screw type hydraulic pump free sample

BKD series single screw pump, V for vertical pump, H for hopper pump, horizontal ellipsis not standard; Z is a directly connected structure, bearing structure is not standard.

One or Two Pairs of Screws, which operate without being in contact with each other, ensure a constant flow, pulsation-free, together with a high suction lift capability with very low NPSH values.

The Screws Pair rotates inside the Pump Enclosure, creating several separate chambers and pushing the fluid trapped inside in accordance with the progression of the screws pitch.

The flow rate is particularly uniform and pulsation-free, and the pumped fluid flows in an axial direction (not circumferentially, as it happens in the centrifugal pumps).

Thanks to the absence of pulsations, to the low flow internal velocities, to the minimization of the centrifugal movements and to the absence of contact between the screw rotors, the pumped product does not suffer of changes of volume, texture, aspect and properties.

Thanks to the low inertia of the rotating parts, the Screw Pumps can work at rotating speeds higher than other Positive Displacement Pumps of equivalent volume chambers.

Very well suited to pump very viscous liquids, sensitive to shear forces and turbulences thanks to the low Internal velocities given by the screws movement.

Capable of Operating at High Angular Speeds thanks to the screws low inertia, allowing a high range of flow rates if the pumps are driven by a Variable Speed Drive or by an Inverter

The Fluid enters the Pump Suction Flange and, because of frictions and hydraulic effects (changes of flow, turbulences etc.), the hydrostatic pressure of the fluid drops down.

If the Fluid Pressure in a major cavity of the pump drops down the vapor pressure, then the liquid will vaporize (formation of vapor/gas bubbles in the liquid).

If the Pressure in any part of the Pump Chamber falls below the Fluid Vapour Pressure, the Fluid will vaporize (formation of bubbles of gas/vapour inside the liquid).

Inside or downstream of the pump, because of the pumping effect, the fluid pressure will be over the Vapour Pressure again, and the gas bubble will implode suddenly and become liquid again. This implosion is very fast and a multitude of collapsing bubbles generates a noise similar to Cracking or Small stones passing inside the piping.

Screw pumps belong to the family of dry compressing gas transfer pumps. (Learn more about the origins of dry pumps here) They are positive-displacement pumps that use two screw shaped intermeshing rotors to move gas along the screw’s axis. They are frequently used in industrial vacuum applications, often in combination with roots blowers and as oil-free roughing pumps in high and ultrahigh vacuum systems.

Screw pumps operate using two counter-rotating screw rotors which are engineered so that they rotate “towards each other”. This traps the gas in the space between the “screws” of their rotors. As the screws rotate, this trapped volume decreases which not only compresses the gas but moves it towards the exhaust.

In the first cases (Fig 2, 3), mechanical bearings support the rotors at both ends. The cantilever design (Fig.4) solution supports the rotors at the high pressure end and the rotors can be cooled internally. A motor drives the two rotors via a gear. Gear and the bearings are lubricated but separated from the pumping mechanism ("vacuum generator") via shaft seals or labyrinth seals, thus the compression is oil-free. The rotors have no mechanical contact between each other and the pump housing, resulting in zero mechanical wear. To keep the installed electrical power low, modern pumps are driven by an electronic frequency converter and rotate slower at pressures ranges near atmospheric pressure. Some versions use so-called blow-off valves instead to keep the rotating speed constant also at high pressures. Cooling is normally done by water.

Screw pumps can reach ultimate pressures of ~1e-3 mbar. The operating pressure range is 103 to10-2 mbar. Various sizes with pumping speed ~ 60 - 1200 m³/h are available. The pumping speed in the vacuum range < 10 - 50 mbar can be enhanced by placing a roots blower on top. These combinations, often in one single pump housing, are available up to 9000 m³/h

Screw pumps have become the standard solution in almost every industrial vacuum process. Vacuum furnaces for brazing or sintering, metallurgical systems, even steel degassing plants use the advantage of dust resistance and long service intervals. In food processing, food drying, food packaging and even freeze dryers tend to use oil free screw pumps to avoid the contamination of pump oil by water or debris from the process. Large scale coating like architectural glass coaters use screw pumps as roughing pumps for the high vacuum pumps. Screw pumps also are the ideal choice for regeneration of larger cyropumps.

Screw pumps are today also the standard primary pump in large scale scientific experiments such as big storage rings, gravitational wave detectors or space simulation chambers. One example is the KATRIN experiment which is the world"s largest Ultra High Vacuum (UHV) chamber, where the initial evacuation is done by screw pumps.

Discover more about the most common types of vacuum pumps, their applications, process conditions and operating principles bydownloading our eBooktoday:

Pre-assembled progressive cavity pump kit with progressive cavity  pump VISCOPOWER F 570 and planetary gear for food and pharma to pump thin to medium viscous media up ...

Pre-assembled progressive cavity pump kit with progressive cavity pump VISCOPOWER F 570 and planetary gear for industrial applications to pump thin to ...

The new generation of FLUX progressive cavity pump VISCOPOWER F 570 for Industry & Hygienic with planetary gear is suitable to pump thin to medium viscous media. The positive displacement ...

The MP1 is a double suction, twin screw pump designed for continuous service in high viscosity applications where multiple phases are expected. With its unique double case design, it acts inherently as ...

