This commercial grade Spin-Loc with flush valve is used for automatic flushing of the 3/4” drip tubing at the beginning and the end of the irrigation cycle. At the start up of the system, when reaching 0.6 GPM, the flush valve closes, and when pressure drops below 1 PSI the valve opens. To use this Spin-Loc fitting, push the drip tubing over the barb with the "O" ring and thread the sleeve over the drip tubing to secure. The tight seal for the Spin-Loc fittings is ensured by the rubber "O" ring on the barb, which provides a quality water-tight connection.