semi hydraulic pump free sample

Hydraulic systems uses fluid pressure to power a pump. That is done by pumping fluids downhole using a triplex pump designed for extremely high pressure, usually between approximately 2,000 and 5,000 psi. Hydraulic lift pumps are flexible, and are useful for wells that are producing any volume, from low to high. In general, hydraulic lifts have higher production volumes than mechanical lift pumps.

The hydraulic, reciprocating pump is at the bottom of the well. New oil is pulled from the annulus by the pump. The newly produced oil and power oil are combined, then pumped back to the surface and then to the operation’s tank battery.

Fluid is recycled to operate the wells. For a rough guideline, for every three barrels pumped into the well as power oil, you can expect to see five barrels pumped back to the surface. The extra two barrels is new production. The pump will produce oil on the triplex pump’s upstroke and on its downstroke, and its speed can be adjusted using a valve.

Some of the options are more complex. We’re going to take a look at some of the simpler options, free parallel and fixed insert pumps, as well as giving a brief overview of what a jet pump looks like.

When you decide to put a hydraulic lift on your lease, you’ll have to choose between a free parallel or a fixed insert system. The pump is similar with both options, but the choice between fixed insert and free parallel can make a big difference on which wellhead you choose, and how you decide to install the moveable pipe.

The free parallel pump using two strings of tubing, one of which is a smaller string that is strapped to the outside of the larger tubing string. Once you’ve lowered the tubing down into the well and installed the wellhead, you can simply drop the pump into the tubing.

You can then open the hydraulic valve so that the power oil or water flows down into the well, carrying the pump with it to the bottom. When the pump hits the bottom and seats properly, it will begin to function as lower as a power fluid is being pumped.

That power fluid will flow over with the produced oil and be pumped up to the surface through the smaller tube on the outside of the string. As with any pumping well, natural gas that is produced will mix with the produced oil and power fluid, and travel back to the tank battery.

An important advantage with this sort of pump is that it’s much easier to replace the pump when there’s a problem. The system is designed to allow a single person to bring the pump to the surface by turning a valve on the wellhead. The pump can be retrieved once it’s reached the surface with a few simple pieces of equipment.

Free parallel pumps can sometimes become knocked out of the proper position by solid objects, known as trash. The same valve that brings it to the surface to change can also be used to hop the pump up briefly, which will clear the trash. Returning the valve to its original position allows the pump to reseat. This is just as common with free parallel pumps as with insert pumps.

The insert pump is inserted (hence the clever name) into larger diameter tubing, usually. around 2 ⅜ inch. Attached to the top of the pump is a smaller diameter string of tubing, which is also inside the larger tube. The bottom of the pumps seats against the the tubing seating nipple. The pump is designed to use it’s own weight to hold it seated and in place. There’s a packer, so gas is returned to the surface up through the annular space, as with a mechanical pumping well. It’s then combined with the produced fluid from the wellhead, where everything enters the flow line. A pulling unit is required to retrieve the smaller tubing string and change the hydraulic pump.

Figure 3. Four different hydraulic pump designs. The fixed insert design is shown at the far left, and the free parallel design is shown third from the left. (courtesy of Trico Industries, Inc.)

As with the free parallel pump, trash can collect under the pump seating, causing production to fall or stop altogether. This can cause the column of fluid inside the larger diameter tubing to fall back into the well. A lift piston can be placed at the top of the wellhead so that power oil can be pumped under the piston. That allows the insert pump to use the same ‘hop’ technique as with a free parallel pump to clear trash and reseat the pump. This will remove the trash, and the pump will begin to operate normally again. You’ll most likely have to do this regularly while this pump is in use.

The valve on a pumping wellhead is designed so that a quarter turn of the valve handle opens the valves the correct amount to get the pump to hop up. Returning the valve to its standard setting will allow the pump and smaller diameter tubing to fall back to the bottom and where the pump will reseat.

Jet pumps are more complex. The jet action is produced using a venturi tube, which has a particular cone shape intended to narrow the flow path. The shape creates an area of low pressure by increasing flow rate. Fluid is drawn into that low pressure area.

There are a few contexts where a jet pump is going to work well. It’s common in wells offshore, where space is tight, as a single triplex unit can power several wells at once. Jet pumps can also be used with continuous coiled tubing and in horizontal completions.

