Author: Dan

Automatic Cylinder Reciprocating System

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Automatic Cylinder Reciprocating System

The hydraulic circuit shown in Fig. 1.8 produces continuous reciprocation of a double-acting cylinder using two sequence valves. Each sequence valve senses the completion of stroke by the corresponding build-up pressure. Each check valve and the corresponding pilot line prevent the shifting of the four-way valve until the particular stroke of the cylinder is completed. […]

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Hydraulic Cylinder Sequencing Circuits

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Hydraulic Cylinder Sequencing Circuits

Hydraulic cylinders can be operated sequentially using a sequence valve. Figure 1.7 shows that two sequence valves are used to sequence the operation of two double-acting cylinders. When the DCV is actuated to its right-envelope mode, the bending cylinder (B) retracts fully and then the clamp cylinder (A) retracts. This sequence of cylinder operation is […]

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Counterbalance Valve Application

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Counterbalance Valve Application

A counterbalance valve (Fig. 1.6) is applied to create a back pressure or cushioning pressure on the underside of a vertically moving piston to prevent the suspended load from free falling because of gravity while it is still being lowered. Valve Operation (Lowering) The pressure setting on the counterbalance valve is set slightly higher than […]

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Control of a Single-Acting Hydraulic Cylinder

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Control of a Single-Acting Hydraulic Cylinder

Figure 1.1 shows that the control of a single-acting,spring return cylinder using a three-way two-position manually actuated, spring offset direction-control valve (DCV). In the spring offset mode, full pump flow goes to the tank through the pressure-relief valve (PRV). The spring in the rod end of the cylinder retracts the piston as the oil from […]

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Bleed-Off Circuit

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Bleed-Off Circuit

Compared to meter-in and meter-out circuits, a bleed-off circuit is less commonly used. Figure 1.10 shows a bleed-off circuit with extend stroke control. In this type of flow control, an additional line is run through a flow-control valve back to the tank. To slow down the actuator, some of the flow is bledoff through the […]

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Meter-Out Circuit

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Meter-Out Circuit

Figure 1.9 shows a meter-out circuit for flow control during the extend stroke. When the cylinder extends, the flow coming from the pump into the cylinder is not controlled directly. However, the flow out of the cylinder is controlled using the flow-control valve (metering orifice). On the other hand, when the cylinder retracts, the flow […]

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Meter-In Circuit

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Meter-In Circuit

Figure 1.8 shows a meter-in circuit with control of extend stroke. The inlet flow into the cylinder is controlled using a flow-control valve. In the return stroke, however, the fluid can bypass the needle valve and flow through the check valve and hence the return speed is not controlled. This implies that the extending speed […]

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Pressure-Compensated Valves

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Pressure-Compensated Valves

Pressure-compensated flow-control valvesovercome the difficulty causedby non-pressure-compensated valves by changing the size of the orifice in relation to the changes in the system pressure. This is accomplished through a spring-loaded compensator spool that reduces the size of the orifice when pressure drop increases. Once the valve is set, the pressure compensator acts to keep the […]

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Non-Pressure-Compensated Valves

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Non-Pressure-Compensated Valves

Non-pressure-compensated flow-control valves are used when the system pressure is relatively constant and motoring speeds are not too critical. The operating principle behind these valves is that the flow through an orifice remains constant if the pressure drop across it remains the same. In other words, the rate of flow through an orifice depends on […]

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Pilot-Operated Unloading Valve

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Pilot-Operated Unloading Valve

A pilot-operated unloading valve has less pressure override than its direct-acting counterpart.So it does not dump part of the flow prematurely. A pilot-operated unloading relief valve is the same as a pilot-operated relief valve with the addition of an unloading spool. Without the unloading spool, this valve would function just like any pilot-operated relief valve. […]

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