3.1.1 Scope
This Standard applies to industrial/commercial rotary positive displacement pumps. It includes: types and nomenclature; definitions; design and application; and installation, operation, and maintenance. It does not include standards on magnetic drives for sealless pumps nor rotary pumps primarily used for fluid power applications.
In order to provide a comprehensive overview of features and attributes of rotary pumps, Paragraphs 3.1.2 through 3.1.8.2.2 contain descriptive material covering the basic technologies highlighted in Figure 3.1. These include a description of each configuration, typical applications, and general operating ranges for commercially available designs for viscosity, flow, and pressure. Operating ranges stated represent only a single hydraulic parameter and do not indicate that all maximum conditions can be met simultaneously. Suppliers should be contacted for such details.
3.1.2 Sliding vane (rigid)
In this rotary pump technology the vane or vanes are moved by a rotor, thereby drawing fluid into and forcing fluid out from the pumping chamber formed in cooperation with the pump casing. These pumps may be made with vanes in either the rotor or stator and with radial hydraulic forces balanced or unbalanced on the rotor. Figure 3.1.2a (page 15) illustrates a vane-in-rotor constant displacement unbalanced pump. Figure 3.1.2b illustrates a vane-in-stator constant displacement unbalanced pump. Vane-in-rotor pumps also may be made with variable displacement pumping elements.
A common design has a number of vanes that are free to move into and out of slots in the pump rotor, which is inside an eccentrically shaped casing that acts as a cam. In this design, when the driver turns the rotor, centrifugal forces, internal pusher rods, and/or pressurized fluids causes the vanes to move outward in their slots and bear against the inner bore of the pump, forming pumping chambers. As the rotor revolves, fluid flows into the area between the vanes (pumping chambers) when they pass the suction port. The fluid is transported around the pump casing until the discharge port is reached. At that point the fluid is squeezed out into the discharge piping.
In variable capacity designs, displacement of the pump is changed by mechanical movement of the cam ring relative to the rotor. Appropriately configured designs do not need relief valves but simply move the cam to compensate for overpressure until the flow is reduced to zero.
Engineered vane materials make these pumps well-suited for low-viscosity, nonlubricating liquids. Such liquids include solvents, fuel oils, gasoline, refrigerants, and liquefied gas. They handle fluid viscosities ranging from 0.5 cSt to 220,000 cSt (1,000,000 SSU), which are used in a wide range of industries from aviation and automotive to textile. In proper configurations they can be used for fluid temperatures from –29°C (–20°F) to 204°C (400°F) and pressures to 20 bar (290 psi).
At volumes below 3 m3/h (13 gpm) direct four-pole motor drives are possible. In general for larger flows up to 570 m3/h (2500 gpm) design rotating speeds are typically below 600 rpm. Because of their versatility they are available in a wide range of materials, such as stainless steel, nodular iron, cast iron, bronze, and aluminum.
3.1.3 Axial piston pumps
In this pump type fluid is drawn in and forced out by multiple pistons that reciprocate within cylinders. The reciprocating motion is created by a cam plate that is inclined at an angle with the pump centerline and does not rotate.
One end of each piston is held in contact with the cam plate as the cylinder block and piston assembly rotates with the driveshaft. This causes the pistons to reciprocate within the cylinders. The length of the piston stroke is proportional to the angle that the cam plate makes with the pump centerline. Valving is accomplished by rotation of the pistons and cylinders over the inlet and outlet ports.
In fixed displacement axial piston pumps the angle of the cam plate with respect to the pump centerline is fixed. In variable displacement axial piston pumps the angle of the cam plate with respect to the pump centerline can be varied.
Axial piston pumps have relatively low flow rates, 70 m3/h (300 gpm), but are capable of operating at pressures to 250 bar (3600 psi). Typical applications include the spraying of clean fluids or high-pressure pumping of lubricants. This type of pump will typically operate at synchronous motor speeds.
Figure 3.1.3 illustrates a fixed displacement axial piston pump.
3.1.4 Flexible member
3.1.4.1 Flexible vane
Another member of the rotary family is the flexible vane pump (sometimes categorized as a flexible impeller pump). These designs have a typical range up to 25 m3/h (110 gpm) and a maximum pressure capability of 4.1 bar (60 psi). They perform a wide variety of transfer duty applications for low-viscosity fluids up to 22,000 cSt (100,000 SSU). Temperature capabilities typically extend to 90°C (195°F) fluids.