A key advantage of using hydraulic production systems is that it’s easy to adjust the volume of the power fluid pumped. Hydraulic pumps can also handle a high daily production volume. Free pumps, in particular, can be replaced by one or two workers without needing a whole crew.

There are some chronic problems with hydraulic lifts systems, however. Keeping enough clean oil or water to use for power fluid can be difficult in some areas. When equipment fails, it can be time consuming to repair, with one or more wells shut in for long periods. There is also simply more equipment to monitor and maintain, as you’ll need both an additional tank for power fluid, and several tube strings in addition to power fluid lines for the hydraulic systems.

9-ft. Pneumatic Sampling – The longer 9-ft. sample head makes it easy to reach to the bottom of semi’s, and is still the quickest and most accurate method of sampling grain. No moving parts, no grain damage caused by the opening and closing of the probe doors. Our Pneumatic Stinger works on air flow, and only draws in what is forced up in the tip.

Low Pressure Hydraulics – Too much hydraulic power, especially on aluminum trailers, makes it that much easier to damage and poke holes in the trailer. Our Shuttle Probes can generate about 700 lbs. of down pressure, but from experience we have learned that 200 to 300 lbs. of down pressure more than enough to probe to the bottom of a semi hopper (see Automatic Sampling). Our hydraulic system pressure is set to a maximum of 750 psi compared to the 1200 to 1500 psi with other probes.

Self-Contained Design – All hydraulic, vacuum, and electrical components are located in the probe base. Beside being a cleaner design, it helps to protect the hoses & wiring from damage and weathering.

Hydraulic Pumps are any of a class of positive displacement machines used in fluid power applications to provide hydraulic flow to fluid-powered devices such as cylinders, rams, motors, etc. A car’s power-steering pump is one example where an engine-driven rotary-vane pump is common. The engine’s gear-type oil pump is another everyday example. Hydraulic pumps can be motor-driven, too, or manually operated. Variable displacement pumps are especially useful because they can provide infinite adjustment over their speed range with a constant input rpm.

Pumps produce flow. Pressure is resistance to flow. Whereas centrifugal pumps can run against blocked discharges without building up excess pressure, positive-displacement pumps cannot. Hydraulic pumps, like any positive-displacement pump, thus require overpressure protection generally in the form of a pressure-relief valve. Over-pressure relief is often built into the pump itself.

Hydraulic systems are used where compact power is needed and where electrical, mechanical, or pneumatic systems would become too large, too dangerous, or otherwise not up to the task. For construction equipment, hydraulic power provides the means to move heavy booms and buckets. In manufacturing, hydraulic power is used for presses and other high-force applications. At the heart of the hydraulic system is the pump itself and the selection of a correct hydraulic pump hinges on just what the hydraulic system will be expected to do.

Axial piston pumps use axially mounted pistons that reciprocate within internal cylinders to create alternating suction and discharge flow. They can be designed as variable-rate devices making them useful for controlling the speeds of hydraulic motors and cylinders. In this design, a swashplate is used to vary the depth to which each piston extends into its cylinder as the pump rotates, affecting the volume of discharge. A pressure compensator piston is used in some designs to maintain a constant discharge pressure under varying loads.

Radial piston pumps arrange a series of pistons radially around a rotor hub. The rotor, mounted eccentrically in the pump housing, forces the pistons in and out of cylinders as it rotates, which cause hydraulic fluid to be sucked into the cylinder cavity and then be discharged from it. Inlets and outlets for the pump are located in a valve in a central hub. An alternative design places inlets and outlets around the perimeter of the pump housing. Radial piston pumps can be purchased as fixed- or variable-displacement models. In the variable-displacement version, the eccentricity of the rotor in the pump housing is altered to decrease or increase the stroke of the pistons.

Rotary vane pumps use a series of rigid vanes, mounted in an eccentric rotor, which sweep along the inside wall of a housing cavity to create smaller volumes, which forces the fluid out through the discharge port. In some designs, the volume of the fluid leaving the pump can be adjusted by changing the rotational axis of the rotor with respect to the pump housing. Zero flow occurs when the rotor and housing axes coincide.

