A cheay eBay generic quick exhaust valve with the rubber piston replaced with a Delrin disk with a light spring behind it and an equally cheap eBay generic pop-off safety valve to provide a full auto cycle. Rate of fire is adjusted by regulating flow to the valve.
The pressure in the pilot area reaches the pop-off pressure of the safety valve, when this actuates the pilot is emptied and the QEV fires, then resets allowing the cycle to start over.
