An element of the GARDENA Sprinklersystem, the GARDENA Drain Valve prevents frost damage to the system installed underground. This takes place through automatic drainage when the system is taken out of operation; the valve opens when there is water pressure of under approx. 0.2 bar in the system. Drain Valves should be installed at the lowest point of the irrigation system and, for safe drainage, installed in a pack of washed coarse gravel. It has a 3/4" thread.