Reduce maintenance and sanitisation time at your facility with the SaniForce Drum Pump, designed for easy cleaning with quick tri-clamp connections, minimal moving parts and easy transferability.

This specialist machine can be used for all premixed dry mortar and site-made mixes. The Putzmeister SP 11 LMR worm pump offers lasting value, thanks to its lightweight yet robust plastic hood, for example, which can ...

... demand for Water Screw Pumps has increased again after a temporary slump in the 1990s. In spring 2014, RONCUZZI set a new record producing three Archimedean screws having a diameter ...

... beared in oil, drawing the material from above into the pump housing. The material is chopped up both by the screw and by the built-in cast-iron or stainless-steel chopper installed in the pump ...

... 797PCP-2K Series pumps precisely meter accurate ratios of part A and part B materials through static mixers for highly repeatable dispensing with fluid deposit accuracy at +/- 1%.

Viking’s LVP Series™ stainless steel vane pumps is an industrial design which provides smooth flow at pressures higher than typically seen in a vane pump. ...

... progressing cavity pump is especially interesting where pumps are installed in wear intensive applications requiring more service and maintenance work. Up to 66 percent of working time ...

... abrasive, with the NEMO® BY progressing cavity pump even difficult substances can be conveyed gently and with low pulsation, regardless of fluctuations in pressure and viscosity. In addition, the progressing ...

... progressing cavity pumps are used in demanding applications for continuous, pressure-stable, gentle and low-pulsation conveyance as well as dosing in proportion to speed in nearly every branch of industry ...

ViscoTec dispenser 3VMP18, as a volumetric dispensing pump for larger volumes, ensures smooth and reliable product supplying of abrasive, high-filled or shear sensitive material - with a repeatability of +/- 1 %!

ViscoTec dispenser 3VMP18, as a volumetric dispensing pump for larger volumes, ensures smooth and reliable product supplying of abrasive, high-filled or shear sensitive material - with a repeatability of +/- 1 %!

Compact C Pump delivers reliable performance to the maximum duty requirements of your application in a compact package. Features include suction lift capability up to 28 feet, positive ...

For nearly 50 years, versatile L-Frame pumps have stood the test of time meeting thousands of application challenges with performance-enhancing, cost-saving features.

Packo twin screw pumps offer maximum flexibility in terms of the type of application, as well as the nature of the medium to be pumped. Exceptionally ...

Packo twin screw pumps offer maximum flexibility in terms of the type of application, as well as the nature of the medium to be pumped. Exceptionally good hygiene and cleanability make ...

Packo twin screw pumps offer maximum flexibility in terms of the type of application, as well as the nature of the medium to be pumped. Exceptionally good hygiene and cleanability make ...

... accessory. Quick and easy disconnection of the drive from the pump station can be achieved with the clip lock, resulting in being able to use one drive for filling at numerous stationary pump stations. ...

... damage or pulsing when feeding the medium, the single screw pump is utilized widely in all fields to feed mediums. The gauging aim can be changed by adjusting the rotation speed.

When developing this exceptional pump, we intended to set new standards in double-screw technology. We started by rethinking functional principles from the ground up and eliminated previously known deficiencies ...

The screw pump structure is similar to a screw, and the owl spindle construction is similar to an Archimedes screw. The spindle of the pump is responsible for the action of the pump. Over the years, this pump has observed. This pump is a potential device intended for raising the pump pressure. The maintenance of this pump is less. Like other pumps, these pumps are also taking the mechanical from a motor. The different parts in these pumps can be made with different materials like casing is made with cast iron, screw shafts are made with high-grade carbon steel, and bearing is made with high-speed steels. This article discusses an overview of the screw pump.

This is a positive displacement pump which can be built with several screws. These screws are intermeshed to pressure liquids & move them within a system. The screws in the pump take the fluids and push out from another surface while growing its pressure.

The construction of this pump is consistent as well as simple in making. It has three screws spindles where one screw is drivers and remaining two screws are driven. These screws have a good clearance among them and it is responsible for the fluid pumping action. The liquid supply to the screw is given throughout the motor.

These pumps have a casing with inlet as well as an outlet, where the inlet is always selected at the bottom of the pump and outlet is selected at the upper side of the pump. All these can be observed in construction. It has a relief valve mounted at the outlet end.

The working of the screw pump is when this pump is pushing thick fluid, and then the screws can be connected strongly with no permission, as the faces are being lubricated like the liquid is pumped. When the fluid is pumping, then these parts cannot get in touch with each other, also fast wear on the elements will take place. Due to this reason, a three screw pump should not be utilized for multi-phase or water service.

In triple screw pumps, only shaft seals are required over the rotor driving. Additional rotors include bearings, which are covered within the pumping hall. In a 2-screw pump otherwise a 4-screw pump, generally, rotors protrude throughout the pump container into a gear container wherever the timing gears are enclosed. Because of this reason, 4-shaft seals are mandatory within a screw pump through two rotors.

These pumps are named as PC pumps otherwise progressive cavity pumps, and worm Pumps. Generally, these types of pumps are not considered within the family of the screw-pump. Because the rotor in these pumps are not like a usual screw but somewhat a twisted round shaft. A progressive cavity pump includes one shaft with somewhat twisted within the form of a screw, & is enclosed within a pumping hall that is generally rubber lined.

