The SCWD (pronounced "squid") is a revolutionary device designed to provide alternating currents without the use of electricty. The SCWD mounts inline with 3/4" tubing, the two ports alternate the output, the bottom port is the input. A great alternative to expensive electronic ball valves. The SCWD will run on any pump with a minimum output of 50 GPH and a maximum output of 1400. The switching speed and current duration is dependent on the volume of water flowing through the SCWD. You can control the duration by controlling the flow going through the SCWD. Can be submersed for use with large power heads or used externally.