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Most hydraulic pumps have light bearings while the electric motors by which they are driven have heavy-duty bearings. This makes it extremely important that the alignment of the pump and motor shaft be near perfect. Angular or offset misalignment always results in pump bearing failure, followed by internal failure soon after startup. Shaft couplings can take care of minor inconsistencies in shaft alignment, but they wear out very soon when not properly applied.
Figure 8-35 illustrates examples of misalignment. When the pump and motor are mounted separately, they must be aligned as nearly perfect as possible. Straight edges, dial indicators, and lasers give accuracy ranging from low tech to high tech, but they are only part of the answer. The pump and motor must sit on a rigid base and must be held down with ample force so they do not slip around during operation. The best alignment job possible can be rendered useless by inadequate mounting hardware.
A simple way to overcome alignment problems is to use the pump-motor adapter shown in Figure 8-35. The pump-motor adapter is attached to a “C” face electric motor that has a flat-machined face and pilot protrusion. This face and pilot are perpendicular to the shaft and concentric to very close tolerances. A matching pilot and face are machined on the pump. The pump-motor adapter has matching machined faces and pilot bores. It is purchased for a particular motor and pump, so it is the right length for the shafts specified and matches the motor and pump mounting flanges. When this assembly is bolted together all parts align perfectly.
The shaft coupling then is slipped together and its setscrews tightened through the access port provided. The motor can be mounted on almost any surface without a chance of misalignment, and the pump can be changed without alignment problems anytime or place. Always use a coupling guard with an open coupling arrangement. Install the access-port cover before operating the pump when using the pump-motor adapter setup.
Figure 8-35 also shows the correct way to drive a pump with a belt. Light bearings on the pump cannot stand the side loads from belts so the pump fails very soon. Use pillow-block bearings to take the side load and couple the pump to the bearing guided shaft. This arrangement gives long service in applications where belts must be used.
Testing a pump
Figure 8-36 shows a typical setup for testing a pump that is suspect, has been out of service, or has been rebuilt. The flow meter could be an added device if the unit does not have one. It could be part of a test stand setup but is a necessary item when checking pump efficiency. The loading valve could be a ball valve as shown in the figure or another type valve as long as it can take the maximum pressure it will see. The relief valve must be in place and set for maximum rated pressure or operating pressure as needed. A pressure gauge is required to indicate system pressure. The filter should be part of a standard hydraulic power unit, but would usually be an off-line setup on a test stand.
To test a pump, lower the relief valve pressure setting to minimum. Then start the electric motor and check for flow on the flow meter. The meter should read at or very near catalog rating with all flow going directly to tank.
If the meter shows the pump producing ample flow, start closing the loading valve and watch the pressure gauge as it climbs. The reading should be low because the relief valve is set low. When the loading valve is closed completely, reset the relief valve to test pressure and observe the flow meter. Flow will drop somewhat, depending on the type of pump being tested. Most manufacturers publish rated flow at pressure in their literature. If the flow meter reads at or near cataloged rated flow, the pump is ready to put in service. If not, the pump should be checked or rebuilt to bring it up to specification.
Chapter 18 covers air- and hydraulic-driven intensifiers or boosters, which technically are pumps. These units usually are associated with air-oil systems. That is why their descriptions are in Chapter 18.
Air-to-hydraulic intensifiers are 100% efficient in the hydraulic end and are pressure compensated. They usually produce low volume so they are not normally used as a system’s prime mover. Their main advantage is they can hold pressure for long periods without generating heat or consuming energy. (Check out Chapter 17 to learn more about this unique pumping system.)