in FIG. 5B, as it is the bottom of chamber 41C, FIG. 5A.

According to one feature of this invention, there are two hydraulic driving cylinder/piston assemblies 19 and 21 arranged in a way to drive the mud pump piston 1P in cylinder 1. As suggested above, cylinders 1, 19, and 21 are all connected relative to each other by some suitable means (brackets and/or clamps, for example) so that they are longitudinally immovable relative to one another. This is represented schematically for both sets of mud pump and driving cylinders at the valve housing 4L, 4R and associated inlet and outlet and base in FIGS. 5A and 5B, to which all of the six cylinders of both halves of the duplex pump are rigidly, but removably connected. Each of the two driving cylinder assemblies for piston 1P has a piston rod such as 19R and 21R bolted to a rod connector plate 22. Each rod may extend through the piston and exit the driving cylinder at the end opposite the plate-connected rod end, as indicated at 19S and 21S. The respective pistons 19P and 21P are affixed and sealed to the rod in a suitable way and may be of any suitable construction. Of course, the same effect may be achieved using separate colinear rods secured to opposite faces of the pistons. The piston rods 19R and 21R of the driving cylinders for mud pump cylinder 1, and rod 1R of the mud pump cylinder 1 itself, are bolted to the rod connector plate 22. Each of the rods 19R, 19S and 21R, 21S is supported at opposite ends of the respective cylinder by bearings and seals at 19B and 21B, respectively. Using double rod cylinders provides equal working area on the two sides of the piston, enabling equal oil flow and thrust capacity in both directions of piston travel. One or the other of the driving cylinder rods for mud pump cylinder 1 is associated with a set of proximity sensing switches A-1, B-1, C-1, and D-1 to operate a relay to shift a hydraulic solenoid valve spool to control hydraulic fluid to and from the set of two driving cylinders 19 and 21 to drive the mud pump 1. The same kind of arrangement is provided for mud pump cylinder 2. For each set, the driving cylinder which has the associated proximity switches, may be referred to hereinafter from time-to-time, as the control cylinder.

In this particular arrangement, only as an example of cylinder and rod size, the mud pump cylinder may be six inches in diameter with a twelve inch stroke, using the pistons of two driving cylinders of two inch diameter each to drive the one mud pump piston. A significant advantage can be achieved by making the rods of the driving cylinders larger in diameter (1.375 inches, for example) than that of the mud pump cylinder rod (1.25 inches, for example). It enables use of larger and longer wearing bearings in the driving cylinders, and enables the use of a relatively small piston rod and packing gland 17 in the mud pump cylinder, thus minimizing exposure to wear of the packing gland. The combination of the large diameter rods in the driving cylinders, fixed to a rigid rod connector plate 22 to which the mud pump cylinder rod is bolted, contributes to a very rigid structure. It avoids the necessity of a very long arrangement and long piston rod spans which would be necessary if the mud pump cylinder was driven by a single piston in a hydraulic cylinder on the same longitudinal axis. That would require a more complicated bearing arrangement to support the mud pump cylinder rod. In the present arrangement, the cylinder rod bearings are relatively close to the mud pump packing gland, helping extend the life of the gland by minimizing radial working and resulting loading of the mud pump rod on the packing gland. Also, with the present arrangement, the driving cylinder rods are in tension when the mud pump rod is in compression, which reduces the bending moment.

The proximity sensor switches A-1 through D-1 are responsive to movement of an actuator such as flange 19F on rod 19R, 19S. These switches may be normally-closed or normally-open switches as a matter of convenience in the construction of the circuitry. It should be understood, of course, that the other half of the duplex double acting pump assembly which includes cylinder 2, has driving cylinders such as 29 and 31 associated with it, and proximity switches associated with the piston rod of one (29, for example) of those driving cylinders, (shown in FIGS. 3 and 5A) in the same manner as for the assembly shown in FIG. 2. The position of the piston in cylinder 1 is preferably in a different location and/or it is moving in a different direction, from that of the piston in cylinder 2.

Referring now to FIG. 3, mud pump cylinder 1 and mud pump cylinder 2 are shown schematically, as is one cylinder of each set of two driving cylinders for each of the two mud pump cylinders 1 and 2, respectively. Since the mud pump cylinders are virtually identical and the two driving cylinders of the set for each of the mud pump cylinders are virtually identical, a description of one driving cylinder and associated controls will suffice for both.

