How vibration isolation works (explained simply)
Updated : · Piscines VP
To isolate vibration, the support must be soft enough for the pump to 'float' on it: its natural frequency must be much lower than the motor's frequency. A thin, hard mat is too stiff and passes almost everything. A well-chosen support compresses a few millimetres under the pump's weight and cuts most of the vibration.
Putting “a piece of rubber” under a pump seems logical. Yet it often does almost nothing. Here’s why.
A pump is a mass on a spring
When you set a pump on a soft support, it behaves like a mass on a spring. That system has a natural frequency: the rate at which it would bounce on its own if pushed.
- Very hard support (concrete, thin rigid mat): very high natural frequency. Pump and slab move together. Everything passes.
- Well-chosen soft support: low natural frequency. The pump “floats”. The motor’s much faster vibration barely gets through.
The golden rule
Isolation starts working when the motor’s frequency is more than about 1.4 times the support’s natural frequency, and becomes really good when the gap is large (3, 4, 5 times or more).
A pump at full speed turns at about 58 revolutions per second (58 Hz). At low speed, a variable-speed pump can drop to around 17 Hz. To isolate well at low speed too, the support needs a very low natural frequency, so it must be soft enough.
How to recognize it
A good support compresses a few millimetres under the pump’s weight. A support that doesn’t move at all is too hard to isolate. One that compresses too much makes the pump unstable and stresses the fittings.
The danger of resonance
If the motor’s frequency lands close to the support’s natural frequency, it’s worse than no support: vibration is amplified. That’s why a support must be designed for the pump’s weight and speed, not picked at random.
Summary
| Support | Effect on vibration |
|---|---|
| Directly on concrete | Everything passes |
| Thin, hard mat | Almost everything passes |
| Poorly chosen soft support | Can amplify at some speeds |
| Support designed for the pump | Cuts most of it |
That’s exactly the problem SOURDINE is working on: a support designed for the real weight and speeds of pool pumps, tested with an accelerometer. Get notified →
Frequently asked questions
Is thicker rubber always better?
Not necessarily. What matters is that the support compresses enough under the pump's weight. A thick but very hard block can isolate worse than a thinner, softer support.
Why is a pump at low speed harder to isolate?
Its frequency is lower and gets closer to the support's natural frequency. The support then needs to be even softer to stay effective.
Not sure of the cause? Take the 2-question diagnosis →
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