Archive for December, 2009

Hydraulic Closed-Center Circuit with Load Sensing

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Hydraulic Closed-Center Circuit with Load Sensing

Load sensing is achieved with a special compensator mounted on a variable displacement pressure-compensated pump. The reader should envision this special compensator mounted on the pump shown in Fig. 4.15. For this analysis, we assume that the special compensator is set to destroke the pump at 200 psi. (The pump develops 200 psi and is …

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Hydraulic Closed-Center Circuit

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Hydraulic Closed-Center Circuit

The closed-center circuit shown in Fig. 4.18 has a variable displacement pump like that shown in Fig. 4.15. The compensator valve spring is a 2500 psi spring. The pump builds 2500 psi before the compensator valve moves to open a pathway for fluid to flow to the yoke actuating piston. The piston extends and forces …

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Open-Center Hydraulic Circuit

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Open-Center Hydraulic  Circuit

The fixed displacement pump shown in Fig. 4.3 delivers 20 GPM continuously. The relief valve is set on 2500 psi. When the DCV is manually shifted, the pump builds pressure to 1300 psi, and the load begins to move. At this point, the operator notices that the load is moving too fast. Remember, the required …

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Hydraulic Load Sensing Efficiency Improvement

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Load sensing was developed to improve the efficiency of a circuit. It requires a variable displacement pump; thus, it is appropriate to discuss it here. An example will illustrate the advantage provided by load sensing. An application requires a maximum flow of 20 GPM at a maximum pressure of 2500 psi. To meet this requirement, …

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Hydraulic Pressure Control Applications

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Hydraulic Pressure Control Applications

1. A backhoe operator controls the speed of the cylinder, which extends the bucket by cracking open the DCV controlling flow of the cylinder. Describe the difference in the “feel” of the controls using the two different relief valves (a) and (b) shown in Fig. 3.31. 2. A 1.79-in3 displacement motor is turning at 804 …

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Hydraulic Brake Valve Application

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Hydraulic Brake Valve Application

A brake valve performs the same function as a counterbalance valve, but it is designed to overcome a key disadvantage. An example will illustrate this point. Suppose a direct-operated counterbalance valve is used in a motor circuit. There are times when the motor load can overrun, and braking is needed for those times. This valve …

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Hydraulic Counterbalance Valve Application

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Hydraulic Counterbalance Valve Application

The counterbalance valve, also called a holding valve, is used to prevent a weight from falling uncontrollably. As an example, consider a press with a two-ton platen (Fig. 3.27). When the directional control is shifted, the platen will fall unless there is a means for creating an opposing hydraulic force. A counterbalance valve accomplishes this …

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Pressure Reducing Valve

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Pressure Reducing Valve

A pressure-reducing valve does not allow pressure downstream of the valve to exceed the set point. Suppose the workpiece must be clamped with two clamps. The second clamp is placed at a point where too much clamping force will damage the workpiece. A pressure-reducing valve is used to limit clamping pressure as shown in Fig. …

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