Marine screw pumps mainly include: marine single screw pumps, used for bilge sewage transfer and 15ppm bilge water separator; marine twin screw pumps, used for transporting light diesel oil; and marine triple screw pumps, used for transporting lubricating oil. Therefore, its daily maintenance is very important.
①Though screw pumps have self-priming ability, we should still prevent the pump from running without any liquid in. There will be serious friction loss under this condition. Therefore,a screw pump should be filled with liquid before starting first time or just after an overhaul.
②When delivering clean liquid, triple-screw pumps have to be fitted with a 40 ~60 mesh filter which should be cleaned periodically. For a new piping system, solid impurities, such as rust, should be removed thoroughly. Should any abnormal noise found, the pump be turned off immedi-ately and inspected.
③Generally,screw pumps have their own designed rotation direction. If the pump rotates in opposite direction, the suction and discharge direction will also be reversed, thus the axial-force balance device will lose its function.
④The discharge and suction valves should be fully opened when starting the pump. The pump can not run for a long time with closed discharge valve. Moreover,a small flow rate should not be achieved by means of bypassing most of the discharge liquid through pressure adjusting valve. Because nder this situation, there will be a serious throttling losses and thus the temperature of liquid will be greatly increased,which might make pump deformed or damaged.
⑤Attention must be paid to avoiding bending of the screw since the screw is long and not strong enough. For a large pump,the center line should pass through the rib of the ship. The piping system should be tightly fixed and well aligned with the discharge and suction ports of the pump. For storage,it should be fixed vertically to avoid bending. During operation,oil temperature should be controlled because the screw may expand and become bent under high temperature.
⑥Cavitation, which may result in noise and vibration,may be caused by low oil temperature, high viscosity,clogged suction strainer and air entrained in the oil. In addition, poor alignment and too much wear will also cause noise and vibration.
⑦Mechanical sealing, which is a precise component, should be carefully handled when dismantled. When reassembling the mechanical sealing, there should be lube oil on the shaft and sleeve. After installation, tightness of the rotating ring should be checked to see if it can meet the requirement.
