Fun With Hydraulics - Auto-Cycle Valves

Auto-Cycle valves can be a real time saver... and they are pretty neat, to boot. The concept is that one operation starts and ends the whole cycle. In the typical system, you have to hold the valve in position on the extend stroke, and then reverse the flow to retract your cylinder. With an auto-cycle valve, the extend works just like the retract AND it automatically starts the retract phase.

Prince Manufacturing makes a darn good RD5000 Series Auto-Cycle valve. Here's how it works:

1. Pull both handles and the cylinder begins to extend.
2. When the cylinder reaches full extension, the pressure builds to the point of engaging the pressure-release detent (also found on standard logsplitter valves) which springs the first handle back to neutral.
3. The second handle still being engaged forces fluid to the retract side of the cylinder, causing the cylinder to return itself to the closed position.
4. When the cylinder reaches fully closed, the pressure build-up engages the aforementioned pressure-release detent, which disengages the second handle. Cycle done.
   

I recently discovered that this can also be done in circuits using hydraulic solenoid valves, simply by using pressure switches and relays. Using one pressure switch on the extend and one on the retract (using relays to lock-in the signal) you can alternately engage the opposite sides of the valve.

1. Engage the cycle by starting the Extend function
   
2. When pressure builds to the pre-determined level, the pressure switch will output a signal, which disengages the relay and engages the retract function (and it's relay)
   
3. When the cylinder fully retracts, pressure is builds to the second preset level, and the second pressure switch sends the signal to disengage the relay. The cycle is over.

This is remarkably useful on splitters, crushers and anything else that can be left alone to do its job.