Piston Pump

Piston pump, also called plunger pump, is one of the oldest styles of pumps that is still in use.  Its design is very simple.  A piston moves in and out of a cylinder.  The fundamental difference between a plunger pump and a piston pump is in a plunger pump, the piston (or plunger) moves through a stationary packed seal and is pushed into the fluid.  For piston pumps, the piston moving up and down contains the seal.  For both types of pumps, the pistons' movement outward decreases the volume available in the cylinder increases, and fluid enters through the one-way inlet valve.  As the piston moves inward, the volume available in the cylinder decreases, the pressure of the fluid increases.  The fluid then is forced out through the outlet valve.  As the piston moves inward, the volume increases, creating a void which is filled with fluid from the inlet valve.

Unlike a centrifugal pump, a power pump does not develop pressure; it only moves the fluid.  Outlet pressure is determined by the downstream process piping or piping system.  If a valve closes during operation or if flow somehow becomes blocked the flow will be delivered independent of the pressure in the discharge piping system.  Also, unlike a centrifugal pump, a piston or plunger pump will not move on its curve due to pressure.  The line will continue to pressure until the pressures exceed the design limits of the pump or piping and failure will occur.  For this reason, all piston pumps must have discharge pressure relief devices to limit the pressure in the piping system and avoid pump or piping failure.

The pumping rate constantly varies from no flow (at the point at which the piston changes direction) to a maximum when the piston is approximately halfway through its stroke.  The inconsistent flow can be reduced by allowing fluid on both sides of the piston to even out the rate on the pump outlet.  This is known as a double acting piston pump.  A single acting piston pump has fluid on one side of the piston.

• Another way to even out flow, is by adding additional cylinders.  The amount of fluid that is moved through the pump is dependent on many different variables.
• Changing the speed of the pumpChanging the number & size of pistonsChanging the stroke length
• Piston and plunger pumps are expensive, but they are extremely reliable and durable.

Piston Pump Types

Piston pumps come in various types, each designed for specific applications and operating conditions.  The choice of piston pump type depends on factors such as the required flow rate, pressure, efficiency, and the specific demands of the application.  Different designs offer varying advantages and are selected based on the intended use and operating conditions.

• Reciprocating Piston Pump  -  Reciprocating piston pumps use one or more pistons that move back and forth within a cylinder to displace fluid.
• Axial Piston Pump  -  Axial piston pumps have pistons arranged in a circular pattern around a central drive shaft.  The pistons reciprocate parallel to the drive shaft.
• Radial Piston Pump  -  Radial piston pumps have pistons arranged in a radial pattern around a central drive shaft.  The pistons move radially in and out of cylinders.
• Swashplate Piston Pump  -  Swashplate piston pumps use a swashplate mechanism to convert rotary motion into reciprocating motion of the pistons.
• Bent Axis Piston Pump  -  Bent axis piston pumps have pistons that reciprocate along a bent axis in response to the rotation of the drive shaft.
• Radial-Axial Piston Pump  -  Combining elements of radial and axial piston pumps, these pumps have pistons that move both radially and axially within cylinders.
• Inline Piston Pump  -  Inline piston pumps have pistons arranged in a straight line, often with multiple pistons side by side.
• Triplex Piston Pump  -  Triplex piston pumps have three pistons that operate in sequence to provide a continuous flow of fluid.

 Piston Pump Characteristics

Piston pumps are a type of positive displacement pump that uses reciprocating pistons to displace fluid and generate flow.  These pumps exhibit several characteristics that define their performance and suitability for different applications.  Understanding these characteristics is needed when selecting a piston pump for a particular application, as it helps in choosing the right pump based on the system requirements and operating conditions.