External Gear pumps rely on the counter-rotating motion of meshed external spur gears to impart motion to a fluid. They are generally fixed-displacement designs, very simple and robust. They are commonly found as close-coupled designs where the motor and pump share a common shaft and mounting. Oil travels around the periphery of the pump housing between the teeth of the gears. On the outlet side, the meshing action of the teeth decreases the volume to discharge the oil. The small amount of oil that is trapped between the re-meshing gears discharges through the bearings and back to the pump’s suction side. External gear pumps are very popular in fixed-displacement hydraulic applications as they are capable of providing very high pressures.

The internal gear pump uses the meshing action of an internal and external gear combined with a crescent-shaped sector element to create fluid flow. The axis of the external gear is offset from that of the internal gear, and as the two gears rotate, their coming out of and into mesh create suction and discharge zones. The sector serves as a barrier between suction and discharge. Another internal gear pump, the gerotor, uses meshing trochoidal gears to achieve the same suction and discharge zones without needing a sector element.

This article presented a brief summary of some of the common types of hydraulic pumps. For more information on additional topics, consult our other guides or visit the Thomas Supplier Discovery Platform to locate potential sources of supply or view details on specific products.

Hydraulic motors are rotary or mechanical actuators that operate by converting hydraulic pressure or fluid energy into torque and angular displacement.

Starting torque is the ability of a hydraulic motor to make a load start moving. The starting torque indicates the amount of torque that a hydraulic motor can develop to make a load start turning. It can be expressed as a fraction or percentage of the theoretical torque. The starting torque for piston, vane, and common gear motors is usually between 70% to 80% of the theoretical value.

Mechanical efficiency measures the effectiveness found in a machine or a mechanical system. This can be obtained from different variables and in hydraulic motors, torque usually is used. In hydraulic motors, mechanical efficiency refers to the ratio of the actual torque to be delivered to the theoretical torque.

Hydraulic motors work by converting hydraulic pressure or fluid energy into torque and angular displacement. Some components operate inside these motors to develop the required. Below is a list of the key components that are used in most hydraulic motors and their corresponding functions

In hydraulic motors, the rotor is the part that rotates after being triggered by a mechanism inside the motor. These mechanisms differ depending on the type of motor, for example in a gear-type hydraulic motor, the rotor starts rotating after meshing of the gears and fluid flow. In a vane type hydraulic motor, the rotor is triggered by the pressing of the vanes.

A driveshaft (also known as a propeller) is part of a hydraulic motor that is responsible for delivering or transferring the torque created inside the motor to the outside environment where it can be used for lifting loads and other applications. Most driveshafts are made of metals and have gear teeth on their ends.

Hydraulic motors operate by manipulation of the flow of fluid inside the motor. Directional control valves are designed to control fluid flow inside the motor. In most hydraulic and pneumatic systems these valves allow the fluids such as oil, water, air to flow from into different parts according to the control patterns and mechanisms of the system.

Hydraulic motors have a casing that protects and contains the components. They are made of different materials such as stainless steel, titanium, cast iron, low carbon steel, nickel, etc. Cases come in various shapes according to the arrangements of the components inside the motor.

A piston rod is a bar that is machined precisely and used to transmit a force created in a hydraulic or pneumatic system to a machine’s component performing the work. In hydraulic motors, piston rods are mainly used in piston-type motors to produce a turning movement.

Hydraulic motors use fluids to transmit energy from one point to another. Most hydraulic motors use water-based, petroleum-based, and synthetic fluids. The widely used is petroleum-based which is also known as mineral-based. This mineral-based product comes in many forms depending on the additives used and the quality of the crude oil used. Common fluid additives include anti-corrosion agents, demulsifiers, extreme pressure agents, rust, oxidation inhibitors, and defoamants.

Bearings are mechanical components that enable the rotation of parts by reducing friction and holding the load. In hydraulic motors the bearing is mainly used on the driveshaft to enable smooth and efficient rotation of the shaft. Many types of bearings are used on rotating shafts and the choice of one depends on many factors such as shaft speed, amount of load, the direction of the load, type of fluid used, etc.

It is important to know and understand how hydraulic pumps and motors differ from each other. Hydraulic pumps and motors operate similarly to each other to such an extent that some people do not know the differences. Some use the word pump when in effect they are talking about a motor and vice versa.

Hydraulic motors can operate in either direction. Hydraulic motors have mechanisms that allow them to rotate in either direction (negative or positive rotation) are required to have positive and negative rotation, which is why their internal structure is symmetrical, and hydraulic pumps generally rotate in a single direction, so that requirement is not necessary.

