An Hydraulic sequencing valve is essentially a normally closed pressure control valve, that is designed to sequence hydraulic operations within hydraulic power packs dependent upon the applied pressure. This valve is used to ensure the beginning of one operation takes place after the first has reached the designed pressure.
When the pressure at inlet port A reaches the set pressure setting, the hydraulic oil is allowed to pass through to the outlet port B at which time it will be able to carry out additional operations in this part of the hydraulic system.
The main spool of the sequence valve is spring loaded to ensure it remains closed at low pressures. The control stage of the valve is fed from port A through a small control orifice. When the pressure at port A reaches the force applied by the adjuster spring the control spool opens allowing the main spool to open. This action allows flow to pass from port A to port B. Pressure in port B will slowly rise due until it matches that of port A. At which time the main spool is fully open and flow may pass freely. It should be noted that the control orifice will pass a pilot flow of typically 1lpm to the tank port to allow operational movements of the control spool.
A typical example of the use of a hydraulic sequence valve would be a bin lifter. Using the sequence valve placed with port A connected to the full bore side of the main lift cylinder. When the main ram reaches the top of the lift stroke the pressure rises opening the sequence valve, the flow then passes through it to the tip cylinder, thus extending it and tipping the bin. Using a second sequence valve in the reverse direction means a single directional control valve can ensure this lift and tip sequence will always be followed.
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