Positive Displacement  -  Piston pumps are positive displacement pumps, meaning they deliver a constant volume of fluid for each stroke or revolution.  This characteristic makes them suitable for applications requiring precise flow control.
High Pressure Capability  -  Piston pumps are known for their ability to generate high pressures.  The reciprocating motion of pistons can create significant force, making these pumps suitable for applications where high-pressure fluid delivery is essential.
Variable Displacement  -  Many piston pumps are designed with variable displacement, allowing the operator to adjust the pump's output according to the specific requirements of the system.  This feature provides flexibility in controlling flow rates.
Efficiency  -  Piston pumps can be highly efficient, especially in applications that require constant pressure and flow.  The positive displacement design contributes to efficient energy transfer and utilization.
Precise Flow Control  -  The reciprocating motion of pistons allows for precise control over flow rates.  This characteristic is beneficial in applications where accurate dosing or metering of fluids is required.
Versatility  -  Piston pumps can handle a wide range of fluids, including high viscosity liquids and those with abrasive particles.  This versatility makes them suitable for various industrial applications.
Self-Priming Capability  -  Some piston pump designs are self-priming, meaning they can evacuate air from the suction side and initiate pumping without external priming.  This can be advantageous in situations where the pump needs to start with a dry suction line.
Durability and Long Service Life  -  When properly maintained, piston pumps can be durable and have a long service life.  They are often designed to withstand demanding conditions, contributing to their reliability in industrial settings.
Sensitivity to Contaminants  -  While they are versatile, piston pumps can be sensitive to contaminants in the fluid.  Proper filtration is often necessary to prevent damage to the pump components.
Noise and Vibration  -  Piston pumps can produce noise and vibration during operation, which may be a consideration in applications where a quiet and stable environment is crucial.  Additional components, such as dampeners and isolators, may be used to mitigate these effects.
Maintenance Requirements  -  Depending on the design and application, piston pumps may have specific maintenance requirements, including regular inspection of seals and other components to ensure optimal performance.

Piston Pump Applications

Piston pumps find application in a variety of industries and settings where positive displacement pumps with specific characteristics are required.  These examples highlight the versatility of piston pumps across a wide range of industries, where their positive displacement, high pressure capabilities, and precise control are valued for various applications.

Hydraulic Systems  -  Piston pumps are widely used in hydraulic systems for industrial machinery, construction equipment, and other applications that require precise control over fluid flow and high pressure capabilities.
Oil and Gas Industry  -  Piston pumps are utilized in the oil and gas industry for various processes, including wellhead injection, hydraulic fracturing (fracking), and crude oil transfer.
Agricultural Machinery  -  Tractors, combine harvesters, and other agricultural machinery often incorporate piston pumps for hydraulic systems used in steering, lifting, and other functions.
Pressure Washing  -  High pressure piston pumps are commonly employed in pressure washing equipment for tasks such as cleaning buildings, vehicles, and industrial equipment.
Water Jet Cutting  -  Piston pumps are used in water jet cutting machines to generate high pressure water streams for precision cutting of materials like metal, stone, and composites.
Injection Molding  -  Piston pumps are used in injection molding machines to provide precise control over the injection of molten plastic into molds.
Automotive Industry  -  Piston pumps are used in automotive applications, including power steering systems, automatic transmission systems, and hydraulic suspension systems.
Mining Operations  -  Piston pumps play a role in various mining processes, such as transporting slurry, providing hydraulic power for equipment, and assisting in dewatering operations.
Chemical Processing  -  Piston pumps are employed in the chemical industry for metering and transferring chemicals in precise quantities.  Their ability to handle a variety of fluids makes them suitable for diverse chemical processes.
Aviation and Aerospace  -  Aircraft and aerospace applications often use piston pumps for hydraulic systems that control landing gear, flight control surfaces, and other critical components.
Marine Industry  -  In marine applications, piston pumps are used for various purposes, including hydraulic steering systems, anchor handling, and cargo handling.
Food and Beverage Processing  -  Piston pumps are employed in food and beverage processing for tasks such as metering ingredients, pumping sauces, and handling viscous liquids.
Power Generation  -  Piston pumps can be found in power generation systems for hydraulic control of turbines, generators, and other components.
Railway Systems  -  Piston pumps are used in railway applications for hydraulic systems that control braking systems, suspension systems, and other functions.
Medical Equipment  -  Certain medical devices, such as infusion pumps and laboratory equipment, may use piston pumps for accurate and controlled fluid delivery.