For example, in a vane motor, the blades can only be arranged in a radial manner. It can not be inclined like a vane pump, because this will cause the blades to be broken when reversing. The distribution plate in the axial plunger motor is supposed to have a symmetrical design, in that case, the axial plunger of the pump is not; the gear motor should have a separate leakage tube.

Hydraulic pumps are mainly used when they are connected with a prime mover and motors are connected with loads. The pump in essence has no radial loads such as pulleys, sprockets, belts which can be found in hydraulic motors.

High-speed low torque (HSLT) hydraulic motors are sometimes referred to as high revs per minute (RPM) motors are designed to operate at high speeds ranging from 1 000 rpm to 14 000 rpm. They are used when the load is light because they have a low torque range. They can be used for applications in the utility, earthmoving, forestry, material handling etc.

In this gear type, the hydraulic motor is made of two gears which are called the driven gear and the idle gear. The driven gear is connected to the output shaft usually by means of a key. Inside the motor is high pressure oil which flows into the sides around the gear tips and flows into the motor housing exiting through the outlet port. In the process, the gears mesh, and this will not allow oil coming from the outlet to flow back into the inlet side.

A small amount of this oil is used for lubrication of the gears. This oil is bled through the bearings (hydrodynamic), and the oil enters through the pressure side of the gears. The spur gears are popularly used in these types of hydraulic motors. If the gears are not manufactured to standards, they may become subject to vibration and may be noisy during the operation of the motor.

Internal gear motors have similar features and characteristics to external gear motors. The smooth operation of the gears characterizes the motors as compared to external gears where they are subjected to vibration causing noisy situations. They have one external gear that is used to mesh with the circumference of a larger gear. Internal gears are found in two versions namely the gerotor motor (mainly used in mobile systems and hydraulic technologies) and the gerotor motor.

In these gear motors a crescent vane is used to separate the discharge volume from the inlet volume between the two gears. When the hydraulic fluid enters through the inlet volume it causes the pressure to increase causing the volume to expand and this results in the gears rotating. The fluid will be forced out as the gears continue to rotate.

Hydraulic motors operate by creating an imbalance due to pressure which results in the rotation of the shaft. In vane motors, this imbalance is a result of the difference when the vane area is exposed to hydraulic pressure. Vane motors have a hydraulic balance which prevents the rotor from sideloading the shaft. The pressure difference develops the torque as the oil from the pump is forced to go through the motor.

Vane motors are usually made of a cartridge configuration of a motor housing. Their design is like that of a vane pump. They are characterized by two-port plates that separate the outlet and inlet ports as they put in between them the cam and rotor ring. Inside the cylindrical case of a vane motor is a ring mounted. This ring is made up of radial slots where there are sliding vanes. The vanes operate by pressing inside, against the wall of the cylindrical case. The ring rotates when the vanes are spring forced against the wall due to centrifugal force.

The radial-piston type hydraulic motor operates by transforming the energy created by the fluid pressure into mechanical energy (rotation). There is a directional valve, which is a fixed and central part of the configuration, it has two lines for fluid flow where one is for draining and another for fluid intake. The rotor is for turning in the directional valve which is fitted with radial bores. This will cause the free-floating pistons to operate.

When the hydraulic fluid, that is pressurized by the pump, gets into the bores it presses the pistons against the stator usually for half a revolution. In the following half revolution, the fluid is delivered into the draining line connected to the directional valve. If the motor is operating under pressure loading on the motor piston, the stator will exert stress on the piston, and this will make the pistons and the rotor rotate. When this happens the output shaft of the motor is driven. Most of these systems are fitted with rollers which reduce the losses caused by piston friction on the track.

Axial piston-type hydraulic motors are also known as barrel motors. In these motors the plate of the drive shaft is positioned at an angle with respect to the barrel of the motor, the intake of fluid in the cylinders results in the movement of the pistons, causing the drive to rotate. In each cylinder, there is 1 phase of output and of intake per rotation. The piston operates when it is applied to the inclined plate with a force proportional to the pressure. This force reduces the angle and creates a force that makes the plate rotate.

When choosing a hydraulic motor to use there are factors that one needs to consider when designing an efficient system. The motor used should match the system requirement and if it does not this might affect the whole system. Below is a list of some of the factors and questions to consider.

