A diaphragm starts ageing the day it leaves the mould. On a vehicle that ageing is driven by flexing, heat and road spray. On a shelf it is slower, but it does not stop — and a part that has been stored badly can crack on its first application, looking for all the world like a manufacturing fault.
Most of what decides how a diaphragm survives storage is in the hands of whoever holds the stock. Here is what matters.
What attacks rubber on a shelf
Four things, all of them ordinary:
- Ozone. It cracks rubber that is under tension. Electric motors, battery chargers, welding sets and high-voltage equipment produce it, and all of them are common in a parts store or a workshop.
- Light. Direct sunlight and strong ultraviolet sources speed up surface ageing.
- Heat. Warm storage accelerates every ageing process at once.
- Oils and solvents. Some rubber families swell or soften on contact; a diaphragm stored next to a leaking drum can be ruined without ever being used.
Our material guide explains why different compounds respond differently to oil and weather.
Where to keep it
Cool, dry and dark. An interior storeroom away from windows is better than a mezzanine under the roof, and both are better than a container in the yard. Keep diaphragms away from the motors, chargers and welding sets that produce ozone, and away from fuels, lubricants and solvents.
The international guideline for storing rubber products is ISO 2230, and it is worth reading if you hold rubber stock of any kind. We do not repeat its figures here: they are its figures, not ours.
How to keep it
Flat, unstressed and in the carton. Rubber held under tension ages faster, and ozone attacks stretched rubber first. So:
- Do not hang diaphragms on hooks or pegs.
- Do not fold them, roll them tight or force them into small bins.
- Do not stack heavy goods on top of the cartons.
- Keep them in the packaging they arrived in until they are fitted.
Rotate and record
First in, first out. Mark each carton with the date it arrived and keep the batch number visible. If a part is ever questioned, the batch number is where the examination starts — our claims and returns terms ask for it for exactly that reason.
Before fitting a part that has waited
Look at it, and flex it by hand. Signs that a stored diaphragm should not go on a vehicle:
- fine cracks that open when the rubber is bent, especially on the folds;
- a surface that has gone sticky, or one that has gone hard and glossy;
- a permanent crease or flat spot left by the way it was stored;
- any sign of the fabric reinforcement showing through or separating.
If in doubt, do not fit it. A diaphragm costs little next to the labour of opening a brake chamber twice.
What we do not publish
We do not state a shelf life. How long a diaphragm keeps depends on the conditions above far more than on the calendar, and a single number would be a promise about conditions we cannot see. What we can say is that orders are produced against the proforma, so what arrives is current production, with the batch on the carton.