sequence vavles

SEQUENCE VAVLES

1. What are Sequence Valves

• The sequence valves are used to control the fluid flow to ensure several operations in a particular order of priority in the system.

• The sequence valves are another type of pressure control valves, which are also extensively used in hydraulic systems.

• These valves permit several operations to be completed in a sequential order, i.e., one after another. For example, a pressure sequence valve used in a clamping and drilling circuit will permit the clamping operation to take place first and then the drilling operation is accomplished.

• The sequence valves are set to specific pressure levels so as to ensure the priorities of function.

1. Types of Sequence Valves

Sequence valves are basically relief valves with minor modifications and may be either of the direct-acting or compound type.

2. Pilot-Operated (or Compound) Sequence Valve

The construction and operation of a typical pilot-operated sequence valve is illustrated in Fig.6.19(a).

When the system inlet pressure is within the preset valve pressure, the valve allows the fluid freely through the primary port to operate the first phase. When the system inlet pressure exceeds the preset valve pressure, the valve spool moves up. As the spool lifts, flow is diverted to the secondary port to operate the second phase.

The required sequential pressure can be adjusted with the help of the adjusting screw.

3. Graphic Symbol

Fig.6.19(b) represents the symbolic representation of a sequence valve.