What are the classifications of plunger pumps?

When it comes to plunger pumps, there are actually many different types. Plunger pumps are essential components of hydraulic systems. They operate by using the reciprocating motion of plungers within cylinders to change the volume of the sealed chamber, thereby drawing in fluid and increasing its pressure. These pumps offer several advantages, including high rated pressure, a compact design, high efficiency, and convenient flow regulation.

Classification of plunger pumps:

1. Single-plunger pump

The main structure consists of an eccentric wheel, a plunger, a spring, a cylinder, and two check valves. A closed volume is formed between the plunger and the cylinder bore. As the eccentric wheel completes one revolution, the plunger reciprocates once, drawing oil in during the downward stroke and discharging oil during the upward stroke. The volume of oil discharged per revolution of the pump is called the displacement, which depends solely on the pump’s structural parameters.

2. Horizontal Piston Pump

A horizontal plunger pump consists of multiple plungers—typically three or six—arranged in parallel. The crankshaft directly drives the plungers to reciprocate via connecting rods and sliders or an eccentric shaft, thereby drawing in and discharging fluid. These are hydraulic pumps that also employ valve-type flow-distribution mechanisms; they are primarily positive-displacement pumps. In coal-mining hydraulic support systems, emulsion pumps are generally horizontal plunger pumps. Such emulsion pumps supply emulsified fluid to the hydraulic supports at the coal-face working section. Their operating principle is that the rotation of the crankshaft causes the pistons to move back and forth, thus achieving fluid intake and discharge.

3. Shaft Type

An axial piston pump is a type of reciprocating piston pump in which the reciprocating motion of the pistons or plungers is parallel to the central axis of the cylinder. It operates by utilizing the volume changes caused by the reciprocating motion of pistons that are parallel to the drive shaft. Because the pistons and piston bores are cylindrical components that can achieve highly precise mating, the pump exhibits high volumetric efficiency.

4. Straight-Axis Rotating Swashplate

Axial-piston vane pumps are classified as either pressure-fed or self-priming. Most pressure-fed hydraulic pumps employ an air-charged reservoir to supply oil under atmospheric pressure. After each machine start-up, it is essential to wait until the hydraulic reservoir has reached its operating air pressure. If the machine is started with insufficient air pressure in the reservoir, the slide block in the pump will be drawn downward, resulting in abnormal wear of the return plate and pressure plate inside the pump housing.

5. Radial

Radial piston pumps can be classified as valve‑distributed or shaft‑distributed. Valve‑distributed radial piston pumps suffer from high failure rates and low efficiency. In the 1970s and 1980s, shaft‑distributed radial piston pumps were developed to overcome these drawbacks. Due to the inherent structural characteristics of radial pumps, fixed‑shaft radial piston pumps exhibit superior shock resistance, longer service life, and higher control accuracy compared with axial piston pumps. By employing variable pistons and limit pistons to adjust the stator’s eccentricity, it is possible to achieve a very short stroke variation in variable‑stroke pumps. The maximum allowable eccentricity is typically 5–9 mm (depending on displacement), enabling an extremely short variable stroke. The variable‑stroke mechanism is designed for high‑pressure operation and is controlled by a pilot valve, resulting in rapid pump response. Moreover, the radial design eliminates the problem of uneven wear on the sliding pads that plagues axial piston pumps, significantly enhancing shock resistance.

6. Hydraulic

The hydraulic oil tank of a hydraulic piston pump is pressurized by compressed air. The machine can only be operated once the hydraulic oil tank has reached its working pressure upon each startup. There are two types of axial-flow swashplate piston pumps: pressurized and self-priming.