These pumps are also named as the double screw pump, and it is the most general type used high power applications like weighty oil tube transfer. The screws in the pumps are driven from the motor, & timing gears are generally included to turn the next screw.

These pumps are also named as the triple screw pumps, and these are usually used in small applications like lubrication systems. The screws in the pump are determined from the motor to rotate the remaining two screws which are around it without using timing gears.

These pumps are basically two screw pumps, however with two screws for each rotor in opposite directions. These pumps absorb the liquid within the suction port, then divides evenly & is routed to both pumps ends.

The two liquids flow with the help of the pump towards the center & connect jointly again before leaving the release port. Similar to the double screw pump, this pump includes a timing mechanism to make the second rotor run. These pumps are frequently used within Multi-phase applications & oil transport pipelines.

These pumps are mostly similar like a triple screw pump; however with five screws, not three screws. Similar to the 3 screw pump, this pump includes one diving rotor that drives all the remaining screws. This type of pump is frequently used in many applications like tube oil otherwise hydraulic.

So these pumps are the best choice for the people who work with hard liquids which are not movable & require for shifting them quickly like oil, gas and other high thickness liquids.

These pumps are a good choice for 2-phase fluid as well as gas mixtures. But with the exemption of only pumps, these are not suitable for shifting dirt free liquids at stable rates. Additionally, the difficulty of these pumps frequently comes with amplified protection and small gear as contrasted to more easy pumps.

Most of the pump applications are high viscosity fluids like asphalt, otherwise oil, multi-stage liquid, which means there is fluid and steam mixed jointly within the liquid stream.

Thus, this is all about screw pumps uses, sometimes these pumps are selected based on single suction otherwise double suction. The two screw pumps design is single suction where the liquid enters from one side and exits from another side. Similarly, four screw pumps design is double suction which includes the suction stream that divides into both ends and flows through an exit in the middle. Here is a question for you, what are the problems occurred while operating these pumps?

A screw pump is a type of positive displacement pump that uses two or more screws that intermesh to pressurize fluids and move them in a system. The screws take in fluid then push it out from the other side while increasing its pressure.

Two/Double screw pump (twin screw pump) – These pumps operates by using two intermeshing screws as described above. The pump is often equipped with timing gears located outside the pumping chamber that are lubricated with oil in order to ensure the two screws are rotating properly. Due to the design, the screws are not required to be in direct contact with each other which helps extend the life of the pump.

Three screw pump (triple screw pump) – They utilize one driving screw intermeshed with the other two screws to create pressure and move fluid. The screws do come into contact with each other, which often limits the pump to handling only clean liquids.

There is also a three spindle screw pump commonly used in the offshore and marine industries to move high-pressure viscous fluids. Three screws that rotate in opposite directions drive the liquid forward in a closed chamber and along the screws’ spindles. The pumps are also used to transport viscous fluids with lubricating properties and in a variety of applications including boosting, burners, circulating, fuel-injection, lubrication, oil hydraulics, and others.

Due to their ability to provide high flow rates even in viscous liquids, screw pumps are ideal for fuel transfer, elevators, and other similar industrial applications. Single screw pumps, or Archimedean screw pumps, are used for simple water movement such as for sewage inlet pumps, storm water pumping, drainage pumping, and to move industrial waste water.

Screw pumps offer the highest flow rate of positive displacement pumps which makes them a great choice for those who work with hard to move liquids and need to move them as quickly as possible, as in many oil and gas applications moving fuels, oils, and other high viscosity liquids. Screw pumps are also a good choice for two phase liquid and gas mixtures. However – with the exception of single screw pumps – they are not ideal for moving clean liquids at steady paces. In addition, the complexity of screw pumps often comes with increased maintenance and shorter equipment when compared to more simple pumps.

Blackmer S Series Screw Pumps – These amazing new pumps are self-priming double ended positive displacement pumps offered with or without external timing gears and bearings. Available in double and triple screw models, they provide axial balancing of rotating screws and eliminate metal-to-metal contact with advanced timing technologies.

NETZSCH NOTOS Multi Screw Pump – These screw pumps are designed to work with low to high lubricant fluids, low to high viscosity, shear sensitive, and even chemically aggressive media. They operate by use of a drive screw intermeshing with a driven screw that transfers torque from one component to the other. Available as double, triple, and even quadruple screw pumps.

Maag S Series Screw Pump – These double-suction, self-priming screw pumps come with external bearings and a timing gears transmission. The pumps are ideal for the delivery of fluids free of solid substances and/or with little abrasiveness. They also come with non-timing gear transmission and as multi-phase pumps.

Screw Pump White Paper – Enter your contact info here to download our very own white paper on what a screw pump is. We discuss how the name fails to recognize the different product configurations, as well as the advantages, uses, and design considerations.

Archimedes’ Screw – Screw pumps date back to the Archimedes screw, which was invented by the Greek scientist in around 300 BC. The screw was used to move water for irrigation using one screw fit into a cylinder. Today, a few types of systems still use this design, although most use at least two screws.

Engineer’s Edge – See the schematics for several different types of screw pumps here, as well as get an inside opinion on the pro’s and con’s of screw pumps.

