Rubber-in-compression couplings, from Renold Hi-Tec, are perfectly suited to pumping applications,
particularly when large particulates such as sand or gravel are being pumped. The rubber blocks in the
couplings eliminate torsional vibration, isolate resonance and dampen vibrations in the system that
would otherwise cause early failures.
Torsional vibration is caused by the almost imperceptible pulses in torque that are inherent to
diesel engines and variable frequency drives, which are commonly used to power pumps. Each power stroke of the engine produces a pulse, or peak in torque that causes an indiscernible twisting of the drive shaft that will eventually destroy it if left unchecked.
Each diesel engine also has its own natural resonance, a bit like the note of a ringing bell or the sound of
a vibrating guitar string. If the engines resonance coincides with the natural frequency of the pump then
the results can be catastrophic.
The modern solution is to fit a torsionally soft coupling in-between the diesel engine and the drive
shaft to isolate the engine’s harmonics and torsional vibration from the rest of the system.
Rubber-in-compression couplings are frequently selected due to their failsafe design, which is a
critical requirement in many pumping applications like fire fighting for example.
Rubber-in-compression couplings are made up of two round metal sections with what looks like the paddles of a paddle steamer projecting inwards from the outer section and outwards from the inner. Rubber blocks are placed in the spaces in-between the paddles, and, as the outer section is turned by the engine, the inner section is driven through the rubber blocks. As this happens the rubber is compressed and hence the term, ‘rubber-in-compression.’ The couplings are failsafe because even if the rubber blocks failed the strong metal paddles would come together and continue to drive the pump.
Rubber-in-compression couplings are also maintenance free and do not require lubrication or adjustment of any kind, which means they provide the lowest lifetime cost on all pump applications. The only serviceable item are the rubber blocks, which in most cases are good for over 10 years of service.