2 - TCA spa

With a direct acting sequence the greater the flow throughthe valve, the further the spool has to move back againstthe spring. This requires an increase in inlet pressure thatcorresponds to the extra compression of the spring.2) Pilot Operated Sequence valve. (1PS60): As with pilotoperated relief valves, the pilot operated sequence valvedoes not require much increase in pressure differential topass more flow. This makes the valve more suitable forvarying flows and systems where the setting has to be closeto the maximum working pressure.In this case the inlet pressure acts on the pilot seat areaand eventually causes the ball to move back against thespring. This creates a flow to tank via the drain port. Theinitial flow passes across the small orifice in the main spool,causing a pressure imbalance that moves the main spoolback against a light spring. It does not take much pressureincrease to move the spool fully back, so the valve willtherefore go from fully closed to fully open over a very smallpressure increase. One disadvantage with this over thedirect acting valve is the constant flow to tank through thepilot section of the valve.3) Unloading Sequence Valves (1UPS100): Most sequencevalves need to maintain a higher inlet pressure than the setpressure to keep the valve open. This, in some cases, canbe inefficient especially if the second operation is working ata lower pressure than the setting....a look at the make up of this devicereveals that it is no more than a logicelement with an adjustable springforce keeping it closed.So much for boring descriptions! The fun part is makingthem do what you want: The standard circuit shown in alltechnical training manuals is the Guillotine circuit (figure 6).The modern version of this machine used for cutting metalrelies on the sequence valve to make sure that the clampsremain on while the knife does it's job.Variations: This is valve use according to the description in themanual. But a look at the make up of this device reveals that itis no more than a logic element with an adjustable spring forcekeeping it closed.The unloading sequence valve allows the valve to open fullyas soon as the setting is reached. The valve functions toopen in a similar way to the pilot operated valve except thatwhen the setting is reached, the spool moves back andopens a separate hole, beyond the control orifice, in thespool to the outlet port. This means that the pressurebehind the main spool will fall to the downstream pressure.The inlet pressure will then fall to the same pressure plusthe pressure required to push the flow across the valve.This can be more efficient than the standard valve.4) Sequence Valve with Reverse Flow Check (1PSC100): Itis usual in a double-acting system for the flow to have topass past the sequence valve in reverse direction. It ispossible to mount a free-flow check valve around thecartridge but it is also possible to include this extra valve inthe design. This cartridge includes the free-flow check,making giving a more compact solution.5) Direct Acting Sequence Valve with Reverse Flow Check(1PSC30): For smaller flows, it is possible to have directacting sequence valves with free-flow checks as standard inone cartridge. This valve is based on the overcentre valvecomponents.