Piston pump

A piston pump (plunger pump) is one of the types of volumetric hydraulic machines in which displacers are one or more pistons ( plungers ) that perform reciprocating motion.

Fig. 1. The structural diagram of the simplest single-acting piston pump

Fig. 2. Differential scheme for switching on the piston pump. During the movement of the piston to the left, part of the fluid is discharged into the stock cavity, the volume of which is less than the volume of the displaced fluid due to the fact that part of the volume of the stock cavity is occupied by the stock

Unlike many other positive displacement pumps, piston pumps are not reversible, that is, they cannot operate as hydraulic motors due to the presence of a valve distribution system.

Piston pumps should not be confused with rotary piston pumps, which include, for example, axial piston and radial piston pumps.

Content

Principle of Operation

The principle of operation is as follows: due to the translational movement of the piston, a vacuum is created in the cavity under it, and liquid from the supply (suction) pipe is sucked into it. When the piston moves backward on the suction pipe, the valve that prevents the liquid from flowing back closes and the valve on the discharge pipe opens, which was closed during suction. There, the liquid that was under the piston is displaced, and the process repeats. The disadvantage of such a pump is that the fluid moves through the pipeline at different speeds (jumps). This point is usually bypassed by the creation of pumps in which several pistons. The main advantage is that it is capable of pumping liquid, being unfilled at the time of start-up (dry absorption), and therefore it is usually used where this advantage should be taken.

Fig. 3. Piston operation principle

One type of piston pump is a diaphragm pump .

Ripple Control

One of the drawbacks of piston pumps, as well as other volumetric pumps, are pulsations of supply and pressure. Ripples can be reduced by placing several pistons in a row and connecting them to one shaft so that their work cycles are phase shifted relative to each other at equal angles. Another way to combat pulsation is to use a differential pump switching circuit (Fig. 2), in which fluid is injected not only during the forward stroke of the piston, but also during the reverse stroke.

Double-acting pumps are also widely used, in which both the piston and rod cavities have (in contrast to the differential switching circuit) their valve distribution system. For such pumps, the ripple coefficient is lower, and the efficiency is higher than for single-acting pumps (Fig. 1).

To combat pulsation, hydraulic accumulators are also used, which store energy at the moment of greatest pressure, and give it away at the time of pressure drop.

Application

Piston pumps have been used since antiquity. Their application for water supply is known from the II century BC. Currently, piston pumps are used in water supply systems, in the food and chemical industries, in everyday life. Diaphragm pumps are used, for example, in fuel supply systems in internal combustion engines.

Literature

Hydraulics, hydraulic machines and hydraulic drives: Textbook for engineering universities / T. M. Bashta , S. S. Rudnev, B. B. Nekrasov et al. - 2nd ed., Rev. - M.: Mechanical Engineering, 1982.
Geyer V.G., Dulin V.S., Zarya A.N. Hydraulics and hydraulic drive: Textbook for universities. - 3rd ed., Revised. and add. - M .: Nedra, 1991.