There are many applications that hydraulic motors can be used for. These motors are made of different materials meaning they respond differently to operating conditions. Some are strong enough to withstand vibrations and harsh conditions and these are mainly used for industrial applications.

Before one can choose a type of motor to use, they need to gather installation information as well. This is because other motor types require a lot of expertise and are complicated to install. It is essential to talk with professionals about the other costs that are involved before purchasing a hydraulic motor.

A closed-loop in a hydraulic system is also known as a hydrostatic drive and is commonly found in mobile systems and industrial machines such as conveyors. In a closed-loop, the fluid flows directly from the pump to the motor and then returns to the pump without entering a reservoir. The fluid flow determined the speed of the motor. In an open loop, the fluid flows from the motor to the pump through a reservoir. Before choosing the right motor for the system it is essential to understand the loop that will operate in the specific hydraulic system.

Hydraulic motors play a vital role in the engineering and automation of many systems in our everyday lives. Although some of them are complex, most of these motors use simple operating principles which are easy to understand and are user-friendly.

Automatic transmissions ask a lot of the oil. Not only does the oil lubricate and clean internal parts, but it also functions as a hydraulic oil to operate various components.LEARN MORE

Things like restrictions and blockages can impede the flow of fluid to your pump. which could contribute to poor fluid flow. Air leak in suction line. Air present in the pump at startup. Insufficient supply of oil in pump. Clogged or dirty fluid filters. Clogged inlet lines or hoses. Blocked reservoir breather vent. Low oil in the reservoir

Now that we’ve ensured that the directional control is not reversed, it’s time to check that the drive motor itself is turning in the right direction. Sometimes incorrect installation leads to mismatched pipe routings between control valves and motors, which can reverse the direction of flow. Check to see that the motor is turning the pump in the right direction and if not - look at your piping.

Check to ensure that your pump drive motor is turning over and is developing the required speed and torque. In some cases, misalignment can cause binding of the drive shaft, which can prevent the motor from turning. If this is the case, correct the misalignment and inspect the motor for damage. If required, overhaul or replace motor.

Check to ensure the pump to motor coupling is undamaged. A sheared pump coupling is an obvious cause of failure, however the location of some pumps within hydraulic systems makes this difficult to check so it may go overlooked

It is possible that the entire flow could be passing over the relief valve, preventing the pressure from developing. Check that the relief valve is adjusted properly for the pump specifications and the application.

Seized bearings, or pump shafts and other internal damage may prevent the pump from operating all together. If everything else checks out, uncouple the pump and motor and check to see that the pump shaft is able to turn. If not, overhaul or replace the pump.

If your pump is having problems developing sufficient power, following this checklist will help you to pinpoint the problem. In some cases you may find a simple solution is the answer. If your pump is exhibiting any other issues such as noise problems, heat problems or flow problems, you may need to do some more investigation to address the root cause of your pump problem. To help, we’ve created a downloadable troubleshooting guide containing more information about each of these issues. So that you can keep your system up and running and avoid unplanned downtime. Download it here.

Check that the pump shaft is rotating. Even though coupling guards and C-face mounts can make this difficult to confirm, it is important to establish if your pump shaft is rotating. If it isn’t, this could be an indication of a more severe issue, and this should be investigated immediately.

Check the oil level. This one tends to be the more obvious check, as it is often one of the only factors inspected before the pump is changed. The oil level should be three inches above the pump suction. Otherwise, a vortex can form in the reservoir, allowing air into the pump.

What does the pump sound like when it is operating normally? Vane pumps generally are quieter than piston and gear pumps. If the pump has a high-pitched whining sound, it most likely is cavitating. If it has a knocking sound, like marbles rattling around, then aeration is the likely cause.

Cavitation is the formation and collapse of air cavities in the liquid. When the pump cannot get the total volume of oil it needs, cavitation occurs. Hydraulic oil contains approximately nine percent dissolved air. When the pump does not receive adequate oil volume at its suction port, high vacuum pressure occurs.

This dissolved air is pulled out of the oil on the suction side and then collapses or implodes on the pressure side. The implosions produce a very steady, high-pitched sound. As the air bubbles collapse, the inside of the pump is damaged.

