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Plunger Pumps

What is a plunger pump?

A type of reciprocating positive displacement pump designed to move fluids and generate high pressures. They have many features in common with other reciprocating pumps such as diaphragm pumps and piston pumps, and they may be used in many of the same applications. They’re primarily known for being high-powered - capable of creating high pressure. However, they also produce pressure pulsations due to the reciprocating plunger.

How do they work?

Plunger pumps consist of three main parts.

  1. First, there’s the power drive. They are typically set in motion by steam, electric, or hydraulic drive mechanisms. Electric motors are the most common type of driver. The drive mechanism converts the normal rotary motion of the motor into a reciprocating motion by means of a crank shaft and connecting rod arrangement, similar to one found in a an automobile engine.
  2. Second, there’s the plunger component, which is composed of a plunger that is connected to the drive mechanism. The plunger moves back and forth inside of a cylinder. The cylinder includes packing rings to keep liquid from leaking past the plunger as it reciprocates.
  3. Third, there is the pumping chamber at the end of the cylinder, which contains an intake check valve and an outlet check valve to prevent the liquid from reversing direction as it passes through the pumping chamber. As the plunger moves away from the pumping chamber, the pumping chamber expands, which creates a vacuum that draws fluid through the intake. And as the plunger moves toward the pumping chamber, the fluid is pushed out of the pumping chamber and on to the system.

There may be more than one plunger and set of check valves within the pump. A plunger pump that has two plungers and two sets of check valves is called a duplex pump. A pump with three plungers and three sets of check valves is called a triplex pump, and one with five is called a quintiplex pump. Triplex and quintiplex version are fairly common.

Plunger pumps tend to produce high pressure pulsations due to the reciprocating motion of the plungers, and the fewer the number of plungers, the higher the pressure pulsations. Many of these systems include a pulsation dampener plumbed into the pump discharge. This is a closed tank with a diaphragm in the middle, with the volume above the diaphragm being filled with air. As the pressure pulses emanate from the pump discharge, the air cavity above the diaphragm in the expansion tank contracts and expands. This absorbs the pulsations, and significantly reduces the pressure pulsations further downstream.

Where are they used?

Because these are capable of generating high levels of pressure, and because many are sturdily built, they’re useful for moving highly viscous or heavy substances such oil. Smaller, lighter duty versions are used as pressure washers. This application usually would utilize a triplex pump.

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