Littelfuse Model ALT-100-1-SW Alternating Duplex Pump Relay with Switch 95-125V 11-pin Plug-inLittelfuse ALT 100 1 SW Alternating Duplex Pump Relay With Switch Description The ALT xxx 1 SW ALT xxx 3 SW Series are used to alternate between two loads and are commonly used in duplex pump up and pump down applications to balance the runtime of both pumps. The ALT relays have a built in debounce time delay that prevents the relay from changing state if the float momentarily bounces, and they have a built in switch to manually force a specific load