Page 35 - PNEUMATIC AND HYDRAULIC

These valves are classified according to the function, operation method, and spring

arrangement. The operation method is classified into: manual, mechanical, hydraulic,
solenoid-operated, electro-hydraulic, and pneumatic. Table 2.4 shows classification

of the valves according to the operation method and spring arrangement.

Table 2.4: Classification by Operation Method and Spring Arrangement

2.5 Pressure Control Valve

These are the units ensuring the control of pressure. A throttling orifice is present in
the valve and by variation of orifice, the pressure level can be controlled or at a

particular pressure, a switching action can be influenced. Pressure relief valve,

pressure reducing, sequence, unloading and counterbalance valve are different types
of pressure control valves shown in Figure 2.4.

(a) (b) (c) (d) (e)

Figure 2.4: Pressure Relief Valve Symbol
(a) Relief Valve (b) Sequence Valve (c) Unloading Valve
(d) Counterbalance Valve (e) Reducing Valve

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