Features: Inexpensive Compact High reliability 100% factory tested Built-in John Guest half cartridges 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 Booster Pump when the tank is full. The normally closed switch can be factory pre-set at various shut-off pressures. The PSW, when used with a typical under-counter RO system, enables the hydraulic shut-off valve to open and close very reliably and positively. The PSW, with two John Guest half cartridges, is available for either 1/4" or 3/8" tubing. Optionally available are 1/4" or 3/8" Jaco elbows. When both the permeate pump and a 6800 or 8800 series booster pump are used together or the tank switch psi is above 40, an electronic shut-off valve must be used with the PSW tank switch. If an electronic shut-off valve is not used when the PSW tank switch is above 40 psi, the water will never get shut off and the system will continue to run.