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Piston Pumps

What is a piston pump?

A type of reciprocating pump designed to move and pressurize fluid using one or more reciprocating pistons, which are normally driven by an electric motor through a crankshaft and connecting rod.

There are many types, but they all employ at least one piston moving in an enclosed cylinder. The piston normally has one or more o-rings on its periphery, to seal against the cylinder as the piston moves. The piston moves back and forth in the cylinder, alternately drawing liquid into the cylinder and then pushing it out under pressure as the volume in the cylinder gets progressively larger and then smaller as the piston reciprocates.

Piston pumps generally work within the following ranges:

  • Flow rate ranges between 5 and 700 gpm
  • Total head (pressure) ranges between 50 and 5,000 psi
  • Horsepower ranges between 1 and 500 hp

How do they work?

Like most types of positive displacement pumps, piston pumps use the force of the pumping mechanism to expand and contract an internal movable volume of liquid. The power to drive the piston is supplied by an electric motor, internal-combustion engine, or other power source - although more primitive piston pumps may be driven by hand, wind, or flowing water. The motion behind the piston is usually rotational.

Check valves on either side of the pumping chamber prevent fluid from flowing in the wrong direction. Piston pumps can have more than one piston and set of check valves. A pump with two pistons and two sets of check valves would be called a duplex pump, one with three would be called a triplex pump, with five a quintiplex, etc.

Piston pumps can be single acting or double acting. The double acting version involves fluid on both sides of the piston, and two sets of check valves, one on each side of the piston. While the piston is in-taking on one side, it is exhausting on the other. Thus, each time the piston moves in one direction from one end to the other, a full pumping cycle (intake and discharge) has been completed. For single acting versions, the piston must move in both directions to complete a full pumping cycle.

Where are they used?

Piston pumps are used as hydraulic pumps to power heavy machinery, and they’re also useful in smaller machines such as paint sprayers. Larger, more robust versions of this pump type are used in oil production and other industrial applications. Axial and radial pumps, both of which consist of several pistons arrayed in a circular cylinder block, are useful in high-tech and advanced industrial applications.

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