The output from flow divider D enters the center input port of a two-position, solenoid-actuated, spring-return hydraulic valve V-1. This valve is electrically coupled to a relay switch R-1 which is bi-stable and electrically coupled to the proximity sensor switch A-1. An example of a suitable relay is No. 700-HJD32Z12 by Allen-Bradley. It is a DPDT latching relay. One switched position of this relay switch R-1 causes the solenoid to be energized to open the valve and supply pressurized oil from valve V-1 through line L-1 to the one end of cylinder 19 and likewise cylinder 21 of FIGS. 2 and 5 to drive the pistons in the direction of the arrow 23. This occurs in both driving cylinders 19 and 21, so rod 13R, being mechanically fixed to the two driving cylinder rods 19R and 21R by rod connector plate 22, is likewise driven in the direction of the arrow 23. When relay R-1 is reset by a signal from another proximity switch which can be recognized upon study of FIGS. 4A through 4D, it de-energizes the solenoid for valve V-1, enabling the spring therein to return the solenoid to position where the supply to the cylinder 19 is through line L-2, to reverse the direction of the piston in that cylinder and its companion driving cylinder, thus reversing the direction of the mud pump piston 1P. Whichever side of the piston is not pressurized at any time is enabled to dump through the valve V-1 to sump S-1. Essentially the same arrangement exists for control and drive of mud pump cylinder 2. In this instance, the proximity switches are designated A-2, B-2, C-2 and D-2. The relay switch is R-2 and the control valve is V-2 operated by a solenoid. It should be mentioned at this point, however, that while the pistons in the driving cylinders for one of the mud pump cylinders are located in the same relationship to each other as the mud pump cylinder with which they are associated, they are typically out of phase with respect to the mud pump piston and pistons of associated drive cylinders of the other mud pump cylinder. This is intentional in an effort to be sure that the flow out of the mud pump assembly 5 is as stable and constant as possible. That is the goal to which the organization of the proximity switches and associated relay switches are directed. Also with reference to FIGS. 2 and 3, it should be mentioned that the supply lines L-1 and L-2 to cylinder 19 are larger than the lines from cylinder 19 to cylinder 21. This is because the lines from valve V-1 go directly to only one of the two driving cylinders and from that point, are directed to the other driving cylinder. Thus, the supply lines L-1 and L-2 must be large enough to drive both driving cylinders 19 and 21 with essentially equal pressure and volume capacity. This is shown schematically in FIG. 2 with lines B-1 and B-2 from cylinder 19 to cylinder 21.

Referring now to FIGS. 4A through 4D, along with FIG. 3, FIG. 4A is a simplified portion of FIG. 3. It includes a driving cylinder 19 for mud pump cylinder 1, and driving cylinder 29 for mud pump cylinder 2. It also shows the proximity switches A-1 and B-1 associated with the piston rod portion 19S of cylinder 19. Similarly, proximity switches A-2 and B-2 associated with the piston rod 29S of driving cylinder 29, are shown. The position of the rod 19S relative to rod 29S is only for purposes of example, as it is not expected that the pistons of cylinders 1 and 2 will ever be positioned at the same longitudinal location relative to each other unless they are passing as one goes in one direction and the other goes in the other direction. But the purposes of the proximity switches A-1 and B-1 is to limit the travel of the piston in the two directions. Thus, either the switch A-1 or the switch B-1 can set or reset relay R-1 to cause the valve V-1 to shift and switch the high pressure from valve V-1 to either line L-1 to move the driving piston and thereby the mud pump piston 1P to the right, or apply the high pressure to line L-2 and drive the driving piston and thereby, the mud pump piston 1P to the left. Regardless of which direction the mud pump piston is moving, it will be drawing mud from the chip separation tank 6 and discharging it to the manifold connected to discharge line 7. The arrangement and operation is true regarding driving cylinder 29 and the proximity switches and relay R-2 and valve V-2 associated with that piston rod 29S.

To assure that the pistons of the two mud pump cylinders are never at either end limit of their strokes simultaneously, two additional proximity switches C-1 and D-1 (FIGS. 4B and 4D) are added. Each of these can be located about 2 inches, for example, from the proximity switches A-1 and B-1 and functions in the same way as described above with respect to switches A-1 and B-1.

The control system of FIG. 4D provides the combination of components to achieve two objectives. The first, and probably the more important, is to insure that the set of power cylinders 19 and 21 for mud pump cylinder No. 1 will cycle independently of the set of power cylinders 29 and 31 for mud pump cylinder 2, providing a 12 inch stroke for each of the mud pump cylinder rods independently of the other rod. A scheme for accomplishing this is shown generally in FIG. 4A where the sensor A-1 or the sensor B-1 can energize the latching relay R-1 at opposite ends of the piston rod stroke.

Another objective is to build a system which will insure that the piston 1P for mud pump cylinder 1 does not reach the end of its individual stroke at the same time as the piston 2P for mud pump cylinder 2. That could occur when both pistons are side-by-side and going in the same direction (FIG. 4B, for example) or when they are phased 180 degrees apart, so going in opposite directions and nearing the ends of their strokes (FIG. 4C, for example). These conditions are more complex and are addressed by the additional components shown in FIGS. 4B and 4C.

In addressing this problem, it should be recognized that the mud pump pistons could arrive at the ends of their strokes at the same time even if not necessarily together mid-stroke, but they would probably have been together at least a short distance before they reached the ends of their strokes. In FIGS. 4B and 4C and the above description, a two inch distance from the end of the stroke is mentioned and shown, but this distance could be one inch or some other suitable distance. If the two pistons are together a short distance from the end of their strokes, it is likely that they would reach the end of their strokes at essentially the same time.