Intelligent Pumps for the Digital Oilfield Global Market Research Study – ARC predicts the future of the market in this five year study and includes interesting facts in relation to pumps.

The PZ series of triple screw pump can be utilised for a wide range of applications involving fuel oils and lubricating oils not containing solids, ranging in viscosity from 1.2 to 5000cp. The largest pumps in this series are able to achieve high flow rates up to 324m³/hr and medium pressures up to 16 bar.

As standard this positive displacement pump is supplied with in line suction and discharge ports for installation in areas where there are space limitations or where similar size pumps require replacement. The flanges are available in ANSI or DIN configurations. It can be mounted horizontally or vertically depending on customer requirements.

Our screw pumps have numerous benefits over other positive displacement pumps such as gear pumps. They produce low noise levels, are compact as no gearbox is required, produce low pulsations, are excellent at self-priming and can handle fluids containing trapped air.

This self-priming screw pump range is fitted with a maintenance free ball bearing and can be fitted with a built-in relief valve for protecting the system from overpressure.

The PZ series can be fitted with an Atex motor for installation in non-safe areas. It is marine type approved by ABS, BV and RINA and can be marine witness tested by various classification bodies if required.

The PZ series of triple screw pump is available in various grades of cast iron, due to this fact it can be used for a wide range of applications within the marine and industrial markets. Some of the fuels and oils this range can handle include diesel (DO), Marine diesel oil (MDO), Low sulphur marine gas oil (LSMGO), Heavy fuel oil (HFO), lube oil, bitumen, asphalt and many more. Common applications include fuel cargo, fuel transfer, lube oil transfer, lubricating oil circulation, burner/boiler feed, fuel booster, fuel oil separator and many more involving compatible fuels and oils.

The Santoprene diaphragm resists cracking for a long service life and stands up to water and chemicals such as ammonium hydroxide. These pumps have a rugged aluminum housing for moving large volumes of thick sludges and slurries in demanding environments.

Three principal forms exist; In its simplest form (the Archimedes" screw pump or "water screw"), a single screw rotates in a cylindrical cavity, thereby gravitationally trapping some material on top of a section of the screw as if it was a scoop, and progressively moving the material along the screw"s axle until it is discharged at the top. This ancient construction is still used in many low-tech applications, such as irrigation systems and in agricultural machinery for transporting grain and other solids. The second form works differently; it squeezes a trapped pocket of material against another screw. This form is what is typically referred to in modern times with the term "screw pump". The third form (the progressive cavity pump or eccentric screw pump) squeezes a trapped pocket of material against the cavity walls by spinning the screw eccentrically.

Like all positive-displacement pumps, all various kinds of screw pumps function by trapping a volume of material somehow, and then moving it. There are numerous ways to shape the screw or the cavity to accomplish this function, and the number of screws working together can be many. The term "screw pump" refers generically to all of these types. However, this generalization can be a pitfall as it fails to recognize that the different ‘screw" configurations have different advantages and design considerations for each, which lead to the various kinds being suitable for very different use cases, material types, flow rates, and pressures.

One of the most common configurations of a screw pump is the three-spindle screw pump. Three screws press against each other to form pockets of the pumped liquid in the grooves of the screws. As the screws rotate in opposite directions, the pumped liquid moves along the screws" spindles. There is nothing magical about two, three or any number of screws; pockets are formed regardless. Three rather than two spindles are used because this allows the central screw to experience symmetrical pressure loading from all sides. This ensures that the central screw is not pushed sideways, will not be bent, and thus eliminates the need for radial bearings on the main axle to absorb radial forces. The two side screws can then be made as internally-hidden free-floating rollers, lubricated by the pumped liquid itself, thus eliminating the need for bearings on those axles. This is commonly desired because seals and bearings on machines are common sources of failure.

Three-spindle screw pumps are most often used for transport of viscous fluids with lubricating properties. They are suited for a variety of applications such as fuel-injection, oil burners, boosting, hydraulics, fuel, lubrication, circulating, feed, and to pump high-pressure viscous fluids in offshore and marine installations.

Compared to various other pumps, screw pumps have several advantages. The pumped fluid is moving axially without turbulence which eliminates foaming that would otherwise occur in viscous fluids. They are also able to pump fluids of higher viscosity without losing flow rate. Also, changes in the pressure difference have little impact on screw pumps compared to various other pumps. There is also very little back-drive on the power axle, and the output of the flow is typically very even and doesn"t pulsate much.

The screw pump is the oldest positive displacement pump.Ancient Egypt before the 3rd century BC.Nile, was composed of tubes wound round a cylinder; as the entire unit rotates, water is lifted within the spiral tube to the higher elevation. A later screw pump design from Egypt had a spiral groove cut on the outside of a solid wooden cylinder and then the cylinder was covered by boards or sheets of metal closely covering the surfaces between the grooves.

A cuneiform inscription of Assyrian king Sennacherib (704–681 BC) has been interpreted by Stephanie DalleyStrabo, who describes the Hanging Gardens as watered by screws.

Excentric screw pump ( progressive cavity pump), Make Seepex, Type BCSB 10-6L, Working pressure max 3-4 bar, Min capacity : 100 l/min at 218 rpm, Max capacity : 150 l/min at 327 rpm. Motor 2,2 kW with 3 PTC Thermistors for external frequency converter ( excl. )

Self-priming eccentric screw pump mounted on a running gear incl. 2/3 hose screw connection with locknut MG90/65 nozzle VA and 2/3 hose screw connection with locknut DN65/65 nozzle VA.

