Application Notes
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comatrol hydraulic cartridge valves

As the name implies, sequence valves control a sequence of operations. Sequence valves usually use a pressure signal to shift a spool, thereby opening or closing a flow path at a pre-set pressure.



Direct-Acting Sequence Valves

Direct-acting sequence valves are spool type valves with a spring force holding the spool closed.

When inlet pressure exceeds the spring setting, the spool shifts to direct flow to a second function. 

Direct-acting sequence valves come in a variety of configurations:

  • Internally-piloted with external drain

  • Internally-piloted with internal drain

  • Externally-piloted with internal drain

Direct-acting sequence valves are best suited for fairly constant flow and lower pressures.





Pilot Operated Sequence Valves

Also available are pilot-operated
sequence valves that have an internal pilot and an external drain.

Pilot-operated sequence valves are best suited for higher and more widely varying flows, and higher pressures.

Kick-Down Sequence Valves

Another type of pilot-operated sequence valve is commonly known as a kickdown sequence valve. The kick-down sequence valve blocks flow at 1 until sufficient pressure exists at 1 to force the pilot poppet off it’s seat. This creates a pressure differential across the spool that causes the spool to shift and open flow from 1 to 2. The spool will remain open until flow through the valve is shut off.

A common application for a kickdown sequence valve is as a safety device in circuits where overloading or overheating could cause damage if pressure is held for an extended period of time. 






Unloading Valves

Another type of sequence valve is commonly known as an unloading valve.  The unloading valve blocks flow at 2 until sufficient pressure exists at 1 to pilot the poppet open against the pre-determined spring setting and allow flow from 2 to 3. If the pressure at 1 drops below the pilot ratio value multiplied by the predetermined spring setting the valve will close, blocking flow at 2.

Various pilot ratio values are available; consult catalog sheets for details.

An unloading valves is typically used to unload a pump outlet to tank at a minimum pressure drop, resulting in higher system efficiencies with less heat generation. 




Common applications for unloading valves include:

Pump unloading in an accumulator charging system



For higher flow rates the unloading valve may be used to pilot a larger logic element



Pump unloading in a 2 pump high-low circuit



Both direct-acting and pilot-operated sequence valves have many common applications including:

  • Providing a sequenced series of operations such as in a clamp and lift circuit


  • Use as a relief valve where the return line has high or varying backpressure. The independent spring chamber drain line provides a relief setting unaffected by downstream pressure.

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