Pump Coupling Rods: Common Issues and RemediesDecember 13, 2018
It's strange to see a drive system operating properly, yet the pumping mechanism is sitting idle. The prime mover is working, but the fluid impeller has stopped spinning. Clearly, the pump coupling rods are damaged. There's no meshing of parts going on between the two pumping assemblies. Turning everything off, the system switches over to a standby device. The situation is remedied, at least for the moment.
What Is A Pump Coupling Rod?
In some pumping mechanisms, the drive shaft passes through the electric section, through a sealing gasket, and it ends up in the volute chamber. It's in here that the electric motor sends energy to the impeller. Elsewhere, pumps are split in two. There's the prime mover, the electric or fuel-driven motor/engine, then there's the pump assembly. That's how helical rotor pumps operate, via a set of coupling rods. Spliced between the motor and the cylindrical stator/rotor housing, the couplers transmit rotating momentum as raw system torque.
Troubleshooting Coupling Rods
Material flaws are possible, although increasingly unlikely. The forged pins could be marred by a microcrystalline defect. The flaw is invisible. As soon as a fluid transmission spike or system clog occurs, fractures occur and the pump coupling rods break. If there are no cracks and the pump is still struggling bravely to keep up with the motor, consider a misalignment issue. Bearing failure is also likely in this situation. The angularly skewed shaft exerts thrust force, so bearing noise and heat is kicked out by the coupler. The parts wear at an accelerated rate.
Fixing Malfunctioning Drive Couplers
First things first, check the two pump sections. If the motor checks out and the helical pump, stator and all, is still operational, the problem is located inside the coupler rods. By a process of elimination, that must be the system culprit. Focusing on the pump coupler rods, gingerly touch the housing. Is it running hot? Is there an ear-splitting shriek every time the pump starts? The bearings are suspect, or there's a shaft misalignment problem. Grease the bearings, and replace them if necessary. Shim the coupler mounts, and correct the shaft misalignment error.
Sometimes the equipment design process goes wrong. Lots of attention was reserved for the helical pumping equipment. The rotor and stator package has been professionally selected and expertly installed. It's the same with the motor, which provides plenty of torque. Unfortunately, the design process might just neglect the pump coupling rods. When this happens, steady-state torque ratings and start acceleration forces are assessed incorrectly. Always reserve plenty of engineering expertise for the coupling stage so that the properly sized fixtures are correctly installed.
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