Self-priming eccentric screw pump mounted on a running gear incl. 2/3 hose screw connection with locknut MG90/65 nozzle VA and 2/3 hose screw connection with locknut DN65/65 nozzle VA.

Mixed lot Extenterschneckenpumpen , different manufacturers ( Netzsch, Bornemann, Seepex etc ) for the most part functional - but some not) dismantled from the running screaming.

The pump was overhauled and checked on 09/10/2014 by ESC Technical Service GmbH.see below Johnson_Pump_Repair_report_rotary_lobe_TW3_537_deThe pump has been in stock since October 9, 2014

Screw conveyor with electric motor in very good condition. Screw conveyors are used to safely transport a range of bulk materials from station to station, such as sawdust, bark residues, pellets or other wood waste. Screw conveyors also serve as a material flow regulator, for example, to feed material to subsequent sections of the line, such as hammer mills, presses and other equipment.

Screw conveyors are used to transport bulk materials - sawdust and wood chips, bark, pellets and other green waste. Screw conveyors also serve to buffer and meter the material flow, for example when feeding downstream machines such as hammer mills, presses, etc.

Used Zambelli Pump 50 liters per hour ZAMBELLI brand pump with rubber impeller Suitable for decanting of wine and de stemmed Pump body in bronze Flow reverser Garolla hose connector Tracking shot Capacity about 50 Liters per hour

As complexity has grown in processes and new conditions have been added, screw pump technology has attracted increased interest from facility designers, process engineers and operators across the industry.

The need to improve energy efficiency and operating flexibility while driving down operating costs is the main goal. It is time to revisit conventional approaches to pump selection and take a look at the evolution of screw pumps, determine how they could improve economics and safeguard the vitality of critical processes in process plants and transfer systems.

This article focuses on pump types with multiple screws. All screw pumps are part of the positive displacement family and, as such, are designed to displace flow in direct proportion to the rotary speed of the pump. This runs contrary to hydrodynamic pumps, which rely on kinetic energy.

The tight cavities are formed when the profiles of the screws mesh as the pump rotates, thereby transporting fluids from suction to discharge as it builds up pressure to overcome the downstream back pressure from the system. The screws of the pump are the main pumping elements, where the driven screw or power rotor transfer the torque to one or several idler screws mechanically and hydraulically. The smooth opening and closing pump cavities result in a pump flow with low pulsations and airborne noise.

Most screw pumps are designed to eliminate axial hydraulic thrust either by using balance pistons or by having the screws in an opposed flowing arrangement. The absence of thrust bearings helps to simplify the pump design and eliminate potential wear and maintenance areas.

Most multiple-screw pump designs are self-priming and can work with low suction pressure. They are also gas tolerant and able to handle free and entrained gases without vapor locking. Low internal fluid velocity and the gentle meshing of the rotors also contribute to low shear rates, which is especially important for shear-sensitive, non-Newtonian fluids as well as different kinds of emulsions.

The operational flexibility of the multiple-screw pump is manifested by its ability to work over a large viscosity range, from light hydrocarbons to residues and emulsions. The screws are normally case hardened for improved wear resistance, and customized coatings are occasionally used to protect rotor bores, the rotor liner and pump casing.

Today’s family of screw pumps includes designs that were traditionally used in hydrocarbon processing. Applications are now increasingly found in the chemical, petrochemical, food and biofuel industries. Each pump design has its specific set of operational advantages and possibilities. Finding the right type of pump for specific applications is not only important for the process but also a cost optimization opportunity including the total cost of ownership.

One pump design relies on two screws, one drive and one driven idler screw, which are radially supported by bushings and lubricated by the pumped fluid. The bushings are also part of the axial thrust balance configuration where discharge pressure on one side of the journal and suction pressure on the other side creates a pressure balance while providing liquid for lubrication and cooling.

The torque transfer from one screw to the other happens by means of a rolling (as opposed to sliding) contact over the screw profile, providing good wear resistance. These screws are running with radial clearance to the bores, which makes this pump design resistant to abrasive wear and suitable for fluids with low lubricity.

Typical applications of this pump design are with fluids like asphalt, bitumen, pitch, emulsions and oily residues as well as a variety of process fluids like methylenedianiline (MDA) and methylene diphenyl diisocyanate (MDI), biofuels and vegetable oils.

In order to eliminate vapors escaping from the mechanical seal, it can be replaced by a vapor-tight mag drive to eliminate greenhouse gas (GHG) releases. It is often a good alternative to the timed twin-screw pump.

The three-screw pump is used in a number of applications where the fluids range from lube oil in lubrication systems to process fluids like pitch, asphalt and light end products, such as condensate and vacuum gas oil (VGO). The most common pump execution used in process applications has a pumping cartridge (separate from the casing) to allow for different installation options. This design uses one driven screw called the power rotor, which is doing the major pump work and is surrounded by two idler rotors. They merely serve as rotating seals for the power rotor and are handling the radial forces supported by long journals formed by the rotor bores. Similar to the other screw pump designs, the thrust load is hydraulically balanced without the use of thrust plates or bearings. The design also allows for higher speed, which results in high volumetric efficiency, even at higher pressure and low viscosity fluids. Typical three-screw pumps can provide flow rates up to 2,000 gallons per minute (gpm) with a maximum discharge pressure of 2,500 pounds per square inch (psi).

