Archive for January, 2011

Hydraulic Regeneration Circuit

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Hydraulic Regeneration Circuit

A conventional cylinder can exert a larger force extending than retracting because of the area difference between full bore and annulus sides of the piston. The system in Figure 5.41 employs a cylinder with a full bore/annulus ratio of 2:1, and is known as a differential cylinder. Upon cylinder extension, line pressure P is applied …

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Hydraulic Cartridge Logic Valves

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Hydraulic Cartridge Logic Valves

These are simple two position Open/Shut valves using a poppet and seat. Figure 4.46 shows the construction and symbol for a normally open (pilot to close) valve. A normally closed (pilot to open) valve can be constructed as Figure 4.47. Because a cartridge valve is a two position valve, four valves are needed to provide …

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Hydraulic Modular Valves and Manifolds

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Hydraulic Modular Valves and Manifolds

Valves are normally mounted onto a valve skid with piping at the rear, or underneath, to allow quick changes to be made for maintenance purposes. Piping can, however, be dispensed with almost totally by mounting valves onto a manifold block- with interconnections formed by drilled passages in a solid block or by cut-outs on a …

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Hydraulic Time Delay Valves

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Hydraulic Time Delay Valves

Pneumatic time delay valves (Figure 4.28) are used to delay operations where time-based sequences are required. Figure 4.28a shows construction of a typical valve. This is similar in construction to a 3/2 way pilot-operated valve, but the space above the main valve is comparatively large and pilot air is only allowed in via a flow …

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Hydraulic Shuttle Valves

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Hydraulic Shuttle Valves

A shuttle valve, also known as a double check valve, allows pressure in a line to be obtained from alternative sources. It is primarily a pneumatic device and is rarely found in hydraulic circuits. Construction is very simple and consists of a ball inside a cylinder, as shown in Figure 4.25a. If pressure is applied …

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Hydraulic Restriction check valves

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Hydraulic Restriction check valves

The speed of a hydraulic or pneumatic actuator can be controlled by adjusting the rate at which a fluid is admitted to, or allowed out from, a device. A restriction check valve (often called a throttle relief valve in pneumatics) allows full flow in one direction and a reduced flow in the other direction. Figure …

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Hydraulic Pilot-Operated Check Valves

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Hydraulic Pilot-Operated Check Valves

The cylinder in the system in Figure 4.22 should, theoretically, hold position when the control valve is in its centre, off, position. In practice, the cylinder will tend to creep because of leakage in the control valve. Check valves have excellent sealage in the closed position, but a simple check valve cannot be used in …

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Hydraulic Pilot-Operated Valves

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Hydraulic Pilot-Operated Valves

With large capacity pneumatic valves (particularly poppet valves) and most hydraulic valves, the operating force required to move the valve can be large. If the required force is too large for a solenoid or manual operation, a two-stage process called pilot operation is used. The principle is shown in Figure 4.16. Valve 1 is the …

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Hydraulic Rotary valves

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Hydraulic Rotary valves

Rotary valves consist of a rotating spool which aligns with holes in the valve casing to give the required operation. Figure 4.15 shows the construction and symbol of a typical valve with centre off action. Rotary valves are compact, simple and have low operating forces. They are, however, low pressure devices and are consequently mainly …

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Hydraulic Double Acting Piston Cylinders

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Hydraulic Double Acting Piston Cylinders

Most piston-type actuating cylinders are double-acting, which means that fluid under pressure can be applied to either side of the piston to apply force and provide movement. One design of the double-acting cylinder is shown in figure 10-6. This cylinder contains one piston and piston rod assembly. The stroke of the piston and piston rod …

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