Pressure Sequence Valve Training

Sequence valves are used to control the sequence of operation of two or more actuators. For example, in a clamping circuit the first operation is to move the clamping cylinder in at low pressure, to clamp the equipment. Once clamped, the pressure will rise because the cylinders can no longer extend. Next, the increase in pressure switches the sequence valve and this provides flow to the machining head motor to start operating. So we have one operation at low pressure and then a pressure signal to switch in a second operation.

Sequence valves can be used for a wide range of different machines that require two operations switch by a pressure (system resistance) change. Common uses for sequence valves are clamping and unloading circuits.

Sequence valves offer a range of ways to simplify circuits by reducing the number of valves required. Manufacturers have therefore developed a wide range of different sequence valve types to help simplify a wide range of different users' circuits.

Sequence valve design and operation is very similar to relief and reducing valves.

Sequence valve use mostly spool elements, with some poppets, which sense pressure over a set area to move the spool against an adjustable spring. When the pressure reaches a pre-set value it opens a second port to divert the flow.

Sequence valves are available as:

Direct or Indirect Operation Direct operation is when the pressure is applied directly onto the main spool opening area. Indirect is also known as pilot operated or two stage valve, and is when the pressure is applied onto a smaller pilot valve that opens first, and it's output then opens the larger main stage.

NO (Normally Open) or NC (Normally Closed) designs NO valves are open i.e. allow free flow in their normal, inactivated condition. NC valves don't allow free flow in their normal, inactivated condition but will once they are activated.

2 or 3 way options A 2 way valve will have a single inlet and outlet line. It will almost certainly require additional pilot feed or drain lines as well. A 3 way valve will have 1 inlet and 2 outlet lines, they may also have additional pilot feeds or drain lines.

Internal or External Pilots and Drain Lines An internal pilot is when the pressure signal to switch the valves is taken from the supply or load lines of the valve. An external pilot is when the pressure feed come from a separate part of the circuit via a separate connection. Drain lines may also be internal or external. An external drain will almost certainly be required if you don't have one line that returns back to tank. Without a constant, zero, reference feed the set pressures will fluctuate up and down depending on whatever line pressure they are referenced to.

Each of the above features will provide different performance characteristics

Kick-down valves are sequence valves but have a low bypass pressure drop when open.

Sequence valves are mainly available in cartridge format and while platen-mounted or line-mounted options are available, these tend to just have the same cartridges inside. The reason for this is that one of their key benefits is their ability to allow designers to reduce the numbers of valves in a circuit and if designers are trying to achieve this then they are probably already creating small, more compact custom designed manifolds.

There are a wide range of different options available, each of which will exhibit slightly different performance characteristics. These variations include direct or indirect operation, NO (Normally Open) or NC (Normally Closed) designs, 2 or 3 way options, internally or externally piloted and/or drained connections.

Sequence valves may also be known as pressure sequence valve or a kick-down valve, or by the name of the function they facilitate such as an unloading valve.

Learn more about sequence valves in our 'Professional Training Section'. Understand their design features, performance limits, and how to specify sequence valves.