Temperature and pressure: how they affect seal life
Every seal has temperature and pressure limits. Exceeding them, even with short peaks, drastically shortens its life. Here is how to read these limits and protect yourself.
On product pages you will often find indications such as "°C −30 +110" or "pressure: depending on working conditions". This is valuable information, but it must be read correctly. Temperature and pressure do not act separately: together with speed, fluid and clearance between parts, they determine how long a seal can do its job.
Temperature
Too hot
High temperatures accelerate the ageing of elastomers. The material hardens, loses elasticity and can no longer follow the surfaces: sealing decreases and cracks appear. In addition, materials become softer when hot and therefore more prone to extrusion. Remember that the temperature that matters is not just that of the oil in the tank: in the sealing zone, friction can generate extra heat, especially at high speeds.
Too cold
At low temperatures elastomers stiffen. A seal that seals perfectly at room temperature can leak when starting a machine that spent a winter night outdoors. Some materials, such as silicone, keep their elasticity better in the cold; others, such as FKM, are stiffer.
How to choose
Consider the real temperature range, from cold start to the hottest working conditions, and choose a material that covers it with some margin. Temperature indications for individual products are shown on our website; the values are indicative and also depend on the fluid and other conditions.
Pressure
Nominal pressure and peaks
A system's pressure value is only part of the story. Load shocks, rapid valve closures and abrupt movements generate pressure peaks that can greatly exceed the nominal value, even for fractions of a second. It is precisely these peaks that damage seals.
Extrusion
Under pressure, seal material tends to be pushed into the clearance between metal parts (for example between rod and head). If the gap is too large, the pressure too high or the material too soft, the seal edge gets pinched and tears off in small pieces. It can be recognised by a frayed edge on the side opposite the pressure.
To counter extrusion you can:
- use harder or composite materials (polyurethane, filled PTFE);
- add back-up rings;
- check the clearance: worn guides increase the gap on one side;
- choose profiles designed for high pressure.
The combined effect
Temperature and pressure influence each other: when hot, the material is softer and extrudes more easily; at high pressure friction increases and so does heat. Add rod speed and oil quality and you understand why two apparently identical cylinders can have very different lives.
Practical tips
- Measure or estimate the real oil temperature during the heaviest work.
- Check the relief valve settings and whether there are shocks in the work cycle.
- Check the condition of the guide rings: uneven clearance encourages extrusion.
- Examine dismantled seals: frayed edges indicate extrusion, hard and cracked material indicates overheating.
- If conditions are at the limit, choose materials and profiles with a larger margin.
If you work in special conditions (high temperatures, intense cold, high pressures or frequent peaks), write to us: we will help you choose among the profiles and materials available in our catalogue.
Frequently asked questions
How do I measure the real oil temperature?
An infrared thermometer pointed at the cylinder tube or tank during the heaviest work gives a good indication. Remember that the temperature in the sealing zone can be higher.
Should back-up rings always be fitted?
No, they are needed when pressure, clearance and material require them. But if dismantled seals show frayed edges, they are often the simplest solution.
Can cold cause leaks only at start-up?
Yes, this is typical: when cold, the elastomer is stiff and seals less well; once the system warms up, the leak may disappear. If it happens often, consider a material with better low-temperature performance.