While cavitation is a devastating development, with proper preventative maintenance practices and a quality monitoring system, early detection and deterrence remain attainable goals. UE System’s UltraTrak 850S CD pump cavitation sensor is a Smart Analog Sensor designed and optimized to detect cavitation on pumps earlier by measuring the ultrasound produced as cavitation starts to develop early-onset bubbles in the pump. By continuously monitoring the impact caused by cavitation, the system provides a simple, single value to trend and alert when cavitation is occurring.

The oil viscosity is too high. Low oil temperature increases the oil viscosity, making it harder for the oil to reach the pump. Most hydraulic systems should not be started with the oil any colder than 40°F and should not be put under load until the oil is at least 70°F.

Many reservoirs do not have heaters, particularly in the South. Even when heaters are available, they are often disconnected. While the damage may not be immediate, if a pump is continually started up when the oil is too cold, the pump will fail prematurely.

The suction filter or strainer is contaminated. A strainer is typically 74 or 149 microns in size and is used to keep “large” particles out of the pump. The strainer may be located inside or outside the reservoir. Strainers located inside the reservoir are out of sight and out of mind. Many times, maintenance personnel are not even aware that there is a strainer in the reservoir.

The suction strainer should be removed from the line or reservoir and cleaned a minimum of once a year. Years ago, a plant sought out help to troubleshoot a system that had already had five pumps changed within a single week. Upon closer inspection, it was discovered that the breather cap was missing, allowing dirty air to flow directly into the reservoir.

A check of the hydraulic schematic showed a strainer in the suction line inside the tank. When the strainer was removed, a shop rag was found wrapped around the screen mesh. Apparently, someone had used the rag to plug the breather cap opening, and it had then fallen into the tank. Contamination can come from a variety of different sources, so it pays to be vigilant and responsible with our practices and reliability measures.

The electric motor is driving the hydraulic pump at a speed that is higher than the pump’s rating. All pumps have a recommended maximum drive speed. If the speed is too high, a higher volume of oil will be needed at the suction port.

Due to the size of the suction port, adequate oil cannot fill the suction cavity in the pump, resulting in cavitation. Although this rarely happens, some pumps are rated at a maximum drive speed of 1,200 revolutions per minute (RPM), while others have a maximum speed of 3,600 RPM. The drive speed should be checked any time a pump is replaced with a different brand or model.

Every one of these devastating causes of cavitation threatens to cause major, irreversible damage to your equipment. Therefore, it’s not only critical to have proper, proactive practices in place, but also a monitoring system that can continuously protect your valuable assets, such as UE System’s UltraTrak 850S CD pump cavitation senor. These sensors regularly monitor the health of your pumps and alert you immediately if cavitation symptoms are present, allowing you to take corrective action before it’s too late.

Aeration is sometimes known as pseudo cavitation because air is entering the pump suction cavity. However, the causes of aeration are entirely different than that of cavitation. While cavitation pulls air out of the oil, aeration is the result of outside air entering the pump’s suction line.

Several factors can cause aeration, including an air leak in the suction line. This could be in the form of a loose connection, a cracked line, or an improper fitting seal. One method of finding the leak is to squirt oil around the suction line fittings. The fluid will be momentarily drawn into the suction line, and the knocking sound inside the pump will stop for a short period of time once the airflow path is found.

A bad shaft seal can also cause aeration if the system is supplied by one or more fixed displacement pumps. Oil that bypasses inside a fixed displacement pump is ported back to the suction port. If the shaft seal is worn or damaged, air can flow through the seal and into the pump’s suction cavity.

As mentioned previously, if the oil level is too low, oil can enter the suction line and flow into the pump. Therefore, always check the oil level with all cylinders in the retracted position.

If a new pump is installed and pressure will not build, the shaft may be rotating in the wrong direction. Some gear pumps can be rotated in either direction, but most have an arrow on the housing indicating the direction of rotation, as depicted in Figure 2.

Pump rotation should always be viewed from the shaft end. If the pump is rotated in the wrong direction, adequate fluid will not fill the suction port due to the pump’s internal design.

A fixed displacement pump delivers a constant volume of oil for a given shaft speed. A relief valve must be included downstream of the pump to limit the maximum pressure in the system.

