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Couplings under fluctuating torque
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Posted by: ReubenAG ®

09/30/2003, 06:29:03

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I am trying to find what type of coupling handles fluctuating torque best. The application is for a reciprocating piston vacuum pump. The torque required by the pump changes as a function of crank angle (like in a single piston engine). The pump is  driven by a 3 phase 380 Vac motor, with the motor trying to exert a constant torque (I assume). This is resulting in the coupling seeing a torsional vibration. The coupling currently in use is a Renold Discflex. The coupling has failed twice. On both occasions, the flexible element holes were distorted (slotted) by the pins, allowing metal to metal contact between the pins and the opposite couling halves. The pins and couling subsequently failed.

Are there any ideas on a better coupling to use, or alternative solutions?

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Re: coupling a recip.
Re: Couplings under fluctuating torque -- ReubenAG Post Reply Top of thread Forum
Posted by: RKimball ®

09/30/2003, 23:18:57

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You might try a LoveJoy coupling, (two sets of dogs with a urethane or rubber asorber between them).

Also, as you may realize, often it is necessary to add a flywheel to smooth out the torque pulses.

Most cars use a clutch disk with torque take up springs or a hydraulic (torque converter) coupling. There must be give somewhere to take out the harsh torque peaks. Metal to metal won't do.

good luck

** The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, don't fail to listen to suggestions. -randy-

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Re: coupling a recip.
Re: Re: coupling a recip. -- RKimball Post Reply Top of thread Forum
Posted by: hnic ®

11/15/2003, 02:06:25

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Trying to use a coupling to drive a reciprocating load can lead to many problems. I’ve seen where you finally get a coupling that doesn’t break, but then the shaft breaks. What is happening here is the shaft is operating at its critical speed. I will give some things you can try.


First I think running it directly off an electric motor is too fast, the correct speed would have to determined, in consolation with the pump manufacture or someone familiar with type of pump. If you look at shop compressors you will notice that they all use V belts, the reason is that the belts absorb a lot of the vibrations. Also note that they use a heavy pulley on compressor; the reason for is that the pulley is actually a pulley and flywheel in one. I would recommend that you change to a belt drive. You should be able to get a pulley from a compressor repair shop.


If you continue to have problems it would be best to obtain the services of a mechanical engineer familiar with machine vibrations.


Good luck!

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