Positive-displacement (PD) Pumps

7/29/2019 Positive-displacement (PD) Pumps

1/24

Positive-displacement pump

By definition, positive-displacement (PD) pumps displace a known quantity of liquid with each

revolution of the pumping elements. This is done by trapping liquid between the pumpingelements and a stationary casing. Pumping element designs include gears, lobes, rotary pistons,

vanes, and screws.

PD pumps are found in a wide range of applications -- chemical-processing; liquid delivery;marine; biotechnology; pharmaceutical; as well as food, dairy, and beverage processing. Theirversatility and popularity is due in part to their relatively compact design, high-viscosity

performance, continuous flow regardless of differential pressure, and ability to handle high

differential pressure.

Positive displacement (PD) pumps are divided into two broad classifications, reciprocating and

rotary (Figure 1).

By definition, PD pumps displace a known quantity of liquid with each revolution of the

pumping elements (i.e., gears, rotors, screws, vanes). PD pumps displace liquid by creating a

space between the pumping elements and trapping liquid in the space. The rotation of thepumping elements then reduces the size of the space and moves the liquid out of the pump. PD

pumps can handle fluids of all viscosities up to 1,320,000 cSt / 6,000,000 SSU, capacities up to

1,150 M3/Hr / 5,000 GPM, and pressures up to 700 BAR / 10,000 PSI. Rotary pumps are self-

priming and deliver a constant, smooth flow, regardless of pressure variations.


2/24

Figure 1

The following information is taken from Hydraulic Institute's, Pump Types and Nomenclature,1994. For more detailed information about the rotary pumping principles, see the specific

pumping principles under Pump School'sPumping Principlespage.

Internal Gear. Internal gear pumps (Figure 2) carry fluid betweenthe gear teeth from the inlet to outlet ports. The outer gear (rotor)

drives the inner or idler gear on a stationary pin. The gears create

voids as they come out of mesh and liquid flows into thecavities. As the gears come back into mesh, the volume is reduced

and the liquid is forced out of the discharge port. The crescent

prevents liquid from flowing backwards from the outlet to the inletport.

Figure 2

External Gear. External gear pumps (Figure 3) also use gears

which come in and out of mesh. As the teeth come out of mesh,

liquid flows into the pump and is carried between the teeth and thecasing to the discharge side of the pump. The teeth come back into

mesh and the liquid is forced out the discharge port. External gear

pumps rotate two identical gears against each other. Both gears areFigure 3
http://www.pumpschool.com/principles/index.asphttp://www.pumpschool.com/principles/index.asphttp://www.pumpschool.com/principles/index.asphttp://www.pumpschool.com/principles/index.asp


3/24

on a shaft with bearings on either side of the gears.

Vane. The vanes - blades, buckets, rollers, or slippers - work with a

cam to draw fluid into and force it out of the pump chamber. Thevanes may be in either the rotor or stator. The vane-in rotor pumps

may be made with constant or variable displacement pumping

elements. Figure 4 shows a sliding vane pump. Figure 4

Flexible Member. This principle is similar to the Vane principle

except the vanes flex rather than slide. The fluid pumping andsealing action depends on the elasticity of the flexible

members. The flexible members may be a tube, a vane, or a

liner. Figure 5 shows a flexible vane pump. Figure 5

Lobe. Fluid is carried between the rotor teeth and the pumping

chamber. The rotor surfaces create continuous sealing. Both gearsare driven and are synchronized by timing gears. Rotors include

bi-wing, tri-lobe, and multi-lobe configurations. Figure 6 is a tri-

lobe pump. Figure 6

Circumferential Piston. Fluid is carried from inlet to outlet in

spaces between piston surfaces. Rotors must be timed by separate

means, and each rotor may have one or more piston elements. SeeFigure 7.

Figure 7

Screw. Screw pumps carry fluid in the spaces between the screw

threads. The fluid is displaced axially as the screws mesh.

Single screw pumps (Figure 8) are commonly called progressive

cavity pumps. They have a rotor with external threads and a statorwith internal threads. The rotor threads are eccentric to the axis of

rotation.

Figure 8

Multiple screw pumps have multiple external screw threads. These

pumps may be timed or untimed. Figure 9 shows a three-screw

pump.

Figure 9


4/24

1) Plunger pump: - Plunger pump are reciprocating pump that use a plunger or piston to move

media through a cylindrical chamber. The plunger or piston is actuated by a steam powered,

pneumatic, hydraulic, or electric drive.

Rotary piston and plunger pumps use acrank mechanismto create areciprocating motionalong

an axis, which then builds pressure in a cylinder or working barrel to force gas or fluid throughthe pump. The pressure in the chamber actuates the valves at both the suction and discharge

points. Plunger pumps are used in applications that could range from 70 to 2,070 bar (1,000 to

30,000 psi). Piston pumps are used in lower pressure applications. The volume of the fluiddischarged is equal to the area of the plunger or piston, multiplied by its stroke length. The

overall capacity of the piston pumps and plunger pumps can be calculated with the area of the

piston or plunger, the stroke length, the number of pistons or plungers and the speed of the drive.

