Yuken Pilot Operated Relief Valves
These valves consist of a balanced piston for bypassing excess flow in hydraulic circuits and a pilot that controls the piston motion and pressure. Placed in a vent circuit, they can perform remote control, unloading, or two-
Specifications of the pilot operated relief valves (Fig. 3.3) are shown in Table 3.1. In addition, low noise and high pressure types (35 MPa (5 076 psi) Max.) are also available.
Figure 3.4 shows characteristics of flow vs. pressure (pressure override) of the relief valve, 3/4-size. Figure 3.5 shows characteristics of flow vs. vent pressure and the minimum adjustment pressure. A vent pressure is a relief pressure released upon opening a vent.
When the flow exceeds a certain level, the vent pressure rapidly increases with flow resistance. The minimum adjustment pressure refers to a relief pressure obtained when the control pressure of the pilot valve is set to the lowest level.
When a relief valve is loaded with a circuit as depicted in Fig. 3.6, the transient pressure characteristics appear as shown in Fig. 3.7. t represents a delay time of the relief valve and T, that of the system. The smaller the pipe capacity and the lower the pipe pressure, the shorter the delays t and T. To evaluate the delays of the entire system, both t and T must be taken into account.
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