After the visual and sound checks are made, the next step is to determine whether you have a volume or pressure problem. If the pressure will not build to the desired level, isolate the pump and relief valve from the system. This can be done by closing a valve, plugging the line downstream, or blocking the relief valve. If the pressure builds when this is done, there is a component downstream of the isolation point that is bypassing. If the pressure does not build up, the pump or relief valve is bad.

If the system is operating at a slower speed, a volume problem exists. Pumps wear over time, which results in less oil being delivered. While a flow meter can be installed in the pump’s outlet line, this is not always practical, as the proper fittings and adapters may not be available. To determine if the pump is badly worn and bypassing, first check the current to the electric motor. If possible, this test should be made when the pump is new to establish a reference. Electric motor horsepower is relative to the hydraulic horsepower required by the system.

For example, if a 50-GPM pump is used and the maximum pressure is 1,500 psi, a 50-hp motor will be required. If the pump is delivering less oil than when it was new, the current to drive the pump will drop. A 230-volt, 50-hp motor has an average full load rating of 130 amps. If the amperage is considerably lower, the pump is most likely bypassing and should be changed.

Figure 4.To isolate a fixed displacement pump and relief valve from the system, close a valve or plug the line downstream (left). If pressure builds, a component downstream of the isolation point is bypassing (right).

The most common type of variable displacement pump is the pressure-compensating design. The compensator setting limits the maximum pressure at the pump’s outlet port. The pump should be isolated as described for the fixed displacement pump.

If pressure does not build up, the relief valve or pump compensator may be bad. Prior to checking either component, perform the necessary lockout procedures and verify that the pressure at the outlet port is zero psi. The relief valve and compensator can then be taken apart and checked for contamination, wear, and broken springs.

Install a flow meter in the case drain line and check the flow rate. Most variable displacement pumps bypass one to three percent of the maximum pump volume through the case drain line. If the flow rate reaches 10 percent, the pump should be changed. Permanently installing a flow meter in the case drain line is an excellent reliability and troubleshooting tool.

Ensure the compensator is 200 psi above the maximum load pressure. If set too low, the compensator spool will shift and start reducing the pump volume when the system is calling for maximum volume.

Performing these recommended tests should help you make good decisions about the condition of your pumps or the cause of pump failures. If you change a pump, have a reason for changing it. Don’t just do it because you have a spare one in stock.

Conduct a reliability assessment on each of your hydraulic systems so when an issue occurs, you will have current pressure and temperature readings to consult.

Al Smiley is the president of GPM Hydraulic Consulting Inc., located in Monroe, Georgia. Since 1994, GPM has provided hydraulic training, consulting and reliability assessments to companies in t...

A gear pump is a type of positive displacement (PD) pump. Gear pumps use the actions of rotating cogs or gears to transfer fluids. The rotating gears develop a liquid seal with the pump casing and create a vacuum at the pump inlet. Fluid, drawn into the pump, is enclosed within the cavities of the rotating gears and transferred to the discharge. A gear pump delivers a smooth pulse-free flow proportional to the rotational speed of its gears.

There are two basic designs of gear pump: internal and external (Figure 1). An internal gear pump has two interlocking gears of different sizes with one rotating inside the other. An external gear pump consists of two identical, interlocking gears supported by separate shafts. Generally, one gear is driven by a motor and this drives the other gear (the idler). In some cases, both shafts may be driven by motors. The shafts are supported by bearings on each side of the casing.

As the gears come out of mesh on the inlet side of the pump, they create an expanded volume. Liquid flows into the cavities and is trapped by the gear teeth as the gears continue to rotate against the pump casing.

No fluid is transferred back through the centre, between the gears, because they are interlocked. Close tolerances between the gears and the casing allow the pump to develop suction at the inlet and prevent fluid from leaking back from the discharge side (although leakage is more likely with low viscosity liquids).

External gear pump designs can utilise spur, helical or herringbone gears (Figure 3). A helical gear design can reduce pump noise and vibration because the teeth engage and disengage gradually throughout the rotation. However, it is important to balance axial forces resulting from the helical gear teeth and this can be achieved by mounting two sets of ‘mirrored’ helical gears together or by using a v-shaped, herringbone pattern. With this design, the axial forces produced by each half of the gear cancel out. Spur gears have the advantage that they can be run at very high speed and are easier to manufacture.

