By Josh Cosford
A sequence valve is a pressure valve designed to open when its set pressure is reached, providing a path of flow alternate and sequential to the primary circuit. In some ways, a sequence valve is a directional valve, allowing flow to occur. However, it’s just a relief valve with some added features.
The sequence valve was (is?) used for automated hydraulic functions, especially those which occurred naturally from lowest to highest pressure. A clamp and punch operation is typical of the sequence valve automated applications available. A set of clamp cylinders extends to hold the workpiece, and then as the cylinders bottom out, circuit pressure rises. When pressure rises above the sequence valve setting, the valve then opens, providing flow to the punch cylinder. After the material is punched, the cylinders can all be retracted and reset for the next operation.
Although my above example wasn’t true automation, it could be easily achieved with more sequence and cam operated valves. The sequence valve, as I said earlier, is just a relief valve with added features. Typically, a sequence valve is used to operate multiple actuators with just one directional valve, so a bypass check valve is added so work port flow can occur in both directions. The valve typically employs a drain port due to availability of pressure at both working ports of the valve. Without this, pressure can’t decay and gets trapped in the spring chamber, effectively adding to the spring value, raising operating pressure.
So, sequence valves were used for semi-automated functions (typically the circuit function was started manually), but are they still relevant today? You can buy a pressure transducer, tiny PLC and solenoid valve for less than the price of a proportional valve, and your punch press can be operated electronically instead. I have a hard time believing the stand-alone sequence valve, plumbed either inline or on a valve stack, will provide much value over the electronic option. So, is the sequence valve dead?
I’d say for the most part, they are, but with a caveat. They’re still made by the big players in the game, but they’re the least common pressure valve. The industry within which they may survive quite a bit longer, however, is the integrated circuit industry. Cartridge valves used in custom manifolds are a fantastic method to create unique and highly specialized and functional control circuits. Off-the-shelf stack valves can’t provide the versatility and creativity available to designers, especially when space is at a premium.
Load sensing check valves, pressure compensators, multi-function valves and yes, even sequence valves, can all be combined to provide solutions to unique circuit requirements. Most often, these kinds of integrated circuits are required in the mobile machine industry, where the availability of electronics is limited or impossible. Just as hydraulics will always have a place in the mobile machine work, so too will the sequence valve.