Since reaching the end of the stroke simultaneously for both mud pump pistons is not desirable, the present invention reverses one of the two pistons prior to reaching the normal end of the stroke. When one piston reverses, its stroke has been limited at 10 inches. This will place the two mud pump pistons out of phase for an extended period. For this purpose, the additional proximity switches C-1 and D-1 for piston rod 19S, and C-2 and D-2 for piston rod 29S, are added, as mentioned above. For the right combination of signals, to correctly use the proximity switches C-1, C-2, D-1 and D-2, additional relays R-3, R-4, R-5 and R-6 can be used. An example is a DP/DT, a stable (non-latching) relay by Siemens, Potter & Brumfield Division.

The combination of the foregoing components for the control functions as described above and shown in FIGS. 4A, 4B and 4C, results in the control component organization of FIG. 4D which is a consolidation of the systems of FIGS. 4A, 4B and 4C, to achieve the above-mentioned goals of having the power cylinder set for mud pump cylinder 1, cycle independently of the power cylinder set for mud pump cylinder 2, and avoiding the simultaneous arrival at the end of their strokes of mud pump piston 1 and mud pump piston 2. At this point it should be understood that specific implementation of controls is not limited to the above-described organization of proximity switches, activators for them, types of valves or relays, whether electrically or pneumatically controlled, or the specific organization of an electrical, pneumatic, or optical control circuit, for example, portions of which may be solid state discrete devices, or integrated circuit organizations, as it will depend largely on the preference of and choices by a control circuit designer and well within the skill of the art of one who understands the organization and intentions and implementation described above, according to the present invention.

Initially, in the practice of the present invention according to the illustrated embodiment, it is intended that valving and control as shown in FIG. 4D and described above, or in such other scheme as may be preferred, be used so that when a constant flow of hydraulic oil is delivered into the system by the hydraulic pump P, relatively constant mud flow from the double acting duplex mud pump will be possible. With the present invention, the flow divider D (FIG. 1) is truly a flow divider, attempting to deliver the same volume at both outlet ports. To do so, it attempts to adapt to any difference in operation of one of the mud pump pistons relative to the other, by adjusting the pressure. For example, if the piston rod packing in one mud pump cylinder is tighter on the rod than on the other mud pump cylinder, the flow divider spool centering springs will tend to move the spool in a direction attempting to establish the same amount of flow to both of the hydraulic oil driving cylinders. Also, when one mud pump driving cylinder set piston reaches the end of its stroke, what would otherwise appear to be a sharp rise in pressure to be handled by the flow divider, can be tolerated by the flow divider itself so as to avoid damaging mechanical or hydraulic shock. This effect is somewhat mirrored in FIG. 7 which shows in the solid lines, the wave form of pressure available from the mud pump cylinder 1 for one stroke cycle, that being a full stroke from left to right, and a full return stroke from right to left in FIG. 3, for example. The dashed wave form represents the available pressure from mud pump cylinder No. 2. In this illustration, the discharge pressure in cylinder 1 begins a sharp rise from 0 at point A to a maximum available pressure at point M and then drops sharply beginning at point N to 0 at point R. Then it rises on the opposite side of the piston sharply at point R to the same maximum level and then drops again to 0 at point S. Meanwhile, if the pistons of the two mud pump cylinders happen to be operating at 90° phase relationship, the available pressure from the cylinder No. 2 follows the dashed line. Both of these pressure “curves” are essentially a square wave, in contrast to the somewhat sinusoidal output of a conventional, crankshaft-driven duplex piston pump. At point A, when the pistons in the driving cylinders for cylinder 1 get to the end of their stroke, the hydraulic pressure on the driving pistons rises sharply until the pistons begin moving in the opposite direction. This is because of the fact that, when the pistons of either driving cylinder set reach the end of their stroke, and the related solenoid valve is shifting to change the direction of the piston, there is no flow of oil through this valve. With a constant input flow of oil, it must be re-routed to prevent pressure build-up in the system and popping pressure relief valve, and also to prevent a volume drop in the discharge of the mud pump. The flow divider D has tolerance to enable this temporary re-routing to the driving cylinders 29 and 31. At the same time, with the additional pressure on these cylinders driving pump 2, a pressure spike may result in mud pump cylinder 2 such as shown in the dashed line at A and R and S in FIG. 7. The spike could be at other locations, depending upon the phase relationship of the cylinder set for mud pump cylinder 1 and the cylinder set for mud pump cylinder 2. Thus with a less than 100% accuracy-style flow divider D, the excess oil from one shifting solenoid valve is routed to the other (open) solenoid valve and driving cylinder set, which increases in speed and keeps the mud pump discharge constant. The oil itself becomes an accumulator and pressure relief system, operating at the exact same pressure over the full range of the operating system and produces the effect of constant velocity pistons in the mud pump.

