Why Shore A Hardness Changes Pump Flow More Than Wall Thickness
Two tubes, same ID, same wall, 12% different flow rate. The variable was hardness — and it is usually the last thing specified.
Hardness is a flow property, not just a feel
In a peristaltic pump the tube is the pump chamber. It has to collapse fully, then recover fully, thousands of times an hour. A harder tube resists collapse and gives up stroke volume; a softer tube recovers slower and starts to creep.
The numbers
| Shore A | Flow vs 50A baseline | Tube life | Typical use |
|---|---|---|---|
| 40A | +6 to +9%% | Shorter, wall thins over time | Shear-sensitive fluids |
| 50A | Baseline | Balanced | General metering |
| 60A | +3 to +5%% | Longer | Higher pressure, viscous media |
| 70A | -4 to -7%% | Longest | Pressure lines, low pulsation need |
The counter-intuitive part is the middle of the curve. Going softer increases stroke volume but loses it again to creep; going harder keeps shape but sacrifices fill. 50–60 A is the plateau for a reason.
What else moves when you change hardness
- Barb retention. A 10 A drop needs a bigger barb or a clamp.
- Suction collapse. Softer tube collapses earlier under vacuum.
- Sterilization. Steam cycles soften low-hardness compounds more.
- Cost. Hardness itself is nearly free; the compound changes behind it are not.
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Questions about your own part?
Send a drawing or a sample. We will tell you which compound and hardness we would run, and what it costs at your volume.