Archive for December, 2010

Mechanical Hydraulic Servo Circuit

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Mechanical Hydraulic Servo Circuit

Figure 10.10 shows a mechanical hydraulic servo system with automotive power steering, the sequential operation of which occurs as follows: • The input or command signal is the turning of the steering wheel. • This results in movement of the valve sleeve, which ports oil to the actuator (steering cylinder). • The piston rod moves …

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Hydraulic Fail-Safe Circuit

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Hydraulic Fail-Safe Circuit

Fail-safe circuits are basically designed to prevent injury to the operator or damage to the equipment. In general they prevent any accidental fall or overloading of the equipment. Figure 10.7 shows a fail-safe circuit in which the cylinder is prevented from falling in the event of a hydraulic line rupture. To lower the cylinder, the …

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Hydraulic Cylinder Sequencing Circuit

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Hydraulic Cylinder Sequencing Circuit

From our earlier discussions, we have seen how a sequence valve can be used to create sequential operations in a hydraulic circuit. The circuit depicted in Figure 10.6 contains a hydraulic system in which two sequence valves are used to control the sequence of operation of two double-acting cylinders. When the DCV is shifted into …

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Counterbalance Valve Application

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Counterbalance Valve Application

Figure 10.5 illustrates the use of a counterbalance or backpressure valve to keep a vertically mounted cylinder in upward position during pump idling. The counterbalance valve is set to open at a pressure slightly above the pressure required to hold the piston up. This permits the cylinder to be forced downward, when pressure is applied …

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Water Cooled Hydraulic Heat Exchanger

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Water Cooled Hydraulic Heat Exchanger

Figure 7.26 is an illustration of a common type of water-cooled heat exchanger used in hydraulic systems. This is typically a shell and tube-type heat exchanger. The cooling water is pumped into the heat exchanger and flows around the tube bank. The hydraulic fluid, which is to be cooled, flows through the tubes. While flowing …

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Air Cooled Hydraulic Heat Exchanger

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Air Cooled Hydraulic Heat Exchanger

Figure 7.25 shows an air-cooled heat exchanger. The hydraulic fluid to be cooled is pumped through the tubes that are finned. As the fluid flows through the tubes, air is blown over them. This takes away the heat from the tubes. A fan driven by an electric motor is incorporated in the heat exchanger to …

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Hydraulic Heat Exchangers

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Heat is generated in a hydraulic system because of the simple reason that no component can operate at 100% efficiency. Significant sources of heat include pumps, pressure relief valves and flow control valves. This can cause a rise in temperature of the hydraulic fluid above the normal operating range. Heat is continuously generated whenever the …

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Hydraulic Accumulator as Leakage Compensator

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Hydraulic Accumulator as Leakage Compensator

In this application (Figure 7.23), the accumulator acts as a compensator, by compensating for losses due to internal or external leakage that might occur during an extended period of time, when the system is pressurized, but not in operation. The pump charges the accumulator and the system, until the maximum pressure setting on the pressure …

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Accumulator Auxiliary Power Source

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Accumulator Auxiliary Power Source

This is one of the most common applications of an accumulator. In this application, the purpose of the accumulator is to store the oil delivered by the pump during the work cycle. The accumulator then releases the stored oil on demand, to complete the cycle, thereby serving as a secondary power source to assist the …

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