Multi-Chamber Diaphragm Pump, AD4/90 and AD550 AQUATEC For transfer, demand delivery, filtration, high flow booster, beverage dispensing and continuous reverse osmosis applicationsSpecific gravity: 30 maximumSelf priming (up to 2m head)Quiet and energy efficientIngress protection to IP44AD4/90 continues to run in closed valve conditions liquid being re-circulated via an internal bypass valve, AD500 ceases to run in closed valve conditions as it is fitted with a pressure switch