Here is a description for one I found. "Flojet's unique Variable Speed Drive system needs no pressure switch. Its microprocessor provides precise speed control to match the system demand. As more water is needed, the motor drives the pump for more flow. As the demand lessens, the motor slows to a super-quiet speed, yet maintains a steady pressure. The result is an unbelievably home-like flow. This smooth performance from no flow to maximum flow is sensor controlled, without any cycling - so an accumulator tank is not needed. The system is free of pulsation, water hammer and temperature swings. Amp draw reduces as flow reduces to conserve energy, ranging from less than 1 amp to a max.of 10 amps"