The power needed from the drive is proportional to the pressure and capacity of the pump.[1]

Seals are an integral part of piston pumps and plunger pumps to separate the power fluid from

the media that is being pumped. Astuffing boxor packing is used to seal the joint between the

vessel where the media is transferred and the plunger or piston. A stuffing box may be composedof bushings, packing or seal rings, and a gland.

Plunger pumps component materials are chosen for wear and contact with the media type.

Component materials include bronze, brass, steel, stainless steel, iron, nickel alloy, or other

material. For example, plunger pumps that function in general service or oil service applicationsoften have an iron cylinder and plunger. The plunger, discharge valves, and suction valves come

in contact with the media type transferred, and material choices are based on the fluid

transferred. In power applications where continuous duty plunger pumps are needed, solid

ceramic plungers may be used when in contact with water and oil, but may not be compatible foruse with highly acidic media types.
http://en.wikipedia.org/wiki/Steam_enginehttp://en.wikipedia.org/wiki/Steam_enginehttp://en.wikipedia.org/wiki/Crank_%28mechanism%29http://en.wikipedia.org/wiki/Crank_%28mechanism%29http://en.wikipedia.org/wiki/Crank_%28mechanism%29http://en.wikipedia.org/wiki/Reciprocating_motionhttp://en.wikipedia.org/wiki/Reciprocating_motionhttp://en.wikipedia.org/wiki/Reciprocating_motionhttp://en.wikipedia.org/wiki/Plunger_pump#cite_note-Evans-1http://en.wikipedia.org/wiki/Plunger_pump#cite_note-Evans-1http://en.wikipedia.org/wiki/Plunger_pump#cite_note-Evans-1http://en.wikipedia.org/wiki/Stuffing_boxhttp://en.wikipedia.org/wiki/Stuffing_boxhttp://en.wikipedia.org/wiki/Stuffing_boxhttp://en.wikipedia.org/wiki/MIMEhttp://en.wikipedia.org/wiki/MIMEhttp://en.wikipedia.org/wiki/Stainless_steelhttp://en.wikipedia.org/wiki/Stainless_steelhttp://en.wikipedia.org/wiki/Stainless_steelhttp://en.wikipedia.org/wiki/MIMEhttp://en.wikipedia.org/wiki/Stuffing_boxhttp://en.wikipedia.org/wiki/Plunger_pump#cite_note-Evans-1http://en.wikipedia.org/wiki/Reciprocating_motionhttp://en.wikipedia.org/wiki/Crank_%28mechanism%29http://en.wikipedia.org/wiki/Steam_engine


5/24

2) Reciprocating diaphragm pump

The diaphragm pump is a lightweight portable positive displacement pump commonly used to

pump liquids, slurries or sludges. The reciprocating diaphragm pump contains diaphragms whichare driven forwards and backwards by a compressed air supply. The diaphragm forms a barrier

between the fluid and the mechanical workings of the pump.

The reciprocating movement of the diaphragm:

draws liquid into the pump through the suction valve on the suction stroke forces liquid out through the discharge valve at high pressure during the discharge stroke.


6/24

A metering pump moves a precise volume of liquid in a specified time period providing an

accurate flow rate.[1]

Delivery of fluids in precise adjustable flow rates is sometimes called

metering. The term "metering pump" is based on the application or use rather than the exactkind of pump used, although a couple types of pumps are far more suitable than most other types

of pumps.

Although metering pumps can pumpwater, they are often used to pumpchemicals,solutions, or

other liquids. Many metering pumps are rated to be able to pump into a high dischargepressure.

They are typically made to meter at flow rates which are practically constant (when averagedover time) within a wide range of discharge (outlet) pressure. Manufacturers provide each of

their models of metering pumps with a maximum discharge pressure rating against which each

model is guaranteed to be able to pump against. An engineer, designer, or user should ensure that

the pressure and temperature ratings and wetted pump materials are compatible for theapplication and the type of liquid being pumped.

Most metering pumps have a pump head and a motor. The liquid being pumped goes through

the pump head, entering through an inlet line and leaving through an outlet line. The motor iscommonly anelectric motorwhich drives the pump head.

Rotary pump

Rotary pumps are used in a wide range of applications -- liquids, slurries, and pastes. And

because rotary pumps displace a known quantity of liquid with each revolution of the pump

shaft, they are a popular choice for metering applications. They can accommodate thin to highviscosity liquids, high vacuums to high pressures, and minute doses to high capacities.

Rotary pumps are available in a number of different pumping principles, each with its ownunique set of advantages and disadvantages.

The following principles comprise the majority, but not all of the rotary pump market. Pleasecheck back as we continue to add principles to the list.

