Aquatec's PSW tank pressure sensing electrical switches are intended for in-line mounting as close to the hydropneumatic product water tank as possible. Its purpose is to turn off the cut off electrical power to the booster pump when the closed source reaches its desired back pressure. The normally closed switch can be factory pre-set at various shut-off pressures. The PSW is available for either 1/4" or 3/8" tubing. When installingg this with a hydropneumatic shut off switch on a reverse osmosis system, use a PSW 40 PSI switch otherwise the system will not shut off properly. PSW240-00 is comparable to the Shurflo 94-090-01 and the PSW340-00 is comparable to the Shurflo 94-090-02. Choose a shut-off switch according to the pressure that works for you. Features: Inexpensive Compact High reliability 100% factory tested