WHALE Grooved Pressure Switch. Switches the pump on or off by detecting the change in pressure in the water system. Fitted in-line, the Whale Pressure Switch provides a simple and convenient way of creating a pressure system with an electric pump that does not have its own switch. The Pressure Switch is normally fitted close to the pump on discharge side (before any in-line Y piece). The Pressure Switch detects the opening and closing of any tap in the system. An in-line filter is recommeded on the inlet side to prevent dirt from entering the pump or switch.