Gear Pumps

Because one size does not fit all

What is a Gear Pump?

A Gear Pump, also called a positive displacement pump, or a spin pump, consists of two inter-meshing gears within a metal housing. These gears rotate within the spin pump housing creating pressure that pushes the fluid through the pump, a process commonly referred to as positive displacement. The pumped product fills the space between the gear teeth and the spin pump housing and moves around the gear, much like a waterwheel. The size of the gear teeth and the speed at which they rotate determines the quantity of product metered and pumped. This process allows for highly accurate and measured amounts of fluid to be metered and transferred, commonly known as “positive displacement metering”. Mahr Precision Gear Pumps maintain their high wear resistance and absolute dimensional stability, even under extremes of temperatures, pressures and viscosities.

What is a Positive Displacement Pump?

A positive displacement pump is a type of pump that transfers liquid through the action of gears, screws, vanes, plunger, piston, or diaphragm. There are two main types of positive displacement pumps; Rotary and Reciprocating.

Mahr-Positive-Displacement-Pumps

Rotary Pumps

The rotary pump category includes the most famous types of positive displacement pumps. These pump types use a rotating component to move the liquid. This rotary movement transfers the liquid from the storage tank to the delivery pipe. The most popular types of rotary positive displacement pumps are Gear, Lobe, Screw, Progressive Cavity and Rotary Vane.

Perhaps the most famous type of positive displacement pump, it uses gears to increase fluid pressure. A single stream gear pump has two gears; one is known as driver or power gear, and the other gear is known as driven gear. The driver gear connects with an electric motor by a shaft. The motor supplies power to the shaft and rotates the shaft. As the shaft starts rotating, it supplies rotation to the drive gear, which then rotates the driven gear in the opposite direction. As these gears start their rotation, within the spin pump housing pressure is created that pushes the fluid through the pump. The pumped product fills the space between the gear teeth and the spin pump housing and moves around the gear.

The size of the gear teeth and the speed at which they rotate determines the quantity of product metered and pumped. This process allows for highly accurate and measured amounts of fluid to be metered and transferred, commonly known as “positive displacement metering”. The water wheel is a simple example of gear pump operation.
A lobe pump is similar to a gear pump except the lobes are designed to almost meet, rather than touch and turn each other. The lobes are used to create a suction that draws in fluid and capture in its chamber before passing it through. Lobe pumps are widely used for thick fluids such and pastes. Commonly used in paper and pulp, pharma, biotech, cosmetic, oil, gas and wastewater industries.

Screw pumps work very much like a gear pump, but with screws instead of gears. This pump has a series of screws (driver and driven screws) that mesh with each other. The rotation of the screws plays a large part in the suction and pressurization of the fluid. When the screws start operating, the fluid enters inside the pump via a suction valve. These screws help the fluid to move from the suction side to the discharge side. Common applications for screw pumps include irrigation systems and also agricultural machinery for transporting grain and other solids.

Progressive cavity pumps transfer fluid by means of the progress through the pump. In a sequence of small, fixed shape, discrete cavities, the fluid is transferred as the pump rotor is turned. Mainly used for low to moderately viscous fluids. Can also handle solid filled fluids well. PC pumps serve a wide range of industrial applications such as adhesives, petroleum, food stuff, chemical substances & sludge.

The rotary vane pump operates like a spiral compressor. Rotary pumps have an impeller located eccentrically in a cylindrical casing. The impeller of the vane pump has multiple vanes that rotate according to the rotor rotation. During the rotation, the impeller blades trap the liquid through the housing and the impeller, and release the liquid through the delivery valve. Common applications for these pumps are automatic-transmission pumps, air conditioning, braking, power steering and high-pressure hydraulic pumps.

A well-known type of positive displacement pump, this pump type has a flexible tube, rollers, and rotor. These pumps are used for medical, agricultural, and water treatment applications..

Reciprocating Pumps

A reciprocating pump works by the repeated back & forth movement of either a plunger, piston or diaphragm. These “strokes” or cycles are commonly referred to as reciprocation.

The plunger pump works in the same way as the piston pump. In a plunger pump, the delivered liquid varies according to the plunger size. The seal around the piston or plunger is important to maintain the pumping action and to avoid leaks. In general, a plunger pump seal is easier to maintain than a piston pump since it is stationary at the top of the pump cylinder whereas the seal around a piston is repeatedly moving up and down inside the pump chamber. Sump pumps and well service pumps are common examples of a plunger pump.

The two phases for this pump type are suction and compression. The first cycle or “suction phase” of the piston creates a vacuum, opens an inlet valve, closes the outlet valve and draws fluid into the piston chamber. While the motion of the piston reverses, the inlet valve, now under pressure, is closed and the outlet valve opens allowing the fluid contained in the piston chamber to be discharged, this is the compression phase. The delivered liquid varies according to the cylinder size. Hand pumps and bicycle pumps are common examples of a piston pump.

Diaphragm Pumps are widely applicable in many industries as they can handle a wide range of fluids. The diaphragm pump operates like the plunger pump, but these pumps have a diaphragm for the suction and discharge of the fluid. The membrane (diaphragm) expansion increases the volume of the pump cylinder and draws liquid inside the cylinder. Squeezing the membrane reduces its volume and drains the liquid. Commonly used in applications with abrasive slurry, gels, and shear sensitive food products.

4 MAIN REASONS FOR USING A POSITIVE DISPLACEMENT PUMP:

  • Consistently generates pulseless, accurate and sustained high pressures
  • The ability to pump extremely thick products with viscosities up to 500,000 cP (more in certain cases)
  • Precise control of the volumetric output of the fluid
  • Reduction of product shearing during the pumping process

WHY POSITIVE DISPLACEMENT PUMPS OVER OTHER TYPES OF PUMPS?

There are several advantages of positive displacement pumps over other types of pumps such as piston pumps, progressive cavity (screw pumps), or peristaltic pumps:

  • Positive displacement pumps have tighter pumping tolerances, measured in microns, resulting in greater accuracy in continuous pulseless stream dispensing or shot dosing.
  • Positive displacement pumps have a sustained linear flow during changes in operating speeds, pressures, and temperatures.
  • Positive displacement pumps are constructed of alloy metal allowing for higher operating temperatures; longer pump life, and handling a broader range of abrasive or corrosive raw materials.

ADVANTAGES & DISADVANTAGES OF A POSITIVE DISPLACEMENT GEAR PUMP

Advantages

  • Maintenance is simple

  • It handles an extensive range of viscosities

  • Output is controllable

  • Easy to reconstruct

  • Cavitations are less sensitive

Disadvantages

  • As meshing gears are used, liquid should be free of abrasives

  • The size of gear pumps is limited so it cannot be used for large bulk flow rates.

PUMP TYPE & RATING FOR VARIOUS FLUID CHARACTERISTICS

GearLobeScrewProgressive CavityRotary VanePeristaltic
>100C555242
Abrasives233525
Pressure544232
Chemical555232
Shear242525
Particulates132425
CIP152525
Sanitary151515
Accuracy544424

1 = VERY POOR 2 = POOR 3 = GOOD 4 = VERY GOOD 5 = EXCELLENT

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