Since these driving pistons are not driven by a crank shaft, they operate at essentially constant velocity. In other words, whereas a piston driven by a rotating crank shaft moves according to a harmonic sine wave pattern, a piston driven according to the present invention defines essentially a square wave pattern. In a conventional pump where the piston is driven by a rotating crank shaft, the inlet and outlet valves must be designed and sized to permit maximum flow, which typically occurs at the time of maximum travel of the piston, which occurs when the crank pin axis and rotational axis of the crank shaft are in a plane perpendicular to the axis of the piston. In contrast with construction according to the present invention, the inlet and outlet valves are sized to a maximum flow which is essentially constant regardless of where the piston is during its stroke, and which is only limited by the flow available from the flow divider. Therefore, as an example, where a conventional 5×6 mechanically driven pump using 5×6 valves, would handle about 150 gallons per minute, a pump according to the present invention with a 5″ diameter bore and 6″ stroke could be expected to produce on the order of 300 gallons per minute although using the same size “5×6” valves. Accordingly, the present invention provides the possibility of approximately twice the volume capacity with significantly less space and weight by virtue of the essentially constant velocity pistons, and significantly less overall length.

Referring again to FIG. 3, with the pump P delivering 36 gallons per minute, for example, the flow divider delivers approximately 18 gallons per minute through each output port, and which is delivered to the hydraulic driving cylinders. It should be understood that pumps having other capabilities in terms of volume and pressure can be employed. The 36 gallon per minute number is selected to match one combination of pump valves and suction hose size. Other combinations can be made for other sizes of suction hose, valves, and operating speeds, and are within the skill of the art. If there is no imbalance in the loads on the pistons of these sets of hydraulic cylinders, each of them can move at the rate determined by 18 gallons per minute flow into the cylinder at 1,000 psi (ignoring friction losses in the lines).

Because of the relative differences in sizes of the driving cylinders and the mud pump cylinders, and again, ignoring friction losses, the mud pump cylinders will be able to deliver 100 gallons per minute at 200 psi.

As suggested above, in the practice of the present invention, the oil of the piston pump system is used to absorb the undesirable pressure peaks of the primary hydraulic system. Resistance of the mud pump hydraulic system can offset the inertia of the traveling pistons and the piston rods when they reach the end of their stroke. The problem of moving excess oil during the time the valve spools are shifting, is addressed to avoid pressure peaks and consequent opening of the relief valves on each stroke. This problem of moving excess oil is solved by using an open system between the two sets of driving pistons. When the control valves close to change the direction of one set of pistons, the oil is free to flow to the other set of pistons which may be in the middle of their stroke operating at the same pressure. The volume of liquid lost in one mud pump cylinder is made up by the increase in the other, insuring that the mud pump discharge remains constant.

An open arrangement, however, can permit one set of pistons to develop more resistance and slow down or even stop. This would double the speed of the other piston. So the open system of the present invention is designed to permit a small amount of oil to flow in either direction, capable of eliminating the pressure peaks, but also capable of urging the two sets of pistons to travel near the same speed. This has been accomplished in the present invention by using the two sets of oil cylinders, two single-spool, two position, closed center valves V-1 and V-2, and a floating piston type of flow divider. This style divider is less than 100% accurate, permitting a small amount of oil to flow in either direction but stabilize the flow close to a 50/50 ratio. The above-mentioned Rexroth flow divider is intended to accomplish this function.

The pressurized side of a hydraulic cylinder is free to accelerate, based on the flow of oil being supplied. But the suction side of a mud pump piston has additional forces. Such piston velocity can only accelerate at a rate based on the flow of liquid moving through the suction valve. When a force is applied to increase the piston to a speed exceeding the incoming flow, increased vacuum forces or cavitation develops and the mud pump cylinder walls tend to deteriorate. Using an open-type system according to the present invention, some portion of supplied driving oil is free to move from the driving cylinder set for the starving cylinder through the flow divider to the driving cylinder set, reducing the acceleration rate and damage to the starving mud pump cylinder walls. Thus in the present invention, the primary hydraulic system can constructively interact with pressures of the secondary, mud management system.

In the water well drilling field, the application of a mud pump requires it to operate from zero to maximum pressure and zero to maximum flow as the drilling proceeds. This eliminates the opportunity to use standard accumulators and limit switches, as such devices must always be preset or designed for a given pressure. By using the open-to-atmosphere concept in the present invention, one of the two hydraulic piston sets is always working against the pressure developed by the resistance of the liquid (mud) being pumped. This liquid thus serves as an accumulator which is always working at the exact pressure required. Since the pressure is a function of the resistance of the fluid and the atmosphere, no relief valve is required.