Internal Gear External Gear Lobe Vane Gerotor

Internal Gear Pump Overview

Internal gear pumps are exceptionally versatile. While they are often used on

thin liquids such as solvents and fuel oil, they excel at efficiently pumping thick
http://en.wikipedia.org/wiki/Flow_ratehttp://en.wikipedia.org/wiki/Metering_pump#cite_note-coleparmer-1http://en.wikipedia.org/wiki/Metering_pump#cite_note-coleparmer-1http://en.wikipedia.org/wiki/Metering_pump#cite_note-coleparmer-1http://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Chemicalhttp://en.wikipedia.org/wiki/Chemicalhttp://en.wikipedia.org/wiki/Chemicalhttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Electric_motorhttp://www.pumpschool.com/principles/internal.asphttp://www.pumpschool.com/principles/internal.asphttp://www.pumpschool.com/principles/external.asphttp://www.pumpschool.com/principles/external.asphttp://www.pumpschool.com/principles/lobe.asphttp://www.pumpschool.com/principles/lobe.asphttp://www.pumpschool.com/principles/vane.asphttp://www.pumpschool.com/principles/vane.asphttp://www.pumpschool.com/principles/gerotor.asphttp://www.pumpschool.com/principles/gerotor.asphttp://www.pumpschool.com/principles/gerotor.asphttp://www.pumpschool.com/principles/vane.asphttp://www.pumpschool.com/principles/lobe.asphttp://www.pumpschool.com/principles/external.asphttp://www.pumpschool.com/principles/internal.asphttp://en.wikipedia.org/wiki/Electric_motorhttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Pressurehttp://en.wikipedia.org/wiki/Solutionhttp://en.wikipedia.org/wiki/Chemicalhttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Metering_pump#cite_note-coleparmer-1http://en.wikipedia.org/wiki/Flow_rate


7/24

liquids such as asphalt, chocolate, and adhesives. The useful viscosity range of an internal gear

pump is from 1cPs to over 1,000,000cP.

In addition to their wide viscosity range, the pump has a wide temperature range as well,

handling liquids up to 750F / 400C. This is due to the single point of end clearance (the

distance between the ends of the rotor gear teeth and the head of the pump). This clearance isadjustable to accommodate high temperature, maximize efficiency for handling high viscosityliquids, and to accommodate for wear.

The internal gear pump is non-pulsing, self-priming, and can run dry for

short periods. They're also bi-rotational, meaning that the same pump can

be used to load and unload vessels. Because internal gear pumps have

only two moving parts, they are reliable, simple to operate, and easy tomaintain.

How Internal Gear Pumps Work

1. Liquid enters the suction port between the

rotor (large exterior gear) and idler (smallinterior gear) teeth. The arrows indicate the

direction of the pump and liquid.

2. Liquid travels through the pump between

the teeth of the "gear-within-a-gear" principle.The crescent shape divides the liquid and acts

as a seal between the suction and discharge ports.

3. The pump head is now nearly flooded, just prior to forcing the liquid out of the discharge

port. Intermeshing gears of the idler and rotor form locked pockets for the liquid which assuresvolume control.

4. Rotor and idler teeth mesh completely to form a seal equidistant from the discharge and

suction ports. This seal forces the liquid out of the discharge port.

Advantages

Only two moving parts Only one stuffing box Non-pulsating discharge Excellent for high-viscosity liquids Constant and even discharge regardless

of pressure conditions

Disadvantages

Usually requires moderate speeds Medium pressure limitations One bearing runs in the product pumped Overhung load on shaft bearing
http://www.pumpschool.com/principles/ig_ani.asphttp://www.pumpschool.com/principles/ig_ani.asphttp://www.pumpschool.com/principles/ig_ani.asphttp://www.pumpschool.com/principles/ig_ani.asp


8/24

Operates well in either direction Can be made to operate with one

direction of flow with either rotation

Low NPSH required Single adjustable end clearance Easy to maintain Flexible design offers application

customization

Applications

Common internal gear pump applications include, but are not limited to:

All varieties of fuel oil and lube oil Resins and Polymers Alcohols and solvents Asphalt, Bitumen, and Tar Polyurethane foam (Isocyanate and polyol) Food products such as corn syrup, chocolate, and peanut butter Paint, inks, and pigments Soaps and surfactants Glycol

Materials Of Construction / Configuration Options

Externals (head, casing, bracket) - Cast iron, ductile iron, steel, stainless steel, Alloy20, and higher alloys.

Internals (rotor, idler) - Cast iron, ductile iron, steel, stainless steel, Alloy 20, andhigher alloys.

Bushing - Carbon graphite, bronze, silicon carbide, tungsten carbide, ceramic, colomony,and other specials materials as needed.

Shaft Seal - Lip seals, component mechanical seals, industry-standard cartridgemechanical seals, gas barrier seals, magnetically-driven pumps.

Packing - Impregnated packing, if seal not required.


9/24

External Gear Pump Overview

External gear pumps are a popular pumping principle and are

often used as lubrication pumps in machine tools, in fluid power

transfer units, and as oil pumps in engines.

External gear pumps can come in single or double (two sets of

gears) pump configurations with spur (shown), helical, and

herringbone gears. Helical and herringbone gears typically offera smoother flow than spur gears, although all gear types are

relatively smooth. Large-capacity external gear pumps typicallyuse helical or herringbone gears. Small external gear pumpsusually operate at 1750 or 3450 rpm and larger models operate at

speeds up to 640 rpm. External gear pumps have close tolerances and shaft support on both sides

of the gears. This allows them to run to pressures beyond 3,000 PSI / 200 BAR, making them

well suited for use in hydraulics. With four bearings in the liquid and tight tolerances, they arenot well suited to handling abrasive or extreme high temperature applications.