Many pump manufacturers use a cartridge design, which works for customized installations. The outer casing can be designed so it matches the envelope of an existing pump and can be a direct replacement without changing pipe connections or the driver. By taking advantage of the flexibility of a cartridge design, important process improvement is possible as shown in Image 4.

New process conditions are met by having the pump inlet directly bolted to a suction box. The inlet section of the screws is cut open and can act as an auger “pulling” the fluid into the pump.

For light ends, the three-screw pump offers several advantages. The compact and short design, compared to the commonly used horizontal electrical submersible pump (ESP), makes it notably smaller and less heavy for the same differential pressure. The internal hydraulic thrust balancing eliminates the need for the thrust bearing arrangement and its lubrication system, which is required for the ESP. In addition, the pump is gas tolerant and can handle liquids that are gas entrained without vapor locking or losing suction. It also runs smoothly and quietly outside

The most versatile of all types of screw pumps is the timed twin-screw pump. Although some manufacturers offer programs with standardized twin-screw pumps, they are often customized for a particular fluid, installation and service. They are designed for larger flow capacities than most other screw pumps and can also be designed for high-discharge pressure.  They are used with a large number of different fluids, from nonlubricating, low-viscosity fluids to high viscous heavy oils, bitumen and molasses. Typical twin-screw pumps can cover flow rates up to 6,500 gpm with pressures up to 1,500 psi.

Because the screw profiles rotate without axial and radial contact, the pump is independent of the lubricity of the pumped fluid. However, at a lower viscosity the internal clearances increase the internal slip which is a disadvantage for the volumetric efficiency. The opposite happens when the viscosity increases, the slip decreases and the pump becomes more volumetrically efficient. The double suction flow neutralizes the axial hydraulic force, and the rotors are positioned axially in a bearing arrangement where the radial load is the dominant load.

The twin-screw pump design is widely used in oil fields, refineries, tank terminals, pipelines and chemical plants. As the screws rotate contactless, the flexibility is almost endless when it comes to the nature of fluids it can handle. With variable speed control, a wide flow range can be covered, allowing flow and pressure to stay at a preset level along with low inlet pressure and entrained gas. Polymer emulsion transfer in chemical plants, blending and charge applications in refineries are good process examples. Another of these is the flare knockout drum pump.

The variable pump speed controls the liquid level in the drum, and vapor carry under does not vapor lock the pump as it would with a conventional vertical can pump. The low amount of net positive suction head (NPSH) the pump requires eliminates the pit necessary with a centrifugal pump. The precise flow control is an important aspect in pipeline service where variations in flow can be easily managed by variation of pump speed.

As shown with the types of screw pumps presented, there is almost always a good fit for a particular pumping installation. The widening use of screw pumps is a testament to the versatility and appreciation this type of pump encounters in the marketplace. The development never stops, and recently, new designs for sanitary applications have reached the market. The fundamental characteristics of a screw pump lend themselves to new fluid handling challenges, and we will continue to see new designs being presented to satisfy new demanding pumping requirements.

Spindle screw pumps feature a simple construction that offers high reliability, performance and efficiency for liquid cooling systems. Comprised of a single rotor element that is powered, while two others are idle, spindle screw pumps move fluid axially without turbulence, eliminating foaming that would otherwise occur in viscous fluids. The idle rotors are rotated by liquid pressure, essentially generating a fluid bearing, or hydrodynamic film, that provides radial support similar to journal bearings.

Spindle screw pumps move fluids of higher viscosity without losing flow rate, and pressure changes have little impact on spindle screw pumps This is important in a rotating application, such as a CT gantry system used in a CT scanner, as the pump is able to maintain constant flow and pressure while under high stress caused by high g-forces.

One of the most critical components in a liquid cooling system is the pump. Pumps are in constant operation when the unit is turned on and typically have the shortest mean time between failure (MTBF) of all components due to friction wear of bearings, pump blades and seals. If poorly chosen, the pump will fail prematurely and the liquid cooling system will fail and cause the end instrument to stop working. This can be a problem for expensive medical, laser or semiconductor equipment where hundreds of thousands of dollars could be lost per day. Compared to centrifugal pumps, spindle screw pumps provide higher reliability, performance and efficiency for liquid cooling systems.

Many different types of pumps are available for liquid cooling systems, which can make it difficult choosing the appropriate pump. Each configuration has its own advantage and disadvantage when compared to each another. Positive-displacement pumps like gear pumps, rotary pumps, vane pumps or centrifugal pumps are the most common types of pumps available for medical, industrial laser or semiconductor use. They are cost-effective but can have shorter operating lifetimes and tend to be noisier. Typical operating life is about 9,000 hours.