While, the hydraulic driving cylinders are shown on top and bottom of a mud pump cylinder, other embodiments of the invention might have them beside or otherwise related to the mud pump cylinder as long as the piston rods of the hydraulic cylinders are somehow connected to the piston rod of the mud pump cylinder, so as to drive the mud pump piston. Also, some inventive aspects can be implemented with only a single hydraulic power cylinder for each mud pump cylinder, but using the accommodating flow divider and valve control system disclosed herein. While it is possible to make the cylinders the movable components, and other mixes and mechanical arrangements of rods and cylinders are possible, it is believed that making the rods the movable components simplifies the organization. In summary, the introduction of hydraulic power cylinders into a mud pump according to the present invention, eliminates the use of the complete power end (crankshaft, flywheel, etc.) of a conventional mechanically powered mud pump. Instead the cylinder power source provides a relatively constant velocity piston to move fluid at the piston"s rated flow essentially the full length of its design stroke. This permits a pump design with much smaller operating valves than would otherwise be required for the capacity required, contributing to a much smaller unit in size and weight.

Cavitation is an undesirable condition that reduces pump efficiency and leads to excessive wear and damage to pump components. Factors that can contribute to cavitation, such as fluid velocity and pressure, can sometimes be attributed to an inadequate mud system design and/or the diminishing performance of the mud pump’s feed system.

When a mud pump has entered full cavitation, rig crews and field service technicians will see the equipment shaking and hear the pump “knocking,” which typically sounds like marbles and stones being thrown around inside the equipment. However, the process of cavitation starts long before audible signs reveal themselves – hence the name “the silent killer.”

Mild cavitation begins to occur when the mud pump is starved for fluid. While the pump itself may not be making noise, damage is still being done to the internal components of the fluid end. In the early stages, cavitation can damage a pump’s module, piston and valve assembly.

The imperceptible but intense shock waves generated by cavitation travel directly from the fluid end to the pump’s power end, causing premature vibrational damage to the crosshead slides. The vibrations are then passed onto the shaft, bull gear and into the main bearings.

If not corrected, the vibrations caused by cavitation will work their way directly to critical power end components, which will result in the premature failure of the mud pump. A busted mud pump means expensive downtime and repair costs.

To stop cavitation before it starts, install and tune high-speed pressure sensors on the mud suction line set to sound an alarm if the pressure falls below 30 psi.

Although the pump may not be knocking loudly when cavitation first presents, regular inspections by a properly trained field technician may be able to detect moderate vibrations and slight knocking sounds.

Gardner Denver offers Pump University, a mobile classroom that travels to facilities and/or drilling rigs and trains rig crews on best practices for pumping equipment maintenance.

Severe cavitation will drastically decrease module life and will eventually lead to catastrophic pump failure. Along with downtime and repair costs, the failure of the drilling pump can also cause damage to the suction and discharge piping.

When a mud pump has entered full cavitation, rig crews and field service technicians will see the equipment shaking and hear the pump ‘knocking’… However, the process of cavitation starts long before audible signs reveal themselves – hence the name ‘the silent killer.’In 2017, a leading North American drilling contractor was encountering chronic mud system issues on multiple rigs. The contractor engaged in more than 25 premature module washes in one year and suffered a major power-end failure.

Gardner Denver’s engineering team spent time on the contractor’s rigs, observing the pumps during operation and surveying the mud system’s design and configuration.

The engineering team discovered that the suction systems were undersized, feed lines were too small and there was no dampening on the suction side of the pump.

Following the implementation of these recommendations, the contractor saw significant performance improvements from the drilling pumps. Consumables life was extended significantly, and module washes were reduced by nearly 85%.

Although pump age does not affect its susceptibility to cavitation, the age of the rig can. An older rig’s mud systems may not be equipped for the way pumps are run today – at maximum horsepower.

Wells are generally drilled into the ground to recover natural deposits of oil and gas, as well as other desirable materials, that are trapped in geological formations in the Earth"s crust. A well is typically drilled using a drill bit attached to the lower end of a “drill string.” Drilling fluid, or “mud,” is typically pumped down through the drill string to the drill bit. The drilling fluid lubricates and cools the drill bit, and it carries drill cuttings back to the surface in the annulus between the drill string and the borehole wall.

Another technique for measuring formation properties uses measurement tools and devices that are positioned near the drill bit in a drilling system. Measurements are made during the drilling process. A variety of downhole drilling tools, such as logging-while-drilling tools and measurement-while-drilling tools, commercially are available. “Logging-while-drilling”(“LWD”) is used to describe measuring formation properties during the drilling process. Real-time data, such as the formation pressure, allows the driller to make decisions about drilling mud weight and composition, as well as decisions about drilling rate and weight-on-bit, during the drilling process. It is noted that LWD and “measurement-while-drilling”(“MWD”) have different meanings to those having ordinary skill in the art. MWD typically refers to measuring the drill bit trajectory as well as borehole temperature and pressure, while LWD refers to measuring formation parameters, such as resistivity, porosity, permeability, and sonic velocity, among others. The distinction between LWD and MWD is not germane to the present invention, thus, this disclosure does not distinguish between the two terms.

