A plunger pump is a type of positive displacement pump where the high-pressure seal is stationary and a smooth cylindrical plunger slides though the seal. This makes them different from piston pumps and allows them to be used at high pressures. This type of pump is often used to transfer municipal and industrial sewage.
Piston pumps and plunger pumps are reciprocating pumps that use a plunger or piston to move media through a cylindrical chamber. The plunger or piston is actuated by a steam powered, pneumatic, hydraulic, or electric drive. Piston pumps and plunger pumps are also called well service pumps, high pressure pumps, or high viscosity pumps.
Piston pumps and plunger pumps use a cylindrical mechanism 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. Plunger pumps are used in applications that could range from 70 to 2070 bars. Piston pumps are used in lower pressure applications. The volume of the fluid discharged is equal to the area of the plunger or piston, multiplied by its stroke length. The overall capacity of the piston pumps and plunger pumps can be calculated with the area of the piston or plunger, the stroke length, the number of pistons or plungers and the speed of the drive. The power needed from the drive is proportional to the capacity of the pump.
Seals are an integral part of piston pumps and plunger pumps to separate the power fluid from the media that is being pumped. A stuffing box or packing is used to seal the joint between the vessel where the media is transferred and the plunger or piston. A stuffing box may be composed of bushings, packing or seal rings, and a gland.
Piston pumps and plunger pumps have a number of components that require the choice of materials based upon wear considerations and contact with the media type. Components may have a number of materials used including bronze, brass, steel, stainless steel, iron, nickel alloy, or other material. For example, piston pumps that function in general service or oil service applications may have an iron cylinder and piston with a steel piston rod. The plunger, discharge valves, and suction valves come in contact with the media type transferred; material choices should be considered based on the fluid transferred. In power applications where continuous duty piston pumps and plunger pumps are needed, solid ceramic plungers may be used when in contact with water and oil, but may not be the appropriate choice for use with highly acidic media types.
The difference between piston pumps and plunger pumps as compared to rotary piston pumps is the actual mechanism used to transfer the fluid. The piston elements moving along an axis are called axial piston pumps. Rotary piston pumps typically have an internal rotating mechanism that moves the piston.
Plunger pump heads are preferably used for simple, non-critical fluids. For critical, abrasive, toxic or flammable fluids diaphragm pump heads are recommended.
The reciprocating plunger directly displaces the process fluid. As the plunger and plunger seal are wetted, high operational safety is achieved by optimal selection of plunger material and seal design.
The plunger seal selection is dependent on the fluid, pressure and temperature.
- A History of Mechanical Inventions, Abbott Payson Usher, Courier Dover Publications, 1988, ISBN 048625593X, 9780486255934
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