Tighter internal clearances provide for a more reliable measure of liquid passing through a pump

and for greater flow control. Because of this, external gear pumps are popular for precise transfer

and metering applications involving polymers, fuels, and chemical additives.

How External Gear Pumps Work

External gear pumps are similar inpumping action to internal gear pumps

in that two gears come into and out of
http://www.pumpschool.com/principles/eg_ani.asphttp://www.pumpschool.com/principles/eg_ani.asphttp://www.pumpschool.com/principles/eg_ani.asphttp://www.pumpschool.com/principles/eg_ani.asphttp://www.pumpschool.com/principles/eg_ani.asphttp://www.pumpschool.com/principles/eg_ani.asp


10/24

mesh to produce flow. However, the external gear pump uses two identical gears rotating

against each other -- one gear is driven by a motor and it in turn drives the other gear. Each gear

is supported by a shaft with bearings on both sides of the gear.

1. As the gears come out of mesh, they create expanding volume on the inlet side of the pump.

Liquid flows into the cavity and is trapped by the gear teeth as they rotate.

2. Liquid travels around the interior of the casing in the pockets between the teeth and the casing

-- it does not pass between the gears.

3. Finally, the meshing of the gears forces liquid through the outlet port under pressure.

Because the gears are supported on both sides, external gear pumps are quiet-running and are

routinely used for high-pressure applications such as hydraulic applications. With no overhung

bearing loads, the rotor shaft can't deflect and cause premature wear.

Advantages

High speed High pressure No overhung bearing loads Relatively quiet operation Design accommodates wide variety

of materials

Disadvantages

Four bushings in liquid area No solids allowed Fixed End Clearances

Applications

Common external gear pump applications include, but are not limited to:

Various fuel oils and lube oils Chemical additive and polymer metering Chemical mixing and blending (double pump) Industrial and mobile hydraulic applications (log splitters, lifts, etc.) Acids and caustic (stainless steel or composite construction) Low volume transfer or application



11/24

As the following list indicates, rotary pumps can be

constructed in a wide variety of materials. By precisely

matching the materials of construction with the liquid, superiorlife cycle performance will result.

External gear pumps in particular can be engineered to handleeven the most aggressive corrosive liquids. While external

gear pumps are commonly found in cast iron, newer materials

are allowing these pumps to handle liquids such as sulfuricacid, sodium hypochlorite, ferric chloride, sodium hydroxide,

and hundreds of other corrosive liquids.

Externals (head, casing, bracket) - Iron, ductile iron, steel, stainless steel, high alloys,composites (PPS, ETFE)

Internals (shafts) - Steel, stainless steel, high alloys, alumina ceramic Internals (gears) - Steel, stainless steel, PTFE, composite (PPS)

Bushing - Carbon, bronze, silicon carbide, needle bearings Shaft Seal - Packing, lip seal, component mechanical seal, magnetically-driven pump

A composite external gear

pump performs well incorrosive liquid applications.


12/24

Lobe Pump Overview

Lobe pumps are used in a variety of industries including, pulpand paper, chemical, food, beverage, pharmaceutical, and

biotechnology. They are popular in these diverse industries

because they offer superb sanitary qualities, high efficiency,reliability, corrosion resistance, and good clean-in-place and

sterilize-in-place (CIP/SIP) characteristics.

These pumps offer a variety of lobe options including single, bi-

wing, tri-lobe (shown), and multi-lobe. Rotary lobe pumps are

non-contacting and have large pumping chambers, allowing themto handle solids such as cherries or olives without damage. They

are also used to handle slurries, pastes, and a wide variety of other liquids. If wetted, they offer

self-priming performance. A gentle pumping action minimizes product degradation. They also

offer reversible flows and can operate dry for long periods of time. Flow is relatively

independent of changes in process pressure, so output is constant and continuous.

Rotary lobe pumps range from industrial designs to sanitarydesigns. The sanitary designs break down further depending on the

service and specific sanitary requirements. These requirements

include 3-A, EHEDG, and USDA. The manufacturer can tell youwhich certifications, if any, their rotary lobe pump meets.

How Lobe Pumps Work

Lobe pumps are similar to

external gear pumps in operation

in that fluid flows around theinterior of the casing. Unlike

external gear pumps, however,

the lobes do not make

contact. Lobe contact isprevented by external timing

gears located in the gearbox. Pump shaft support bearings are located in the gearbox, and since

the bearings are out of the pumped liquid, pressure is limited by bearing location and shaft

deflection.

