WHAT ACTUALLY IS AN ACCUMULATOR TANK (AND WHAT DOES IT DO)? Most people know that a water pressure system relies on the presence of an accumulator tank to function properly but few actually understand what it does. They function on the principle that air will compress under pressure whilst fluids will not. An accumulator is an air filled tank that half fills with water as the pump operates. When the pump is turned off the system has a store of water in the tank which is under pressure from the compressed air. This means that, depending on the size of the tank, you can run off a quantity of water without the pump needing to cut in, particularly handy if the pump is installed immediately below a bunk occupied by a tired crew member! Accumulators will also release their store of pressurised water if demand on the system exceeds pump capacity, the larger the tank the more water in reserve. Finally, the air acts as a cushion, absorbing pressure fluctuations and vibrations. This quietens the whole system and allows the pump's pressure switch to reach cut-off pressure cleanly, lengthening pump, motor and switch life. Where a boat has a simple tank without a bladder to separate the air and water do remember to drain the tank down at least once a season, the air tends to get scoured out and eventually the tank will be full of water and serving no useful function at all! TROUBLESHOOTING A WATER PRESSURE SYSTEM Marine water systems are now more technically advanced than ever and should give many years of trouble-free life. However, problems can occur and the following guide to some common complaints may help: FAILURE TO PRIME can be caused by an air leak in the intake or discharge line, a blockage in the inlet pipework, punctured diaphragm, debris under the valves or a crack in the pump housing. PUMP FAILING TO TURN ON can be caused by poor wiring or loose connections, blown fuse, or defective pressure switch or motor. Check that there is full voltage available at the pump before investigating other causes. A PUMP FAILING TO TURN OFF is normally because the switch cannot reach its cut-off pressure. This can be caused by simply having an empty water tank but other causes can be a punctured diaphragm, debris under the valves, leaking pipework, insufficient voltage or a defective pressure switch. Clean inlet filters and check valves and diaphragms, if they are worn now is the time to replace all wearing parts. PUMP CYCLING ON AND OFF WHEN NOT IN USE is most commonly caused by small leaks in the pipework or a tap left dripping allowing the pressure to slowly reduce to the pump's cut in point. Tighten all loose connections after racing the source of the leak. PUMP CYCLING ON AND OFF DURING USE is normally caused by a restricted delivery, check and clean filters and all pipework for restrictions to flow including undersized pipe. Fit an accumulator if one is not fitted. LOW FLOW AND PRESSURE may be just that the pump is undersized for the system. Check the manufacturer's recommendations. However, deteriorating pump performance can be caused by an air leak at the pump inlet, accumulation of debris or scale within the pump and pipework, worn valves and diaphragm, low voltage or defective motor. Low voltage due to inadequate cable size being used is a common cause of pump problems, always follow the cable size recommended in your data sheet. Checking that correct voltage is available can only be done by measuring voltage at the pump when it is running. INCREASE THE LIFE OF YOUR WATER PRESSURE SYSTEM Most boat owners leave their boats at the end of the weekend and sensibly turn off power to the pump. However, pump life can be increased by also opening the taps to relieve pressure in the system once power is off. This depressurises the system saving wear and tear on diaphragms and valves when not in use.