The pump uses an elastomer rotating member with enlarged vane tips that form a pumping chamber in conjunction with a casing when the rotor is placed with the shaft centered in the substantially circular casing that incorporates an eccentric section. Discharge forcing action is accomplished as the vane bends in the eccentric section, effectively squeezing liquid from the discharge chamber. This design is shown in Figure 3.1.4.1.
Because of the variety of applications, stationary components are available in various materials, including stainless steel, bronze, steel, cast iron, and nonmetallics. Flexible members are correspondingly available in a broad range including neoprene, nitrile, EPDM, and Viton®.* Some designs have hygienic certifications, and magnetic drive models are available.
This allows a very broad range of industries to be served, from food, beverage, and pharmaceuticals; to chemical and paints; to recreational marine. Flexible vane pumps are typically direct-coupled to the drivers and operate at synchronous motor speeds.
3.1.4.2 Peristaltic
In this type, the fluid pumping and sealing action depends on the elasticity of the flexible member(s). The flexible member may be a tube or a liner. This type of pump is illustrated in Figure 3.1.4.2. The most common type of flexible member pump is the peristaltic pump that has a flexible tube compressed between one or more moving rollers or shoes and a fixed track. The track is curved and the rollers or shoes rotate about an axis coincident with the center of the radius of curvature of the track. The roller or shoe compresses the tubing and pushes the fluid in front of the roller or shoe towards the discharge end of the tubing. The tubing behind the roller expands to full shape and fills with more fluid. The most common peristaltic pumps have two or three rollers or shoes, which permits closure of the tubing between the suction and discharge ends at all times.
The primary advantage of peristaltic pumps is that the fluid contacts only the tubing. Peristaltic pumps are self-priming, do not require seals and valves, and are reversible. They are used in pharmaceutical, chemical, food, and beverage production, and a number of industrial applications. Small peristaltic pumps are used in various medical applications, and the industrial models can be used for pumping slurries, abrasive fluids, fluids with solids in suspension, and low- to medium-viscosity fluids. Peristaltic pumps are available with flow rates up to 80 m3/h (350 gpm) and differential pressures to 16 bar (230 psi).
The smaller models typically operate at speeds below 200 rpm and the larger models are limited to speeds below 100 rpm.
Because only the tubing contacts the fluid, it is available in a variety of materials to ensure compatibility with the fluid being pumped. The life of the tubing depends on the fluid pumped, differential pressure, pump speed, and tubing material.
3.1.5 Lobe
In this design, fluid is carried between rotor lobe surfaces and the pumping chamber from the inlet to the outlet. The rotor surfaces cooperate to provide continuous sealing. The rotors must be timed by separate means. Each rotor has one or more lobes. Figures 3.1.5a and 3.1.5b illustrate a single- and threelobe pump, respectively.
Lobe pumps are available in a number of configurations and are used in a variety of applications and industries. They can pump a variety of fluids, including most low- to medium-viscosity fluids such as slurries, solids in suspension, and shear-sensitive fluids. If wetted by injecting fluid into the pumping chamber prior to starting, they can self-prime, operate dry for brief periods of time, and handle relatively large solids. They are frequently used to handle food products because of their ability to handle solids without damaging the product and their ability to be readily cleaned.
Lobe pumps are available in flow rates up to 900 m3/h (4000 gpm) and can pump fluids with viscosities of 440,000 cSt (2,000,000 SSU). Specific models can operate at temperatures to 177°C (350°F), differential pressures up to 28 bar (400 psi), and can pump fluids with viscosities of 2,000,000 SSU. With smaller lobe pumps (≥47 m3/h [208 gpm]), speeds of 1000 rpm are possible. As the pump capacity per revolution increases, speeds are reduced.
Larger lobe pumps typically operate at speeds of 600 rpm or less, and operating speeds and flow rates are reduced as the fluid viscosity increases.
3.1.6 Gear
In this type of pump, fluid is carried between gear teeth and displaced when they mesh. The surfaces of the rotors cooperate to provide continuous sealing and either rotor is capable of driving the other.
3.1.6.1 External gear
The external gear pump is a positive displacement pump composed of a casing with two meshing gears with external teeth.
