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Reciprocal Actuator with Counterbalance Valves

This example shows an actuator built of a double-acting cylinder, directional valve, flow control, block of counterbalance valves, power unit, replenishment arrangement, and a control unit.

The cylinder is loaded with an overriding load, which requires the use of counterbalance valves to prevent the load from creeping when the directional valve is in neutral position. The actuator is equipped with a custom model of a 3-position, 4-way directional valve. The valve connects actuator ports A and B to tank in neutral position, while blocking the pressure port P. Ports A and B are connected to port P if electromagnet A is energized. This causes the cylinder to extend due to the difference in the cylinder effective areas. The piston retracts as electromagnet B is energized.

The diagram of a counterbalance valve is shown next to the structure of the model. The valve allows free flow from port A to port B through the check valve, but blocks the flow in the opposite direction unless pressure is applied to port X. The Variable Orifice block simulates the bypass orifice. Spring accumulator SPR_A and replenishment valve RPV are installed to prevent cavitation in the cylinder chamber A.

The simulated actuator cycle starts with the piston rod at initial position. At 0.65 s electromagnet A is energized, causing the piston to extend until it reaches the end of the stroke. On its way forward, both bypass orifices are open and the cylinder differential connection is used to utilize the difference between piston areas. At 11.7 s electromagnet B is energized and the piston retracts to its initial position. On its way back, only bypass valve B is open and fluid to port B is supplied through the check valve.

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