Formation evaluation while drilling tools capable of performing various downhole formation testing typically include a small probe or pair of packers that can be extended from a drill collar to establish fluid communication between the formation and pressure sensors in the tool so that the formation fluid pressure may be measured. Some existing tools use a pump to actively draw a fluid sample out of the formation so that it may be stored in a sample chamber in the tool for later analysis. Such a pump is typically powered by a battery or by a generator in the drill string that is driven by the mud flow.

In some embodiments, the invention relates to a downhole fluid pump that includes a pump chamber and a piston disposed in the pump chamber so that the piston will move in one selected from a charge stroke and a discharge stroke when the piston is exposed to an internal pipe pressure.

In other embodiments, the invention relates to a downhole fluid pump that includes a pump chamber and a hydraulic chamber. The pump may also include a piston assembly having a first piston disposed in the pump chamber and defining a first section of the pump chamber, and a second section of the pump chamber, the piston assembly also having a second piston disposed in the hydraulic chamber and defining a first section of the hydraulic chamber and a second section of the hydraulic chamber. The first piston and the second piston may be connected by a connecting member, wherein the piston assembly is moveable with respect to the pump chamber and the hydraulic chamber. The pump may also include a valve in fluid communication with the pump chamber for selectively placing the pump chamber in fluid communication with a charge line or a discharge line, an internal pipe pressure isolation valve for selectively hydraulically coupling the hydraulic chamber to an internal pipe pressure, and an annular pressure isolation valve for selectively hydraulically coupling the hydraulic chamber to an annular pressure. In some embodiments the pump includes a spring disposed in one of the first section of the hydraulic chamber and the second section of the hydraulic chamber and positioned to exert a force on the piston assembly.

In other embodiments, the invention relates to a method of operating a fluid pump including operating the fluid pump in one selected from the group consisting of a charge stroke and a discharge stroke by applying an annular pressure to a piston, operating the fluid pump in the other of the charge stroke and the discharge stroke by applying an internal pipe pressure to the piston, and selectively repeating the applying the annular pressure to the piston and the applying the internal pipe pressure to the piston.

In some embodiments, the invention relates to a formation evaluation while drilling tool that includes a drill collar, a fluid inlet disposed in the drill collar, and a fluid pump in fluid communication with the fluid inlet. In some embodiments the fluid pump comprises a pump chamber and a first piston disposed in the pump chamber so that the piston will move in one selected from a charge stroke and a discharge stroke when the piston is exposed to an internal pipe pressure.

In some embodiments, the invention relates to a method of formation evaluation that includes establishing fluid communication between a fluid inlet in a formation evaluation while drilling tool and a formation, and drawing fluid into the tool by selectively repeating applying an annular pressure to a first side of a piston and applying an internal pipe pressure to the first side of the piston.

In one or more embodiments, the invention relates to a fluid pump that may be used in a downhole drilling environment. In some embodiments, the invention relates to a method for using a fluid pump. In one or more embodiments, the invention relates to a formation evaluation while drilling tool that includes a fluid pump. In some other embodiments, the invention relates to a method of formation evaluation while drilling. The invention will now be described with reference to the attached drawings.

The phrase “formation evaluation while drilling” refers to various sampling and testing operations that may be performed during the drilling process, such as sample collection, fluid pump out, pretests, pressure tests, fluid analysis, and resistivity tests, among others. It is noted that “formation evaluation while drilling” does not necessarily mean that the measurements are made while the drill bit is actually cutting through the formation. For example, sample collection and pump out are usually performed during brief stops in the drilling process. That is, the rotation of the drill bit is briefly stopped so that the measurements may be made. Drilling may continue once the measurements are made. Even in embodiments where measurements are only made after drilling is stopped, the measurements may still be made without having to trip the drill string.

FIG. 1 shows a drilling system 101 used to drill a well through subsurface formations. A drilling rig 103 at the surface is used to rotate a drill string 105 that includes a drill bit 107 at its lower end. As the drill bit 107 is being rotated, a “mud” pump 121 is used to pump drilling fluid, called “mud,” down (shown at arrow 104) through the drill string 105 to the drill bit 107. The mud, which is used to cool and lubricate the drill bit, exits the drill string through ports (not shown) in the drill bit 107. The mud then carries drill cuttings away from the bottom of the borehole as it flows back to the surface (shown at arrow 106) through the annulus between the drill string 105 and the formation 102. At the surface, the return mud is filtered and conveyed back to the mud pit 122 for reuse.

The lower end of the drill string 105 includes a bottom-hole assembly 110 (“BHA”) that includes the drill bit 107, as well as a number of drill collars (e.g., 112, 114) that may include various instruments, such as LWD or MWD sensors and telemetry equipment. A formation evaluation while drilling tool may, for example, be disposed in a stabilizer 114. The stabilizer 114 includes blades 115 that are in contact with the borehole wall and reduce the “wobble” of the drill bit 107. “Wobble” is the tendency of the drill string, as it rotates, to deviate from the vertical axis of the wellbore and cause the drill bit to change direction. Advantageously, a stabilizer 114 is already in contact with the borehole wall, thus, requiring less extension of a probe to establish fluid communication with the formation fluids. Those having ordinary skill in the art will realize that a formation evaluation while drilling tool could be disposed in locations other than in a stabilizer without departing from the scope of the invention.