1. As the lobes come out of mesh, they create expanding volume on the inlet side of thepump. Liquid flows into the cavity and is trapped by the lobes as they rotate.
http://www.pumpschool.com/principles/lobe_ani.asphttp://www.pumpschool.com/principles/lobe_ani.asphttp://www.pumpschool.com/principles/lobe_ani.asphttp://www.pumpschool.com/principles/lobe_ani.asphttp://www.pumpschool.com/principles/lobe_ani.asphttp://www.pumpschool.com/principles/lobe_ani.asphttp://www.pumpschool.com/principles/lobe_ani.asphttp://www.pumpschool.com/principles/lobe_ani.asphttp://www.pumpschool.com/principles/lobe_ani.asphttp://www.pumpschool.com/principles/lobe_ani.asp


13/24

2. Liquid travels around the interior of the casing in the pockets between the lobes and the

casing -- it does not pass between the lobes.

3. Finally, the meshing of the lobes forces liquid through the outlet port under pressure.

Lobe pumps are frequently used in food applications because they handle solids withoutdamaging the product. Particle size pumped can be much larger in lobe pumps than in other PD

types. Since the lobes do not make contact, and clearances are not as close as in other PD

pumps, this design handles low viscosity liquids with diminished performance. Loadingcharacteristics are not as good as other designs, and suction ability is low. High-viscosity liquids

require reduced speeds to achieve satisfactory performance. Reductions of 25% of rated speed

and lower are common with high-viscosity liquids.

Advantages

Pass medium solids No metal-to-metal contact Superior CIP/SIP capabilities Long term dry run (with lubrication

to seals)

Non-pulsating discharge

Disadvantages

Requires timing gears Requires two seals Reduced lift with thin liquids

Applications

Common rotary lobe pump applications include, but are not limited to:

Polymers Paper coatings Soaps and surfactants Paints and dyes Rubber and adhesives Pharmaceuticals Food applications (a sample of these is referenced below)

Food and cosmetic products capable of being pumped by lobe rotor pumps. From Dickenson, T. C. 1995. Pumping Manual, 9th Ed. Elsevier Advanced Technology:

Kidlington, Oxford, U.K.

AlcoholApple pure

Apricots

Coffee liquorCordials

Corn oil

GlycerinGooseberries

Gravy

MousseMussels

Mustard

Sorbitol syrupSoup

Soya sauce


14/24

Baby food

BatterBeans

Beer

Beetroot

Biscuit CreamBlackcurrants

BrineBroth

Butter fat

CaramelCastor Oil

Cat food

Cheese curd

Cheese wheyCherries

Chicken pasteChili con carneChocolateChutney

Cockles

Coconut oilCod oil

Corn syrup

Cottage cheeseCotton seed oil

Cranberry juice

Cream

Cream cheeseCustard

Dog foodDough

Eggs - whole

Egg yolkEssences

Evaporated milk

Fish

FlavoringsFondants

Fruit juiceFruit pulpFruit - wholeFruit yogurt

Gelatin

GherkinsGlucose

Hand cream

HoneyHorseradish

Ice cream

Icings

Iodine ointmentJams

JellyKetchup

Lard

Liquid sugarLotions

Malt

Maple syrup

MargarineMarmalade

MarshmallowMarzipanMascaraMayonnaise

Milk

MincemeatMolasses

Nail polish

Nail varnishOffal

Olive oil

Onions

Palm oilPastes

Peanut butterPectin

Perfumes

PiccalilliPie fillings

Pizza toppings

Plasma

Potato saladPreserves

PuresQuinineRice puddingSalad dressing

Shrimps

SoapSolvents

Spirits

StarchesStews

Strawberries

Sugar

SyrupTapioca

TeaTomato ketchup

Tomato paste

Tomato pureToothpaste

Vaseline

Vegetables

VinegarWater

WinesWortYeastYogurt


Externals (head, casing) - Typically 316 or 316L stainless steel head and casing Externals (gearbox) - Cast iron, stainless steel Internals (rotors, shaft) - Typically 316 or 316L stainless steel, non-galling stainless

steel

Shaft Seal - O-rings, component single or double mechanical seals, industry-standardcartridge mechanical seals


15/24

Vane Pump Overview

While vane pumps can handle moderate viscosity liquids, they excelat handling low viscosity liquids such as LP gas (propane), ammonia,

solvents, alcohol, fuel oils, gasoline, and refrigerants. Vane pumps

have no internal metal-to-metal contact and self-compensate for wear,enabling them to maintain peak performance on these non-lubricating

liquids. Though efficiency drops quickly, they can be used up to 500

cPs / 2,300 SSU.

Vane pumps are available in a number of vane configurations including sliding vane ( left),

flexible vane, swinging vane, rolling vane, and external vane. Vane pumps are noted for theirdry priming, ease of maintenance, and good suction characteristics over the life of the

pump. Moreover, vanes can usually handle fluid temperatures from -

32C / -25F to 260C / 500F and differential pressures to 15BAR / 200 PSI (higher for hydraulic vane pumps).

Each type of vane pump offers unique advantages. For example,

external vane pumps can handle large solids. Flexible vane pumps, onthe other hand, can only handle small solids but create good

vacuum. Sliding vane pumps can run dry for short periods of time and

handle small amounts of vapor.

How Vane Pumps Work

Despite the different configurations, most vane pumps operate under the same general principle

described below.

