radial piston pump

RADIAL PISTON PUMP

1. Construction and Operation

The radial piston pump has a number of radial pistons (in similar fashion to the spokes of a wheel) in a cylinder block which revolves around a stationary eccentric cam. In these pumps, the pistons move perpendicularly to the shaft centerline. As the cylinder block rotates, the eccentricity of the cam causes an in-and-out or pumping motion of the pistons. This working principle is illustrated in Fig.4.21.

As could be seen from Fig.4.21, the fluid inflow and outflow at each piston is controlled through revolving ports. During the downstroke, each piston is connected to the fluid inlet and hence the fluid is drawn inside the cylinders. During the upward stroke, each piston is connected to the fluid outlet and hence fluid is discharged outside the pump.

2. Theoretical Flow Rate of a Radial Piston Pump

The theoretical discharge of a radial piston pump can be calculated by using the following relation :

where

e = Eccentricity in m,

Y = Number of pistons,

d = Diameter of piston in m, and

N = Rotor speed in rpm.

3. Advantages and Disadvantages of Piston Pumps

Table 4.8 presents the merits and demerits of employing piston pumps.

Table 4.8. Advantages and disadvantages of piston pumps

Advantages

(i) Piston pumps are capable of delivering high operating pressures.

(ii) They can handle oils in a wide viscosity range.

(iii) They can handle liquids containing vapours and gases.

(iv) They can provide a variable delivery of liquid.

(v) They are self-priming.

(vi) They are quite in operation.

(vii) They have exceptionally long life.

Disadvantages

(i) They tend to be heavy and bulky.

(ii) They have a pulsating discharge.

(iii) Power pumps cannot be operated against a closed discharge. Hence relief valves are required.

(iv) Most types require inlet and discharge valves.

4. Ranges

Piston pumps are available with capacities from 1.25 Lps to 1250 Lps and the discharge pressures from 70 bar to 1400 bar. In addition, these pumps can operate at speeds over 2000 rpm.

Note

Piston pumps can also be classified into simplex, duplex, and triplex pumps. A simplex pump has one drive and one pumping piston; a duplex pump has two of each. Similar, triplex pumps have three fluid handling cylinders. These pumps are built as either single or double acting units. Pumps with more than three cylinders are rarely used in fluid power systems.