Jabsco Pump Catalog

DIRECT DRIVES Misalignment between pump and drive shaft is a common cause of pump failure. A flexible coupling is only “flexible” within limitations specified by the manufacturer. Excessive misalignment, particularly at high pump speeds, can cause noise, knocking, vibration, premature bearing failure, usually followed by pump leakage. BELT DRIVES The pump speed is determined by the engine pulley diameter and the need to maintain the pump pulley at a practical maximum size. Some engine crankshaft pulleys incorporate vibration dampening membranes resulting in large diameters at the V-groove. To lower pump speed relative to engine speed, it is necessary to use a pulley on the pump that is larger than the drive pulley. High engine speeds may, therefore, require oversize pump pulleys which preclude the practicality of a belt drive. Calculating a suitable size pump pulley (example): Drive Pulley Diameter ———————————————————— Pump Pulley Diameter x Engine Speed = Pump Speed Excessive drive belt tension will cause rapid belt wear and may result in premature bearing failure. It should be possible to deflect a correctly tensioned belt between pulleys approximately 1/2"–3/4" (13–19mm) by applying finger pressure. While excessive belt tension may be due to inadvertent overtightening, it should always be verified that it did not result from an inherent fault in the installation, e.g., if pump flow is insufficient due to a slipping belt caused by insufficient contact area between belt and pulley, any amount of tightening would not solve the problem permanently. Ideally, the contact area should be about 120° but not less than 90°. If the engine is installed on flexible mountings, a belt driven pump must be mounted on the engine, never bolted to the vessel’s structure. This is to avoid tensioning or slackening of the drive belt due to relative movements of the engine. GEAR DRIVES Drive gears fitted to “heavy-duty” flange mounted pumps are supported by the pump ball bearings and driven by one of the engine gears. CRANK PULLEY MOUNTED DRIVE A number of Jabsco pumps specially developed for high speed operation on gasoline and diesel engines are fitted with a multi-positional bearing housing bolted directly to the crankshaft pulley, thus eliminating mounting brackets, belts and pulleys. As the pump body is supported by the ball bearing only, it must be prevented from rotating by means of a torque arm, designed and installed so as to avoid any side load on the bearing. Inlet and outlet hoses must be flexible, i.e., of adequate length (at least 10 times the hose diameter) so that the pump can be rotated freely over a few degrees by finger pressure only. Pump Drives Crank Pulley Mounted Drive Installation Example Belt Drives Insufficient Contact Area 16mm per Meter of Span Minimum 90º 99 11 Flexible Impeller Pumps Introduction