One gear is driven by the shaft coupled to a driver. This gear drives the other gear. The rotation of the gears is such that the liquid comes into the inlet port and flows into and around the outer periphery of the two rotating gears. As the liquid comes around the periphery it is discharged to the outlet port (Figure 3.1.6.1). The flow of the pump is regulated by the size of the cavity (volume) between the teeth and the speed of the gears.
Flow from the outlet is further regulated by the amount of liquid that slips back to the inlet port. The amount of slip depends on the side clearance of the gears to the casing, the peripheral clearance of the gear and bore in the casing, gear-to-gear clearance, developed pressure, and viscosity of the liquid. The lower the viscosity, the greater the slippage. Slippage approaches zero at 5000 SSU. As the viscosity increases, the pump speed is lowered to allow the liquid to fill the space between the rotating teeth. Viscosity range is 2 to 400,000 cSt (40 to 2,000,000 SSU).
Most external gear pumps use spur, helical, or herringbone gears. The helical and herringbone gears will deliver more flow and higher pressure. They are quieter than the spur gears but may require more net inlet pressure than a spur gear.
The most common uses for these pumps are to supply fuel oil for burners, gasoline transfer, kerosene, fuel oil, and diesel oil. They are used for hydraulic devices such as elevators and damper controls. They also pump coolants, paints, bleaches, solvents, syrups, glues, lard, greases, asphalt, petroleum, and lube oils and are used in general industrial applications.
External gear pumps can handle small suspended solids in abrasive applications but will gradually wear and lose performance. Materials of construction are dictated by the application and are available in cast iron, ductile iron, bronze, cast steel, and stainless steel. Because of their broad application scope, numerous optional designs are available.
Rated (normal) performance range is 1 to 180 m3/h (5 to 800 gpm), 3.5 to 21 bar (50 to 300 psi), and 0.37 to 75 kW (0.5 to 100 hp). Small external gear pumps frequently operate at four-pole motor speeds (1800 rpm) and have operated at two-pole speeds (3600 rpm). As the pump capacity per revolution increases, speeds are reduced to less than 500 rpm. Operating speeds and flow rates are reduced as the fluid viscosity increases.
3.1.6.2 Internal gear
The internal gear pump is a rotary flow positive displacement pump design, which is well-suited for a wide range of applications due to its relatively low speed and inlet pressure requirements.
These designs have only two moving parts and hence have proven reliable, simple to operate, and easy to maintain.
They are often a more efficient alternative than a centrifugal pump, especially as viscosity increases. Internal gear pumps have one gear with internally cut gear teeth that mesh with the other gear that has externally cut gear teeth. Pumps of this type are made with (Figure 3.1.6.2a) or without (Figure 3.1.6.2b) a crescent-shaped partition. Either gear is capable of driving the other, and the design can be operated in either direction. Designs are available to provide the same direction of flow regardless of the direction of shaft rotation.
As the gears come out of mesh on the inlet side, liquid is drawn into the pump. The gears have a fairly long time to come out of mesh allowing for favorable filling. The mechanical contacts between the gears form a part of the moving fluid seal between the inlet and outlet ports. The liquid is forced out the discharge port by the meshing of the gears.
Internal gear pumps are commercially available in product families with flows from 1 to 340 m3/h (5 to 1500 gpm) and discharge pressures to 16 bar (230 psi) for applications covering a viscosity range of 2 to 400,000 cSt (40 to 2,000,000 SSU). Internal gear pumps are made to close tolerances and typically contain at least one bushing in the fluid. They can be damaged when pumping large solids. They can handle small suspended solids in abrasive applications but will gradually wear and lose performance. Materials of construction are dictated by the application and include cast iron, ductile iron, bronze, cast steel, and stainless steel.
Small internal gear pumps frequently operate at four-pole motor speeds (1800 rpm) and have operated at two-pole speeds (3600 rpm). As the pump capacity per revolution increases, speeds are reduced. Larger internal gear pumps typically operate below 500 rpm. Operating speeds and flow rates are reduced as the fluid viscosity increases.
Pinion-drive internal gear pumps are a distinctive subclass with unique operating characteristics. They are typically direct-drive arrangements operating at two-, four-, and six-pole speeds for flows below 750 L/min (200 gpm) on clear to very light abrasion, low-viscosity, hydrocarbon-based fluids. They are available in single or multistage module designs capable of pressures to 265 bar (4000 psi).
