CANOPY ASSEM. 1P0255 - Caterpillar

Illustration 4 g01064431
The more common type of flow control valve is shown in Illustration 4. This valve combines the action of the orifice and dump valve in one moving part. The pressure compensating operation is the same as the bypass pressure compensated flow control valve.The graphic on the left shows flow through the valve. The flow is at the flow rating or less than the flow rating of the valve.The graphic on the right illustrates the flow beginning to exceed the flow rating of the valve. The pressure differential resulting from the flow across the orifice, has become great enough to begin compressing the spring. As the spring compresses, the valve starts to dump the excess oil, as shown.If the flow to the valve increases, the action of the orifice will cause the spring to compress and more flow will be dumped. The metered flow will remain constant as flow to the valve increases or as the flow to the valve decreases.Restrictor Type Pressure Compensated Flow Control Valve
Illustration 5 g01064436
A restrictor type pressure compensated flow control valve is shown in Illustration 5. The controlled oil flow is set by adjusting the needle valve.The compensator spool and bias spring work like a pressure reducing valve. The supply oil pressure is reduced to the pressure that sends the correct oil flow past the needle valve.When the system is off, the spring moves the compensator spool to the left.At start-up, the compensator spool is open to full oil flow and pressure. When the oil flow becomes greater than the setting of the needle valve, the needle valve restricts oil flow. This causes the oil pressure to increase on gauge 2, as shown. The increase in oil pressure is also sensed on the left side of the compensator spool. When the force of the pressure on the left side of the compensator spool overcomes the force of the spring, the compensator spool moves to the right.Although the supply pressure may continue to increase on gauge 1, orifice 1 reduces the oil pressure at the needle valve to the force of the spring. The controlled oil flow pressure is 0 kPa (0 psi). The pressure differential across the needle valve is 1378 kPa (200 psi) which equals the force of the spring.The needle valve is adjusted in order to allow 7.6 L/min (2 US gpm) through orifice 2 when the pressure differential across the needle valve is 1378 kPa (200 psi).In Illustration 5, there is a relief valve (not shown), similar to Illustration 2, that is set at 4134 kPa (600 psi). Excess supply flow would return to the tank through this relief valve.Controlled Oil Pressure
Illustration 6 g01064437
In Illustration 6 the controlled oil pressure is 1378 kPa (200 psi) as shown on gauge 3. The oil pressure in the valve spring chamber is also 1378 kPa (200 psi). The force of the spring chamber oil pressure is added to the force of the spring. The combined forces move the compensator spool to the left. Orifice 1