Page 37 - PNEUMATIC AND HYDRAULIC

2.6 Flow Control Valve

2.6.1 Restrictor

These valves regulate flow rates in hydraulic circuits. It’s had the advantages of plain

structure, simple operation, and wide range of adjustment. On the other hand, they

cannot accurately control the flow; even through the fixed restriction, the flow varies
with the inlet-outlet differential pressure and the fluid viscosity. Therefore, these

valves are placed where the pressure difference varies little, and high control accuracy
is not required. The one-way restrictors regulate flow in one way, while allowing

reversed flow to freely pass through.

Figure 2.5: Restrictor

2.6.2 Flow Control Valve

These valves consist of a pressure compensator (pressure reducing valve that keeps
the pressure difference constant) and a restrictor. They maintain a constant flow rate,

independent of the inlet-outlet differential pressure. Provided with a sharp-edge

orifice, they can also work regardless of fluid temperature or viscosity. In a circuit
where the flow rate is regulated to a low level, the control flow may be momentarily

exceeded, leading to jumping of the actuator. This phenomenon is related to a time

lag until the pressure compensating piston is properly positioned for flow control. To
prevent the phenomenon, the piston stroke should be adjusted according to the inlet-

outlet differential pressure.

Figure 2.6: Flow Control Valve

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