Solenoid/electronic diaphragm pumps are the diaphragm pumps with the fewest moving parts. Timing circuitry energizes an electromagnet, which slides the diaphragm into the discharge position. The magnet moves against both back pressure and a spring. When the magnet is de-energized, it drives the diaphragm mechanism backward into the suction position. A system of check valves keeps the fluid flowing in one direction. Solenoids can pump against a dead head (infinite backpressure) because they are designed so that the electromagnet cannot force the diaphragm to move against a back pressure that exceeds its burst pressure. Since magnets can be built only so large, the practical limit to flow and pressures regimes for these pumps is 20 gph at 30 psi.