Internal gear pumps are applied in petrochemical, marine, terminal unloading, asphalt, chemical, and general industrial applications for transfer, lubrication, processing, and low-pressure hydraulics handling a wide range of fuel oils, lube oils, and viscous chemicals (both corrosive and noncorrosive). Because of their broad application scope, numerous optional designs are available, such as close-coupled, abrasion resistant, and API Standard compliance considerations.
Figures 3.1.6.2a and 3.1.6.2b illustrate internal gear pumps with and without the crescent-shaped partition, respectively.
3.1.7 Circumferential piston
The circumferential piston pump is a rotary flow positive displacement pump design, which is well-suited for a wide range of applications due to its relatively low speed and inlet pressure requirements and large cavities. These designs have only two moving parts within the fluid chamber and hence have proven reliable. There is no sealing contact between the piston surfaces, which distinguishes this design from gear and screw pumps. External timing gears synchronize the circumferential pistons. As the circumferential piston rotates on the inlet side, the expanding volume draws the liquid into the pump. The liquid is forced out the discharge port by the collapsing cavity on the discharge side.
Circumferential piston pumps are commercially available in product families with flows to 140 m3/h (600 gpm) and discharge pressures to 31 bar (450 psi) for applications covering a viscosity range of 50 to 1,000,000 cSt (200 to 4,500,000 SSU). Circumferential piston pumps are made to close tolerances.
They can pump almost any product that can be moved and can handle rather large solids and shear-sensitive fluids. They are suitable to run dry for extended periods. Shaft supports often are external from the fluid chamber allowing for higher pressure capabilities. Materials of construction are dictated by the application and include cast iron, ductile iron, cast steel, stainless steel, and many exotic materials.
With smaller circumferential piston pumps speeds of 1800 rpm are possible. Larger circumferential pumps typically operate at speeds of 500 rpm or less. Operating speeds and flow rates are reduced as the fluid viscosity increases.
Circumferential piston pumps are used in petrochemical, paper, marine, wastewater, food processing, tank and terminal unloading, asphalt, chemical, and general industrial applications for transfer and processing handling a wide range of liquids and viscous chemicals (both corrosive and noncorrosive). They are particularly suited for high viscosities, shear-sensitive fluids, and applications that may run dry for a period of time or require higher pressure capability than an internal gear or lobe pump can provide.
Figure 3.1.7 illustrates a circumferential piston pump.
3.1.8 Screw
In this pump type, fluid is carried in spaces formed by the screw(s) and the screw housing and is displaced axially from suction to discharge as they mesh.
3.1.8.1 Single screw (progressing cavity)
Single-screw pumps (commonly called progressing cavity pumps) illustrated in Figure 3.1.8.1, have a rotor with external threads and a stator with internal threads. In the simplest form of progressing cavity pump a singlethreaded inner member (rotor) rotates inside a double-threaded outer member (stator). The geometry of the rotor and stator are such that cavities are created between the rotor and stator. In each revolution of the rotor two cavities are formed that progress from one end of the rotor and stator pair to the other end. The geometry of the rotor and stator also causes the rotor to rotate eccentric to the axis of rotation. In most progressing cavity pumps the stator is made of an elastomeric material and the rotor is made of a rigid material. The elastomeric stator attaches to the rotor with a compressive fit between the rotor and stator. Progressing cavity pumps are also available with rigid stators that fit on the rotor with a clearance. Progressing cavity pumps with rigid stators are suited for pumping nonabrasive, medium- to high-viscosity fluids at pressures to 200 bar (2900 psi). Progressing cavity pumps can pump a wide variety of fluids, from less than 1 SSU viscosity to over 2,000,000 SSU viscosity.
They can handle fluids containing abrasives and solid particles up to 9 cm (3.5 in.) in diameter, and can handle multiphase fluids with up to 99% gas. They are capable of self-priming and can suction lift fluids up to 8.5 m (28 ft). They can be used to pump practically any fluid that is compatible with the materials of construction. Progressing cavity pumps are available with flow rates over 850 m3/h (3750 gpm). Standard industrial models are available with differential pressure capabilities up to 70 bar (1040 psi). Models for special applications, such as downhole pumps or viscous fluid applications, have pressure capabilities up to 200 bar (2900 psi) but are usually limited to less than 25 m3/h (110 gpm) flow rates.
Although some of the smaller progressing cavity pump models operate at speeds up to 1800 rpm, most industrial pump models operate at speeds from 150 to 600 rpm. The low operating speeds and rotor and stator design enable progressing cavity pumps to handle delicate and shear-sensitive fluids without damaging the fluid.