Gear pumps are compact and simple with a limited number of moving parts. They are unable to match the pressure generated by reciprocating pumps or the flow rates of centrifugal pumps but offer higher pressures and throughputs than vane or lobe pumps. External gear pumps are particularly suited for pumping water, polymers, fuels and chemical additives. Small external gear pumps usually operate at up to 3500 rpm and larger models, with helical or herringbone gears, can operate at speeds up to 700 rpm. External gear pumps have close tolerances and shaft support on both sides of the gears. This allows them to run at up to 7250 psi (500 bar), making them well suited for use in hydraulic power applications.

Since output is directly proportional to speed and is a smooth pulse-free flow, external gear pumps are commonly used for metering and blending operations as the metering is continuous and the output is easy to monitor. The low internal volume provides for a reliable measure of liquid passing through a pump and hence accurate flow control. They are also used extensively in engines and gearboxes to circulate lubrication oil. External gear pumps can also be used in hydraulic power applications, typically in vehicles, lifting machinery and mobile plant equipment. Driving a gear pump in reverse, using oil pumped from elsewhere in a system (normally by a tandem pump in the engine), creates a motor. This is particularly useful to provide power in areas where electrical equipment is bulky, costly or inconvenient. Tractors, for example, rely on engine-driven external gear pumps to power their services.

External gear pumps can be engineered to handle aggressive liquids. While they are commonly made from cast iron or stainless steel, new alloys and composites allow the pumps to handle corrosive liquids such as sulphuric acid, sodium hypochlorite, ferric chloride and sodium hydroxide.

External gear pumps are self-priming and can dry-lift although their priming characteristics improve if the gears are wetted. The gears need to be lubricated by the pumped fluid and should not be run dry for prolonged periods. Some gear pump designs can be run in either direction so the same pump can be used to load and unload a vessel, for example.

The close tolerances between the gears and casing mean that these types of pump are susceptible to wear particularly when used with abrasive fluids or feeds containing entrained solids. External gear pumps have four bearings in the pumped medium, and tight tolerances, so are less suited to handling abrasive fluids. For these applications, internal gear pumps are more robust having only one bearing (sometimes two) running in the fluid. A gear pump should always have a strainer installed on the suction side to protect it from large, potentially damaging, solids.

Generally, if the pump is expected to handle abrasive solids it is advisable to select a pump with a higher capacity so it can be operated at lower speeds to reduce wear. However, it should be borne in mind that the volumetric efficiency of a gear pump is reduced at lower speeds and flow rates. A gear pump should not be operated too far from its recommended speed.

For high temperature applications, it is important to ensure that the operating temperature range is compatible with the pump specification. Thermal expansion of the casing and gears reduces clearances within a pump and this can also lead to increased wear, and in extreme cases, pump failure.

Despite the best precautions, gear pumps generally succumb to wear of the gears, casing and bearings over time. As clearances increase, there is a gradual reduction in efficiency and increase in flow slip: leakage of the pumped fluid from the discharge back to the suction side. Flow slip is proportional to the cube of the clearances between the cog teeth and casing so, in practice, wear has a small effect until a critical point is reached, from which performance degrades rapidly.

Gear pumps continue to pump against a back pressure and, if subjected to a downstream blockage will continue to pressurise the system until the pump, pipework or other equipment fails. Although most gear pumps are equipped with relief valves for this reason, it is always advisable to fit relief valves elsewhere in the system to protect downstream equipment.

The high speeds and tight clearances of external gear pumps make them unsuitable for shear-sensitive liquids such as foodstuffs, paint and soaps. Internal gear pumps, operating at lower speed, are generally preferred for these applications.

External gear pumps are commonly used for pumping water, light oils, chemical additives, resins or solvents. They are preferred in any application where accurate dosing is required such as fuels, polymers or chemical additives. The output of a gear pump is not greatly affected by pressure so they also tend to be preferred in any situation where the supply is irregular.

An external gear pump moves a fluid by repeatedly enclosing a fixed volume within interlocking gears, transferring it mechanically to deliver a smooth pulse-free flow proportional to the rotational speed of its gears.

External gear pumps are commonly used for pumping water, light oils, chemical additives, resins or solvents. They are preferred in applications where accurate dosing or high pressure output is required. External gear pumps are capable of sustaining high pressures. The tight tolerances, multiple bearings and high speed operation make them less suited to high viscosity fluids or any abrasive medium or feed with entrained solids.