Softer strokes give quieter operation

Tom Shelley visited Hampshire to listen to a quiet pump specifically designed for the needs of the medical market

Pnuematic pumps have been developed which, thanks to the use of deliberately soft pumping strokes, keep sound levels down to well below 40dB(A) at 1m. Primarily designed for the medical market, they incorporate design principles applicable to any kind of quiet operating fluid pumping operation. The Aims pump is the brainchild of Mike and Steve McGrath, proprietors of Archfact, a well established engineering subcontracting firm based in Waterlooville, Hampshire. Steve told Eureka that the idea arose following requests from customers who have to import such products from overseas leading to long lead times. One specified application was the provision of air for ripple beds. Concepts that arose from the project include a number of patented innovations. The most important one being that the pumps are mains-powered reciprocating solenoid pumps, but with power only applied on the induction stroke. At the same time as air is drawn in a return spring is compressed, the power stoke is then effected by the spring, whose force decreases as the piston shaft is pushed forwards. The net effect is that the power stroke is ended as gently as possible, preventing the creation of pressure pulses that might, in turn, give rise to noise. The drive coils, placed each side of the armature portion of the piston, are directly powered by half-wave rectified mains power. The armature part of the piston is drawn into the space between the coils during powered half cycles and the spring pushes the piston back between the half cycles. Incoming air is filtered, drawn in through an orifice and passed over the coils cooling them and reducing noise emissions both from the coils and the input side of the cylinder. Additional aids to noise reduction include specially developed compound polymer bearing materials and cantilevered soft rubber feet. Various pump models are presently available. High flow pressure versions, suitable for applications such as ripple beds, produce air at up to 0.5bar while higher pressure versions, suitable for heart assist devices and deep vein thrombosis therapy pads, deliver air at up to 4bar. Mains supply can be 50 or 60Hz, 115 or 230V, maximum flow is 15litres/min while maximum pressure is 4.5bar. Coming in at 92 x 58 x 58mm, prices are less than £100 for one-offs with substantial reductions for quantity orders. All products conform to UL and CE requirements. Versions with flow rates of up to 50litres/min, able to deliver pressures of up to 5 or 6bar, are in preparation. The pumps operate substantially below 40dB(A) at 1m Flow rates are up to 15l/min and maximum pressure is 4.5 bar