3.1.8.2 Multiple-screw pumps
Multiple-screw pumps have multiple external screw threads. Such pumps may be timed or untimed. Figure 3.1.8.2a illustrates a timed screw pump. Figures 3.1.8.2b and 3.1.8.2c illustrate untimed screw pumps.
3.1.8.2.1 Timed screw pump
Within this family there are a broad range of mechanical configurations, from standard designs to highly customized special units. Unique designs deal with elements as fundamental as screw forms, casing configuration, and timing gear types.
Common among the family, however, are two rotating screws positioned by bearing locations and with synchronizing oillubricated timing gear elements on both rotors.
Illustrated in Figure 3.1.8.2a is a timed screw pump. Fluid enters at the center inlet, splits axially into two end suction sections, and, as the rotating screws intermesh, chambers are formed trapping and conveying fluid axially to the center discharge of the pump.
Products of this design handle a wide range of viscosity from ‹2 to 1,000,000 cSt (33 to 4,500,000 SSU). They also have excellent multiphase capabilities and handle typical contaminants such as found in oil production/pipeline applications.
They can be manufactured in a broad range of materials, including those for corrosive applications, making them suitable for chemical industry services. Because of the axial movement of the fluid through the pump and the compact diameter of the rotors, timed screw pumps typically operate at motor speeds (two-, four-, and six-pole).
Pressure capabilities to 104 bar (1500 psi) are available for fuel injection and crude oil pipeline services. Flow ranges to 2700 m3/h (12,000 gpm) are available for marine cargo handling and transfer pump applications. They pump with a minimum of fluid shear also making them suitable for handling non-Newtonian fluids. Temperature capabilities to 315°C (600°F) qualify them for selected refinery process applications where meeting API Standards is also a requirement. They have extremely low net positive inlet pressure required (NPIPR) capabilities for difficult vapor pressure fluid applications and are frequently found to be the pump technology for difficult service applications.
3.1.8.2.2 Untimed screw pump
The untimed rotary screw pump is an axial-flow, multirotor, positive displacement design used in a wide range of applications in pumping clean to mildly abrasive viscous liquids. It is often a more efficient alternative than centrifugal pumps. The design may use two, three, four, or five screws. The most common configuration is the three-screw pump, which consists of a power rotor (drive screw) and two symmetrically opposed idler rotors (driven screws) that mesh within a close-fitting housing forming a succession of cavities to continuously convey fluid to the pump discharge.
Untimed screw pumps are available with a double-ended flow path as illustrated in Figure 3.1.8.2c or with a single-ended flow path as shown in Figure 3.1.8.2b. Timing is accomplished through rotor geometry. In a properly applied three-screw pump, there is no rotor contact because screws are supported radially in their bores and are hydraulically balanced or free to float on a hydrodynamic film created by the pumped liquid. In other untimed screw pump configurations, the screws may be supported in product-lubricated bushings.
Units are commercially available in product families with flows to 1200 m3/h (5300 gpm) and discharge pressures to 310 bar (4500 psi). Applications cover a wide viscosity range from 2 to 220,000 cSt (33 to 1,000,000 SSU) and temperatures from below zero to 274°C (500°F). Because of the axial movement of the fluid and the compact diameter of the rotors, untimed screw pumps typically operate at motor speeds (two-, four-, and six-pole). Screw pumps operate with a minimum of noise, vibration, and fluid pulsation. Other characteristics important in many applications are their good suction capability and low shear rate. Untimed screw pumps are frequently found in installations where extended uninterrupted service life is required.
Materials of construction are dictated by the application and product family with options available in aluminum, cast iron, ductile iron, carbon steel, alloy steel, bronze, and corrosion-resistant materials. Hardened components may be offered for mildly abrasive applications in which internal wear is a function of the amount and nature of particulate present in the pumped liquid, materials of construction, and operating conditions.
Screw pumps are used in oil field, pipeline, refinery, marine, power generation, chemical, hydraulic systems, and general industrial applications for transfer, lubrication, injection, and hydraulics handling a wide range of fluids, such as fuel oils, lube oils and greases, asphalts, noncorrosive viscous chemicals, and high-pressure coolants.
Because of their broad application scope, numerous standard option packages are available, such as machinery attached, close-coupled designs, magnetically driven, and API compliant versions.
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