Designing a liquid cooling system requires specifying the pump head and motor, which is typically sold separately for larger flow rates. Pump performance can be impacted by the motor size, as a poor performing pump head will require a stronger motor. As a result, the motor will be larger, heavier, louder and consume more power than necessary. Another problem that arises from this is the additional heat generated by the larger motor will transfer to the pump and coolant. This will drop the cooling capacity and make the liquid cooling system work harder to compensate for the additional heat transfer losses. Most motors run on AC power due the lower cost of eliminating a universal power supply. Single-phase AC motors are well established and are typically cheaper than three phase AC motors, but are also bigger and less efficient.

Internal mechanical components limit the pump’s operating lifetime because of friction wear. Customers have to replace the pump after reaching a defined MTBF, which is typically 12K hours. This will result in higher service and maintenance costs which are often over looked at time of purchase.

To get the best performance in terms of pressure and flow rate, the tolerances of the mechanical components have to be very precise. For example, the gear pump is a high precision machine with extremely tight fits and tolerances. At a minimum, metal to metal contact is a given for moving parts inside the pump. This can create problems of high friction and abrasion. To reduce friction wear particles contained inside the coolant require a low mesh strainer. This will prevent large particle sizes from entering the narrow clearance tolerances and damage the mechanical components inside the pump. Cavitation, the sudden formation of low pressure bubbles, can also reduce lifetime, generate higher noise and lower pressure drop.

Most pump types do not self-prime, i.e. push coolant through pump from initial start without being gravity fed by coolant. Therefore, the pump needs to be located below the tank reservoir. Most pump types also pulsate when pushing coolant through a liquid circuit, which can be unusable for higher end applications. Pulsations will cause disturbances to maintaining peak performance and also increases vibration, which reduces operational life of a high-end system. To get the best performance and efficiency of a pump, tight tolerances of internal moving parts are required. The tighter the tolerance the better the performance, but this also increases noise and motor performance requirements due to the increase in friction. The tighter clearance of the working parts inside a gear pump are what enable it to efficiently pump coolants in high pressure environments. Low viscosity coolants such as water with glycol or other solvents have more of a tendency to “slip” through these tight clearances due to the higher-pressure discharge side of the pump back to the lower-pressure suction side of the pump. The phenomenon of slip causes a reduction in flow rate and pump efficiency.

Slip is a characteristic of positive displacement pumps and is defined as the quantity of fluid that leaks through internal clearances of a pump per unit of time. It is dependent upon the internal clearances, the differential pressure, the characteristics of the fluid handled, and, in some cases, the speed.

Vane pumps or centrifugal pumps have problems with cavitation. Based on mechanical design, cavitation causes higher noise level and reduced flow rates and operation lifetime. To compensate for this, a separate bypass coolant circuit is required, which results in cause higher costs and assembly.

A screw pump is a positive displacement pump that uses one or several screws to move material along the screw(s) axis. In its simplest form, a single screw rotates in a cylindrical cavity, thereby moving liquids and/or solids along the screw"s spindle. The screw pump is an old technique typically used in lower tech applications, such as irrigation systems and in agricultural machinery for transporting grain and other solids.

Spindle screw pumps also have a simple construction. A three-screw pump, for example, features a single rotor element that is powered, while two others are idle. The idle rotors are rotated by liquid pressure, essentially generating a fluid bearing, or hydrodynamic film, that provides radial support similar to journal bearings. Symmetrical pressure loading on the power rotor eliminates the need for radial bearings to absorb radial forces.

The pump head and motor are combined into one waterproof housing unit and can push either oil or water coolant. The fluid delivered by a screw pump does not rotate, but moves linearly. The rotors work like endless pistons, which continuously move forward. Flow through a screw pump is axial and in the direction of the power rotor. The inlet hydraulic coolant that surrounds the spindles is trapped as the spindles rotate. The coolant is pushed uniformly with the rotation of the spindles along the axis and is forced out the other end. Due to this the power consumption is reduced, higher efficiency is achieved and the overall motor size can be reduced. This also enables the spindle screw pump to move fluids of higher viscosity without losing flow rate, and pressure changes have little impact on spindle screw pumps This is important in a rotating application, such as a CT gantry system used in a CT scanner, as the pump is able to maintain constant flow and pressure while under high stress caused by high g-forces.

Long life operation is built into the spindle screw design due to no metal-to-metal contact between moving components. This minimizes friction wear and abrasions that can cause cavitation. The flexible mechanical assembly allows the use of a smaller strainer with higher mesh size that extends maintenance intervals and reduces the overall cost of ownership. No metal-to-metal contact also results in the elimination of pulsations, even at high flow rates, making the unit very quiet during operation. The end result is smooth and quiet operation even at high revolution rates and pressure.

Spindle screw technology is ideally suited for liquid cooling systems in environments that require low noise conditions, such as imaging systems for patient modeling.

Self-priming spindle screw pumps allow an independent flexible positioning within the liquid cooling system. Respective to the cost of ownership the value of highly reliable spindle screw pump is thru high lifetime operation that can span over several years with minimal to no maintenance. This minimizes down time by eliminating the need to turn off the end user system for pump replacement.

Compared to centrifugal pumps, spindle screw pumps offer many advantages including moving fluid axially without turbulence, which eliminates foaming that would otherwise occur in viscous fluids. Spindle screw pumps are also able to pump fluids of higher viscosity without losing flow rate. In addition, pressure changes have little impact on spindle screw pumps, making them ideal for a wide range of applications. Spindle screw pumps provide more consistent, reliable and efficient performance in liquid cooling systems.