1. A slotted rotor iseccentrically supported in a

cycloidal cam. The rotor is

located close to the wall of thecam so a crescent-shaped cavity

is formed. The rotor is sealed

into the cam by twosideplates. Vanes or blades fitwithin the slots of the impeller. As the rotor rotates (yellow arrow) and fluid enters the pump,

centrifugal force, hydraulic pressure, and/or pushrods push the vanes to the walls of the

housing. The tight seal among the vanes, rotor, cam, and sideplate is the key to the good suction

characteristics common to the vane pumping principle.
http://www.pumpschool.com/principles/vane_ani.asphttp://www.pumpschool.com/principles/vane_ani.asphttp://www.pumpschool.com/principles/vane_ani.asphttp://www.pumpschool.com/principles/vane_ani.asphttp://www.pumpschool.com/principles/vane_ani.asphttp://www.pumpschool.com/principles/vane_ani.asphttp://www.pumpschool.com/principles/vane_ani.asphttp://www.pumpschool.com/principles/vane_ani.asphttp://www.pumpschool.com/principles/vane_ani.asphttp://www.pumpschool.com/principles/vane_ani.asp


16/24

2. The housing and cam force fluid into the pumping chamber through holes in the cam (small

red arrow on the bottom of the pump). Fluid enters the pockets created by the vanes, rotor, cam,

and sideplate.

3. As the rotor continues around, the vanes sweep the fluid to the opposite side of the crescent

where it is squeezed through discharge holes of the cam as the vane approaches the point of thecrescent (small red arrow on the side of the pump). Fluid then exits the discharge port.

Advantages

Handles thin liquids at relatively higherpressures

Compensates for wear through vaneextension

Sometimes preferred for solvents, LPG Can run dry for short periods Can have one seal or stuffing box Develops good vacuum

Disadvantages

Can have two stuffing boxes Complex housing and many parts Not suitable for high pressures Not suitable for high viscosity Not good with abrasives

Applications

Aerosol and Propellants Aviation Service - Fuel Transfer, Deicing Auto Industry - Fuels, Lubes, Refrigeration Coolants Bulk Transfer of LPG and NH3 LPG Cylinder Filling Alcohols Refrigeration - Freons, Ammonia Solvents Aqueous solutions


Externals (head, casing) - Cast iron, ductile iron, steel, and stainless steel. Vane, Pushrods - Carbon graphite, PEEK. End Plates - Carbon graphite Shaft Seal - Component mechanical seals, industry-standard cartridge mechanical seals,

and magnetically-driven pumps.


17/24

Packing - Available from some vendors, but not usually recommended for thin liquidservice

Gerotor Pump Overview

Gerotor pumps areinternal gear pumpswithout the crescent. The rotor is the

internal (drive) gear shown below in gray, and the idler is the external

(driven) gear, shown below in orange. They are primarily suitable for clean,

low pressure applications such as lubrication systems or hot oil filtrationsystems, but can also be found in low to moderate pressure hydraulic

applications.

How Gerotor Pumps Work

1. Liquid enters the suction port between the rotor(gray gear) and idler (orange gear) teeth.

2. Liquid travels through the pump between theteeth of the "gear-within-a-gear" principle. The

close tolerance between the gears acts as a seal

between the suction and discharge ports.

3. Rotor and idler teeth mesh completely to form a

seal equidistant from the discharge and suction
http://www.pumpschool.com/principles/internal.asphttp://www.pumpschool.com/principles/internal.asphttp://www.pumpschool.com/principles/internal.asphttp://www.pumpschool.com/principles/internal.asp


18/24

ports. This seal forces the liquid out of the discharge port.

Advantages

High Speed Only two moving parts Only one stuffing box Constant and even discharge regardless

of pressure conditions

Operates well in either direction Quiet operation Can be made to operate with one

direction of flow with either rotation

Disadvantages

Medium pressure limitations Fixed clearances No solids allowed One bearing runs in the product pumped Overhung load on shaft bearing

Applications

Common gerotor pump applications include, but are not limited to:

Light fuel oils Lube oil Cooking oils Hydraulic fluid


Externals (head, casing) - Cast iron Internals (rotor, idler) - Steel Bushing - Carbon graphite, bronze, and other materials as needed Shaft Seal - Lip seals, component mechanical seals

Packing - Not commonly used for gerotorpumps


19/24

One of the main advantages of the Peristaltic Pump is cleanliness. It also utilizes another

advantage: Fragile blood cells are not damaged by this pump.

The flexible tube (in this drawing its edges are blue and yellow for clarity) is connected on theinlet side to the patient's artery, and on the outlet side to the patient's vein.

In this example three rollers on rotating arms pinch the tube against an arc and move the fluid

along. There are usually three or four sets of rollers.

Peristaltic pumps have a variety of medical applications. They can be used to add nutrients to

blood, to force blood through filters to clean it, or to move blood through the body and lungs

during open heart surgery.

Selection of a positive displacement (PD) rotary pump is not always an easy choice. There arefour common types of PD pumps available: internal gear, external gear, timed lobe, and vane.

Most PD pumps can be adapted to handle a wide range of applications, but some types are better

suited than others for a given set of circumstances.