The formation evaluation while drilling tool 601 of FIG. 2 also includes an intake subsection 608, a pump subsection 610 and sample chamber subsection 612. The intake subsection 608 is located near the center of the tool 601. The intake subsection 608, as shown, includes probes 621, 622. These probes may extend to contact the sidewall of a borehole and establish fluid communication with a formation. Other devices, such as dual packers or packer and probe combinations may be used, as will be described later with reference to FIGS. 6A and 6B.

The tool 601 includes a passage 640 that enables the downward flow of mud through the tool 601. Instruments are preferably positioned within the subsections such that the passage permits the mud to flow through the passage 640 in the tool 601. The arrangement and order of the subsections, or modules, in the tool 601 may be modified depending on the circumstances. The module arrangement is not intended to limit the invention.

FIG. 3 shows a schematic of a formation evaluation while drilling system 300 in accordance with one embodiment of the invention. The formation evaluation while drilling system 300 may form part of a formation evaluation while drilling tool, such as the formation evaluation while drilling tool 601 in FIG. 2 (i.e., the intake subsection 608, the pump subsection 610, and the sample chamber subsection 612). It is noted, that in this disclosure, a “formation evaluation while drilling tool” is used to refer to an entire tool, such as the one shown in FIG. 2. A “formation evaluation while drilling system” refers to a particular set of instruments and equipment in a tool that perform a specific type of formation evaluation. A formation evaluation while drilling tool may include more than one formation evaluation while drilling system.

The formation evaluation while drilling system 300 shown in FIG. 3 includes a probe 211, a pump 301, and sample chambers 306a, 306b, 306c. The pump 301 is in fluid communication with a fluid inlet (e.g., probe assembly 211 shown in FIG. 3) through a charge line 302, and the fluid inlet is in fluid communication with a formation F. The fluid pump 301 is also in fluid communication with a discharge line 303. In the embodiment shown, the discharge line 303 leads to the borehole discharge 311 and to a plurality of sample chambers 306a, 306b, 306cfor storing formation fluid samples. In at least one embodiment, the charge line 302 and the discharge line 303 are essentially the same flow path but separated by a three-way valve 309. The three-way valve 309 may be positioned so that the pump 301 is in fluid communication with the charge line 302 and isolated from the discharge line 303, or the three-way valve 309 may be positioned so that the pump 301 is in fluid communication with the discharge line 303 and isolated from the charge line 302.

The discharge line 303 includes a dump valve 307 that can be selectively operated to put the pump 301 in fluid communication with the borehole discharge 311. For example, the dump valve 307 may lead to a borehole discharge 311 that comprises an exit port in the side of the tool. Each of the sample chambers 306a, 306b, 306cpreferably includes a sample chamber isolation valve 305a, 305b, 305cthat may be selectively operated to put the pump 301 in fluid communication with one or more of the sample chambers 306a, 306b, 306c.

FIG. 4 shows a detailed schematic of the pump 301 in the formation evaluation while drilling system 300 in FIG. 3. The pump 301 is powered by the pressure differential between the mud pressure in the drill string (called “internal pipe pressure,” PI) and the pressure in the annulus (called “annular pressure,” PA). Referring to FIG. 2, the internal pipe pressure PIis experienced in the passage 640 inside the tool 601, and the annular pressure PAis experienced in the annulus 605 between the tool 601 and the borehole wall 603. This pressure differential (ΔP=PI−PAis created because of the pressure drop associated with pumping the mud through the drill bit at the bottom of the drill string, or through other restrictions in the drill string. The differential pressure is typically 700–1200 pounds per square inch.

Referring again to FIG. 4, the pump 301 includes a pump chamber 404 and a hydraulic chamber 410. A piston assembly 408 includes a first piston 406 positioned in the pump chamber 404, a second piston 411 positioned in the hydraulic chamber, and a connecting member 407 connecting the first and second pistons 406, 411. The first piston 406 divides the pump chamber 404 into a first section and a second section. In the embodiment shown, the first section is a fluid pumping cavity 409 and the second section is a charge cavity 417. The second piston 411 of the piston assembly 408 divides the hydraulic chamber 410 into a first section and a second section, as well. In the embodiment shown, the first section of the hydraulic chamber 410 is a spring cavity 414 and the second section is a pressure cavity 415. Seals 405, 412 are preferably provided to prevent fluid from flowing between the spring cavity 414 and the pressure cavity 415. The connecting member 407 (e.g., a rod) connects the first piston 406 and the second piston 411 of the piston assembly 408. The piston assembly 408 reciprocates, or moves back and forth, by sliding within each of the chambers 404, 410. Dashed lines 406ashow another possible position of the first piston 406 of the piston assembly 408, and dashed lines 411ashow a corresponding position for the second piston 411 of the piston assembly 408.

