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.

sequence-unloading-group

 

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.

 

sequence-unloading-direct-acting

 

 

 
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.
  sequence-pilot-operated 
     

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. 

 

sequence-kick-down 

 

 

 

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. 

 

sequence-unloading-valve 

 

Common applications for unloading valves include:

Pump unloading in an accumulator charging system

 

sequence-accumlator-charging

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

 

sequence-accumlator-charging-pilot

Pump unloading in a 2 pump high-low circuit

 

 sequence-high-low

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

 

sequence-clamp-lift
  • 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.
  •  
sequence-as-relief

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