Monthly Archives for December 2009

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 … Continue reading

26. December 2009 by and
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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 … Continue reading

26. December 2009 by and
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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 … Continue reading

26. December 2009 by and
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Hydraulic Load Sensing Efficiency Improvement

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 … Continue reading

26. December 2009 by and
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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) … Continue reading

25. December 2009 by and
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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 … Continue reading

25. December 2009 by and
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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 … Continue reading

25. December 2009 by and
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Hydraulic Sequence Valve and Pressure-Reducing Valve

The sequence valve and pressure-reducing valve have some similar features. It is instructive to compare their symbols side by side (Fig. 3.20). Both valves are externally drained, meaning that there is a separate line from the valve back to the … Continue reading

25. December 2009 by and
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Hydraulic Counterbalance Valve and Brake Valve

The counterbalance valve and brake valve have similar symbols (Fig. 3.26). The single difference is that the brake valve has a remote pilot line in addition to an upstream pilot line. As with the sequence and pressure-reducing valves, a check … Continue reading

25. December 2009 by and
Categories: Hydraulic Pressure Control | Tags: , | 1 comment

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 … Continue reading

25. December 2009 by and
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