What is the cross-sectional shape of a plunger pump?

        During half of the pump’s rotational cycle, the plunger moves out of the cylinder, increasing the chamber volume; during the other half, the plunger enters the cylinder, decreasing the chamber volume. This reciprocating motion results in the intake and discharge of fluid.

　　The pump displacement can be easily controlled by adjusting the swashplate angle: the larger the angle, the greater the displacement. The swashplate angle can be remotely controlled via a dedicated hydraulic cylinder.

　　The cylinder block and drive shaft of the plunger pump are located in the same plane. The plunger pump is connected to the support plate of the swashplate via a support plate.

　　As the cylinder rotates, the piston pump performs reciprocating motion because the piston shoe follows the inclined surface of the swashplate. This diagram illustrates the suction and discharge operations. The delivery port and the suction port are located in the valve plate, allowing the piston to pass through during both the suction stroke—when it is drawn out—and the discharge stroke—when it is forced back into the delivery port.

　　These types of plunger pumps can also be designed as variable-displacement units. In such designs, a swash plate is mounted on a movable yoke; rotating the yoke about its pivot point changes the angle of the swash plate. The yoke’s position can be adjusted manually, via servo control, or through compressor control. A swash-plate pump features a rotating cylinder that houses the pistons. Spring-loaded pistons are pushed against a fixed swash plate at an angle relative to the cylinder.

　　So, does a plunger pump generate flow?

　　Pressure-compensated control is the fundamental control method for variable-displacement piston pumps. The pump’s swashplate is actuated by a heavy-duty spring and a piston. When the prime mover, motor, or other drive device rotates the pump shaft, the piston pump generates flow.

　　System pressure is directed to one side of the internal piston, which is held in place by a heavy-duty spring. When the force of the system pressure is sufficient to move the piston and overcome the spring force, the swashplate angle changes, reducing the pump flow. The pump then maintains the set pressure, delivering very little or no flow, until the load changes. At that point, the swashplate angle adjusts again, allowing the pump to resume flow.

This is a relatively simple control method, and it’s exactly what you need in certain applications. You simply adjust the spring tension—and that’s it. Keep in mind that you should not adjust the pump’s flow rate until you have built up sufficient system pressure. To achieve full pressure at full flow, you’ll need more horsepower; without additional power, the prime mover will slow down or stall before the pressure begins to compensate and the flow rate starts to decrease.

When you are operating a conveyor belt with a hydraulic motor, and the load is constant, the motor requires approximately 1,500 psi to handle that load. Set the piston pump compensator to 1,600 psi and allow the system to run. In an emergency, your system must also be able to relieve pressure. Use the pump compensator to adjust the system pressure; this should be set several hundred psi higher than the pump compensator. If the two are set too close together, they will compete with each other, causing the pump’s stroke to oscillate and/or the relief valve to cycle on and off, which in turn leads to reduced efficiency, increased heat generation, and vibration.