The first consideration in any application is pumping conditions. Usually the need for a PD pump

is already determined, such as a requirement for a given amount of flow regardless of differentialpressure, viscosity too high for a centrifugal pump, need for high differential pressure, or other

factors.

Inlet conditions, required flow rate, differential pressure, temperature, particle size in the liquid,

abrasive characteristics, and corrosiveness of the liquid must be determined before a pumpselection is made.

A pump needs proper suction conditions to work well. PD pumps are self-priming, and it is often

assumed that suction conditions are not important. But they are. Each PD pump has a minimum

inlet pressure requirement to fill individual pump cavities. If these cavities are not completelyfilled, total pump flow is diminished. Pump manufacturers supply information on minimum inlet


20/24

conditions required. If high lift or high vacuum inlet conditions exist, special attention must be

paid to the suction side of the pump.

INTERNAL GEAR PUMPS

The crescent internal gear pump has an outer or rotor gear thatis generally used to drive the inner or idler gear (Figure 1). The

idler gear, which is smaller than the rotor gear, rotates on a

stationary pin and operates inside the rotor gear. The gearscreate voids as they come out of mesh and liquid flows into the

pump. As the gears come back into mesh, volumes are reduced

and liquid is forced out the discharge port. Liquid can enter the

expanding cavities through the rotor teeth or recessed areas onthe head, alongside the teeth. The crescent is integral with the

pump head and prevents liquids from flowing to the suction portfrom the discharge port.

The rotor gear is driven by a shaft supported by journal or

antifriction bearings. The idler gear contains a journal bearing rotating on a stationary pin in thepumped liquid. Depending on shaft sealing arrangements, the rotor shaft support bearings mayrun in pumped liquid. This is an important consideration when handling an abrasive liquid and

can wear out a support bearing.

The speed of internal gear pumps is considered relatively slow compared to centrifugal types.

Speeds up to 1,150 rpm are considered common, although some small designs operate up to

3,450 rpm. Because of their ability to operate at low speeds, internal gear pumps are well suitedfor high-viscosity applications and where suction conditions call for a pump with minimal inlet

pressure requirements.

For each revolution of an internal gear pump, the gears have a fairly long time to come out of

mesh allowing the spaces between gear teeth to completely fill and not cavitate. Internal gear

pumps have successfully pumped liquids with viscosities above 1,320,000 cSt / 6,000,000 SSUand very low viscosity liquids, such as liquid propane and ammonia.

Internal gear pumps are made to close tolerances and are damaged when pumping large solids.These pumps can handle small suspended particulate in abrasive applications, but gradually wear

and lose performance. Some performance loss is restored by adjusting the pump end clearance.

End clearance is the closeness of the rotor gear to the head of the pump.

Figure 1.Internal gear pumps

are ideal for high-viscosityliquids, but they are damaged

when pumping large solids.
http://www.pumpschool.com/principles/internal.asphttp://www.pumpschool.com/principles/internal.asphttp://www.pumpschool.com/principles/internal.asp


21/24

EXTERNAL GEAR PUMPS

External gear pumps are similar in pumping action to internalgear pumps in that two gears come into and out of mesh to

produce flow (Figure 2). However, the external gear pump uses

two identical gears rotating against each other. Each gear issupported by a shaft with bearings on both sides of each gear.

Typically, all four bearings operate in the pumped liquid.

Because the gears are supported on both sides, external gear

pumps are used for high pressure applications such as

hydraulics. Usually, small external gear pumps operate at 1,750or 3,450 rpm and larger versions operate at speeds up to 640

rpm.

The design of external gear pumps allows them to be made to

closer tolerances than internal gear pumps. The pump is notvery forgiving of particulate in the pumped liquid. Since there

are clearances at both ends of the gears, there is no endclearance adjustment for wear. When an external gear pump wears, it must be rebuilt or replaced.

External gear pumps handle viscous and watery-type liquids, but speed must be properly set forthick liquids. Gear teeth come out of mesh a short time, and viscous liquids need time to fill the

spaces between gear teeth. As a result, pump speed must be slowed down considerably when

pumping viscous liquids.

The pump does not perform well under critical suction conditions. Volatile liquids tend to

vaporize locally as gear teeth spaces expand rapidly. When the viscosity of pumped liquids rises,torque requirements also rise, and pump shaft strength may not be adequate. Pump

manufacturers supply torque limit information when it is a factor.

LOBE PUMPS

Figure 2.External gear pumps(shown is a double pump) are

typically used for high-

pressure applications such ashydraulics.
http://www.pumpschool.com/principles/external.asphttp://www.pumpschool.com/principles/external.asphttp://www.pumpschool.com/principles/lobe.asphttp://www.pumpschool.com/principles/lobe.asphttp://www.pumpschool.com/principles/lobe.asphttp://www.pumpschool.com/principles/external.asp


22/24

Lobe pumps (Figure 3) are similar to external gear pumps in

operation, except the pumping elements or lobes do not make

contact. Lobe contact is prevented by external timing gears.Pump shaft support bearings are located in the timing gear case.