Before the operation of the pump 301 is described, it is important to note that, in some embodiments, the formation evaluation while drilling system (300 in FIG. 3) is “pressure balanced.” “Pressure balanced” means that all of the operative sections of the pump 301 are hydraulically coupled to the annular pressure PA. For example, the spring cavity 414 of the hydraulic chamber 410 may be filled with clean hydraulic oil that is hydraulically coupled to the annular pressure PA. The pressure cavity 415 of the hydraulic chamber 410, as will be described below, may be hydraulically coupled to either the annular pressure PAor the pipe internal pressure PI. It is the pressure differential between the pipe internal pressure PIand the annular pressure PAthat is used to operate the pump. Similarly, the charge cavity 417 of the pump section 404 may be filled with hydraulic oil that is hydraulically coupled to the annular pressure PA.

In general, a reciprocating positive displacement pump, such as the one shown in FIG. 4, will have a “charge stroke” and a “discharge stroke.” During the charge stroke, the pumping volume is increased so that fluid is drawn into the pump. During the discharge stroke, the pumping volume is decreased so that fluid is forced out of the pump. There are various arrangements of flow lines and valve positions that will enable a reciprocating positive displacement pump to pump fluid from one place to another using the charge and discharge strokes in a repeating and continuous manner.

The pump 301 shown in FIG. 4 has a charge stroke and a discharge stroke that are accomplished by moving the piston assembly 408 in different directions. When the piston moves in the charge stroke (i.e., to the right in FIG. 4), the volume of the fluid pumping cavity 409 of the pump chamber 404 will be increased, and fluid will be drawn from the flow line 402 into the fluid pumping cavity 409 of the pump chamber 404. By positioning the three-way valve 309 so that the pump chamber 404 is in fluid communication with the charge line 302 and the probe (e.g., 211 in FIG. 3), formation fluid will be drawn into the pump chamber 404 during the charge stroke.

It is noted that the embodiment shown includes a three-way valve 309, but a three-way valve is not required. For example, the junction could be controlled with a check valve and a two-way valve, or it could be controlled with two or more check valves. Additionally, a pump 301 could be devised where the charge line and the discharge line are not connected. In FIG. 4 the charge line and the discharge line essentially form part of the same section of pipe, separated by a valve. In some other embodiments, the discharge line may be separately connected to the pump 301. Those having ordinary skill in the art will be able to devise other arrangements of valves and charge and discharge lines without departing from the scope of the invention.

The piston assembly 408 is in a discharge stroke when it moves in a direction opposite to that of the charge stroke (i.e., to the left in FIG. 4). As the piston assembly 408 moves in the discharge stroke, the volume of the sample chamber 409 of the pump chamber 404 is reduced, and fluid will be pushed out of the pump chamber 404 and into the flow line 402. By positioning the three-way valve 309 so that the flow line 402 is isolated from the probe (e.g., 211 in FIG. 3) and in fluid communication with the discharge line 303, fluid may be forced from the pump 301 into the borehole or a sample chamber (e.g., 306a, 306b, 306cin FIG. 3).

In the embodiment shown in FIG. 4, a bellows chamber 423 is hydraulically coupled to the pressure cavity 415 of the hydraulic chamber 410. The bellows chamber 423 includes a bellows 421 that separates the bellows chamber 423 into a clean fluid cavity 425 and a mud cavity 426. As used herein, a “bellows” is a flexible and expansible vessel. The bellows 421 enables hydraulic chamber 410 to be hydraulically coupled to the annular pressure PAand to the internal pipe pressure PI, without being in fluid communication with either. For example, annular pressure line 431 hydraulically couples the bellows chamber 423 to the annular pressure PA, and the internal pipe pressure line 433 is hydraulically coupled to the internal pipe pressure PI. The bellows chamber 423 may be selectively hydraulically coupled to either the annular pressure PAor the internal pipe pressure PIby operation of the annular pressure isolation valve 432 and the internal pipe pressure valve 434. For example, by opening the internal pipe pressure isolation valve 434 and closing the annular pressure isolation valve 434, the bellows chamber 423 will experience the internal pipe pressure PI, and the bellows 421 will compress.

The bellows 421 is used so that the pump mechanisms will operate, as will be described, based on the pressure applied by the clean hydraulic oil in the clean fluid cavity 425. The pressure that the bellows 421 is exposed to may be transmitted to the second piston 411 through a connecting member 422 that puts the clean fluid cavity 425 in fluid communication with the pressure cavity 415 of the hydraulic chamber 410. This protects the pump mechanisms (e.g., the second piston 411 of the piston assembly 408) from the harsh and abrasive mud. Those having ordinary skill in the art will realize that the bellows