Direct-Acting Unloading Valve

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A direct-acting unloading valve consists of a spool held in the closed position by a spring. The spool blocks flow from the inlet to the tank port under normal conditions. When a high-pressure fluid from the pump enters at the external-pilot port, it exerts force against the pilot piston. (The small-diameter pilot piston allows the […]

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Pressure-Reducing Valve

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Pressure-Reducing Valve

The second type of valve is a pressure-reducing valve. This type of valve (which is normally open) is used to maintain reduced pressures in specified locations of hydraulic systems. It is actuated by downstream pressure and tends to close as this pressure reaches the valve setting. Schematic diagram of pressure reducing valve is shown in […]

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Compound Pressure Relief Valve

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Compound Pressure Relief Valve

A pilot-operated pressure-relief valve consists of a small pilot relief valve and main relief valve as shown in Fig. 1.4. It operates in a two-stage process: 1. The pilot relief valve opens when a preset maximum pressure is reached. 2. When the pilot relief valve opens, it makes the main relief valve open. The pilot-operated […]

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Pressure-Relief Valves

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Pressure-relief valves limit the maximum pressure in a hydraulic circuit by providing an alternate path for fluid flow when the pressure reaches a preset level. All fixed-volume pump circuits require a relief valve to protect the system from excess pressure. Fixed-volume pumps must move fluid when they turn. When a pump unloads through an open-center […]

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Tandem Cylinder

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Tandem Cylinder

A tandem cylinder, shown in Fig. 1.7, is used in applications where a large amount of force is required from a small-diameter cylinder. Pressure is applied to both pistons, resulting in increased force because of the larger area. The drawback is that these cylinders must be longer than a standard cylinder to achieve an equal […]

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Double-Acting Cylinder with a Piston Rod on Both Sides

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Double-Acting Cylinder with a Piston Rod on Both Sides

A double-acting cylinder with a piston rod on both sides (Fig.1.5)is a cylinder with a rod extending from both ends. This cylinder can be used in an application where work can be done by both ends of the cylinder, thereby making the cylinder more productive. Double-rod cylinders can withstand higher side loads because they have […]

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Spring-Return Single-Acting Cylinder

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Spring-Return Single-Acting Cylinder

A spring-return single-acting cylinder is shown in Fig.1.3.In push type [Fig. 1.3(a)], the pressure is sent through the pressure port situated at the blank end of the cylinder. When the pressure is released, the spring automatically returns the cylinder to the fully retracted position. The vent port is open to atmosphere so that air can […]

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Gravity-Return Single-Acting Cylinder

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Gravity-Return Single-Acting Cylinder

Figure1.2 shows gravity-return-type single-acting cylinders. In the push type [Fig. 1.2(a)], the cylinder extends to lift a weight against the force of gravity by applying oil pressure at the blank end. The oil is passed through the blank-end port or pressure port. The rod-end port or vent port is open to atmosphere so that air […]

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Single-Acting Cylinders

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Single-Acting Cylinders

A single-acting cylinder is simplest in design and is shown schematically in Fig.1.1. It consists of a piston inside a cylindrical housing called barrel. On one end of the piston there is a rod, which can reciprocate. At the opposite end, there is a port for the entrance and exit of oil. Single-acting cylinders produce […]

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Sequencing Circuits

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Sequencing Circuits

In many applications, it is necessary to perform operations in a definite order. Following is one of several such circuits. The components of the system are as follows. A : Reservoir and Filter ; B : Hydraulic Pump ; C : ; Relief valve : D ; F1, F2, G : Relief valve with integral […]

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