Since the bearings are out of the pumped liquid, pressure is

limited by bearing location and shaft deflection. There is notmetal-to-metal contact and wear in abrasive applications is minimal. Use of multiple mechanicalseals makes seal construction important.

Lobe pumps are frequently used in food applications, because they handle solids without

damaging the pump. Particle size pumped can be much larger in lobe pumps than in other PD

types. Since the lobes do not make contact, and clearances are not as close as in other PD pumps,

this design handles low viscosity liquids with diminished performance. Loading characteristicsare not as good as other designs, and suction ability is low. High-viscosity liquids require

considerably reduced speeds to achieve satisfactory performance. Reductions of 25% of rated

speed and lower are common with high-viscosity liquids.

Lobe pumps are cleaned by circulating a fluid through them. Cleaning is important when the

product cannot remain in the pumps for sanitary reasons or when products of different colors orproperties are batched.

VANE PUMPS

Sliding vane pumps (Figure 4) operate quite differently from

gear and lobe types. A rotor with radial slots, is positioned off-

center in a housing bore. Vanes that fit closely in rotor slotsslide in and out as the rotor turns. Vane action is aided by

centrifugal force, hydraulic pressure, or pushrods. Pumping

action is caused by the expanding and contracting volumescontained by the rotor, vanes, and housing.

Vanes are the main sealing element between the suction anddischarge ports and are usually made of a nonmetallic

composite material. Rotor bushings run in the pumped liquid or

are isolated by seals.

Vane pumps usually operate at 1,000 rpm, but also run at 1,750

rpm. The pumps work well with low-viscosity liquids that

easily fill the cavities and provide good suction characteristics. Speeds must be reduceddramatically for high-viscosity applications to load the area underneath the vanes. These

applications require stronger-than-normal vane material.

Figure 3.Lobes in lobe pumps

do not make contact, because

they are driven by external

timing gears. This designhandles low-viscosity liquids.

Figure 4. Vane pumps have

better dry priming capability

than other positive

displacement pumps.
http://www.pumpschool.com/principles/vane.asphttp://www.pumpschool.com/principles/vane.asphttp://www.pumpschool.com/principles/vane.asp


23/24

Because there is no metal-to-metal contact, these pumps are frequently used with low-viscosity

nonlubricating liquids such as propane or solvent. This type of pump has better dry priming

capability than other PD pumps. Vane pumps can run dry, but are subject to vane wear.

Vane pump are not well suited to handling abrasive applications. Vane pumps have fixed end

clearances on both sides of the rotor and vanes similar to external gear pumps. Once wearoccurs, this clearance cannot be adjusted, but some manufacturers supply replaceable or

reversible end plates.

Pump Selection Guide

AbrasivesThin

LiquidsViscous Solids Dry Prime

Diff.

Pressure

Internal

GearG G E P A G

External

GearP G G P A E

Lobe G A E E A G

Vane P E A P G A

E = Excellent, G = Good, A = Average, P = Poor

Comparisons Between Rotary

and Centrifugal Pumps

Rotary Centrifugal

Max. Viscosity(cSt / SSU)

1,320,000 /6,000,000

550 / 2,500

Max. Capacity

(M3/Hr / GPM)

750 / 3,300 27,250 / 120,000

Pumping

EfficiencyE A

Energy Costs E A

Self-Priming Yes No

Flow Control E PLife-Cycle Cost G G

Initial Cost A E

E = Excellent, G = Good, A = Average, P = Poor


24/24

High-Viscosity Liquids. Internal gear pumps are often

a good choice.

Sanitary Liquids. Sanitary lobe pumps work well for most food,

beverage, pharmaceutical, and biotechnology applications.

Solids. Pump selection depends on the particular

application. For food-type applications containing solids, begin

searching sanitary lobe pumps. For slurries and other industrial-

type solids, start with internal gear pumps.

Corrosive Liquids. Proper selection of the right materials ofconstruction will have the greatest impact on pump

performance. Composite external gear and stainless steelinternal gear pumps are good starting points. Check out PumpSchool's page onhandling abrasive and corrosive liquids.

Abrasive Liquids. A number of factors can combine to

minimize the effects of abrasion. Begin with internal gearpumps manufactured with hardened steel parts.

Toxic, Hazardous, or Hard-To-Seal Liquids. Preventing leaksis critical for handling these fluids. Magnetically-driven or

mechanically sealed internal or external gear pumps offer a good

starting point.

Extreme Temperature Conditions. Internal gear pumps withjacketing features offer excellent temperature control. Learn

more about handling high-temperature liquidsin Pump School's

"Tough Application" section.
http://www.pumpschool.com/applications/Corrosive_Abrasive.pdfhttp://www.pumpschool.com/applications/Corrosive_Abrasive.pdfhttp://www.pumpschool.com/applications/Corrosive_Abrasive.pdfhttp://www.pumpschool.com/applications/High_Temp.pdfhttp://www.pumpschool.com/applications/High_Temp.pdfhttp://www.pumpschool.com/applications/High_Temp.pdfhttp://www.pumpschool.com/applications/Corrosive_Abrasive.pdf

Documents

Positive-displacement (PD) Pumps