Topics - Twin Headed Pump
Twin Headed Pump
Pumps used in liquid chromatography are required to deliver very constant liquid flows, free of pulses, at extremely high pressures. The early piston pumps had stainless steel bodies and carefully ground sapphire pistons. Their exit flow was controlled by a non-return valve and the pulses were reduced by employing carefully contoured cams that drove the pistons. The cams were cut so that the liquid was delivered at a relatively constant rate and, at the end of the piston stroke, the cam was cut to allow a relatively rapid return and refill. Although this system reduced the pulsing effect, there remained significant pulses in the exit flow from the pump. However, these pulses were further reduced by the introduction of the twin-headed pump. Twin headed pumps were constructed in a very similar form to the single piston pump but the cams were contoured so that the output of one pump always increased rapidly during the refill of the other pump. In this way, with the aid of a pulse dampener, pump pulses were virtually eliminated in the twin headed pump. Rapid-refill pumps also have two cylinders and pistons but they operate in an entirely different way. The cylinders are back to back and one cylinder is used to rapidly refill the other on its refill stroke. In general, the rapid refill pump is not as pulse-free as the twin headed pump.