Piston pumps and plunger pumps are reciprocating positive displacement pumps that use a plunger or piston to move media through a cylindrical chamber. They are also called well service pumps, high pressure pumps, or high viscosity pumps because they can deliver high pump pressures and are capable of handling both viscous and solids containing media.

Operation

Piston pumps and plunger pumps are positive displacement pumps, meaning they use contracting and expanding cavities to move fluids. Specifically, they are reciprocating pumps, which have cavities that expand and contract in a reciprocating (back and forth; up and down) motion rather than a circular (rotary) motion. For more information about this category of pumps, visit the Positive Displacement Pumps Selection Guide page on Engineering360.

Single action plunger pump. Image Credit: Animatedsoftware.com

Piston pumps and plunger pumps use a mechanism (typically rotational) to create a reciprocating motion along an axis, which then builds pressure in a cylinder or working barrel to force gas or fluid through the pump. The pressure in the chamber actuates the valves at both the suction and discharge points.

Double-action plunger pump. Image Credit: pistonpump.org

Design

Piston pumps and plunger pumps can be distinguished by design based on type, pump action, and the number of cylinders.

Types

There are many types of piston pumps and plunger pump designs, but they all employ at least one piston moving in an enclosed cylinder. Specific types of designs include axial and radial piston pumps.

Axial piston pumps contain a number of pistons attached to a cylindrical block which move in the same direction as the block's centerline (axially). Much of the pressure and flow control circuitry can be included internally, allowing for reliable operation and simple design of the associated hydraulic system.

Image Credit: Dynex Hydraulics

Here is a video visual of an axial piston pump assembly:

Video Credit: InsaneHydraulics / CC BY-SA 4.0

Radial piston pumps contain pistons arranged like wheel spokes around a cylindrical block. A drive shaft rotates this cylindrical block which pushes or slings the pistons, causing compression and expansion. The eccentricity between the piston housing and cylinder block centerlines determines the piston stroke. These pumps have a low noise level, very high loads at the lowest speeds, and high efficiency.

Image Credit: Hydrowatt

Pump Action

Pump action determines what directions the piston/plunger moves to perform fluid suction and discharge. The diagram illustrates.

Image Credit: Engineers Edge.

• Single acting pumps have one valve on each end, where suction and discharge take place in opposite directions.
• Double acting pumps utilize two valves on each end, allowing suction and discharge in both directions.

Number of Cylinders

The number of pump cylinders is the number of pumping cylinders in the pump. Increasing the number of pump cylinders increases the capacity of the pump.

• Simplex pumps have one cylinder.
• Duplex pumps have two cylinders.
• Multiplex pumps have more than two cylinders.

Specifications

The primary specifications to consider when selecting pumps are flowrate, stroke volume, pump head, pressure, horsepower, power rating, outlet diameter, and operating temperature. These specifications are described in detail in GlobalSpec's Pump Flow page.

Materials

The material(s) of a pump should be considered based on type of application. The base (casing) and housing (cylinder) materials should be of adequate strength and also be able to hold up against the conditions of its operating environment. Materials in contact with the pumped media (the plunger, discharge valves, and suction valves) need to be resistant to any corrosion induced by the fluid. Some materials used are listed below.

Cast iron provides high tensile strength, durability, and abrasion resistance corresponding to high pressure ratings.

Plastics are inexpensive and provide extensive resistance to corrosion and chemical attack.

Steel and stainless steel alloys provide protection against chemical and rust corrosion and have higher tensile strengths than plastics, corresponding to higher pressure ratings.

 Other materials used in pump construction include:

• Aluminum
• Brass and bronze
• Ceramics
• Nickel-alloy

For more information on materials and other pump features, visit GlobalSpec's Pump Features page.

References

Edgeroamer.com - Principles of Hydraulics: Piston Pumps

Engineers Edge - Plunger Pump

Image credits:

Hydraulic Pumps