A Positive Displacement pump (PD pump) is a mechanical device which displaces a known quantity of liquid for every revolution or cycle that the pump completes. The flow rate through a positive displacement pump is directly proportional to its speed and number of cycles over a given time.

A positive displacement pump works by using a screw, a blade, a vane, a lobe, a gear or diaphragm. It creates a chamber or cavity between the pumping elements and the cavity in which the fluid is temporarily stored is moved by the reciprocating or rotary motion along the pipe to its destination.

Progressive Cavity Pump has a rotor rotating within a housing called a stator. The rotor is always metallic and the stator is made up of a rubber type of material. It looks somewhat like a screw thread – the fluid is between the cavities and the rotary motion of the rotor forces the fluid through from one end to the other. It has a low to moderate capacity, low to high pressure, good solids handling capability, one seal, low shear, constant flow and a low pulsation.

Rotary Lobe Pumphas moderate to high capacity, low to moderate pressure, good solids handling capability, two/four seals, a constant flow and moderate pulsation.

Screw Pump –the screw pump has multi versions known as multi screw pumps featuring moderate to high capacity, high pressures, only lubricative liquids, no solids handling capability, one seal and a constant flow.

Diaphragm Pump – Air Operated Diaphragm Pump has low to moderate capacity, low to moderate pressure, very low efficiencies, no seal and high pulsation.

Positive Displacement pumps are generally used for fluids with a relatively high viscosity. They can be used where high accuracy is required e.g metering or dosing. They can also be used where high pressures are required i.e high pressure washing. Waste Water Treatment is another application e.g Netzsch Tornado Rotary Lobe Pump

The main advantages of a Positive Displacement Pump is that it can handle highly viscous fluids whereas a Centrifugal Pump would be inefficient and require high driver powers. PD pumps also have a good volumetric efficiency & driver power is kept to a minimum. The flow rate is easily adjustable via a speed control because the flow rate is directly proportional to its speed. Driver sizing is not as critical as with a Centrifugal pump because the pump will deliver the known quantity of fluids regardless of system back pressure (losses). A Positive Displacement Pump  can produce a very low shear action in the case of sensitive fluids.

The main disadvantages of a Positive Displacement Pump  vs a Centrifugal pump is that dry running can be catastrophic due to either close clearances of parts or in the case of progressive cavity pumps the interference fit between the rotor and stator. All PD pumps require the installation of a pressure relief valve to prevent failure of the pump or piping in case of accident or closure of the delivery valve or blockage in the piping. Main pd pumps will produce pulsations which can lead to undesirable effects i.e vibration, product damage & water hammer.  PD pumps have a limited flow range ~1000m³/hr vs 180,000m³/hr Centrifugal Pumps. The material of construction of PD pumps are more limited in range of available materials than that of Centrifugal Pumps and finally PD pumps have limited solids handling ability in terms of size and/or content.

A Positive Displacement Pump will usually self-prime due to the very small clearances which exist within the pump. This will help it pull a vacuum and thus expel the air through the pump until the liquid reaches the pump. Care should be taken on the suction line i.e installation of a “goose neck” which will ensure there is some liquid in the pump during the priming cycle which will prevent dry running & consequently failure.

An Air Operated Diaphragm pump (AODD pump) is able to self-prime without any liquid being present but this capability to lift is limited if the line is empty of fluid.

Certain Positive Displacement Pumps can run dry  i.e Air Operated Diaphragm pumps have no parts requiring lubrication or no close clearances between parts. Peristaltic pumps can run dry as the hose is lubricated in a bath of its own fluid. Other types of PD pumps should not be run dry.

Every pump has a NPSH (Net pressure suction head) required to ensure reliable and trouble-free operation without damage caused by cavitation therefore therefore the  system should be designed to ensure there is a sufficient margin between NPSHA (Net pressure suction head available) and NPSHR (Net pressure suction head required).

Unlike a centrifugal pump which produces pressure, a positive displacement pump does not produce pressure – it is the system itself that develops pressure from the pressure drop which then creates a back pressure which largely depends on the flow rate through the system i.e higher flow rates will result in higher losses and as a result a higher back pressure. The back pressure is also dependent on the pressure in the vessel at the point of discharge i.e a hydrogen blanket present or steam. The pressure is controlled largely by the pumping rate, therefore, pressure is controlled by varying the speed of the pump. In cases where the variable speed drive is not deployed the system pressure will be controlled to a degree by the setting of the pressure relief valve.

Positive Displacement Metering pumps are usually used where a high degree of accuracy is required e.g in dosing applications where pH control is required e.g Waste Water Treatment Plants or where filling lines require accuracy of volumes of fluid dispersed into containers.

Flexachem are the leading distributors for Netzsch Positive Displacements Pumps in Ireland – Progressive Cavity Pump, Rotary Lobe Pump (Industrial applications) & Screw Pump. We also supply Inoxpa Sanitary Rotary Lobe Pump and Flotronic Air Operated Diaphragm Pumps for the Food & Beverage & Pharma sectors.

We provide localised technical support & on-site service engineering to support the operational needs of our clients. We also hold a heavily stocked inventory to help take the pressure off you in the event of unexpected emergencies. Why not contact one of our Pump Specialists if you have a particular application in mind.