Bursting pressure and working pressure
– finding the right polyurethane tubing part 2 –
Overview of the article series:
- Polyurethane resistance against environmental influences
- Working pressure and bursting pressure
- Flexibility – the minimum bending radius
- The Pricing of polyurethane tubing
Starting with the second part that covers the most important details of to pressure resistance of polyurethane tubing:
Difference between working pressure and bursting pressure
Many manufacturers only state the maximum pressure a tube can withstand in sales. This pressure gets determined by putting the tubing under pressure until it bursts. The evaluated value is the so-called bursting pressure. The question is how this value is applied practically. It may be that the tube can endure short pressure peaks up to its bursting pressure, but it is in no way capable of handling such a high pressure permanently.
In contrast, the working pressure already contains securities. However, there are significant differences from manufacturer to manufacturer. Some don’t even state working pressures. Others are working with triple securities. The differences often get exposed in practice: Those who calculate with too low securities might be able to claim higher pressure resistance on paper, but they get caught up by more failures during the application many times. Generally, the working pressure should get communicated only as high the tubing can endure it under permanent load without issues. A tubing that is made to endure a lot of pressure is the flamex hybrid hd.
Influential factors on the pressure resistance of polyurethane tubing
- The hardness level of the polyurethane: Generally speaking, the harder the raw material of a polyurethane tubing is, the higher its pressure resistance. Naturally, increased hardness means a decrease in flexibility. Hence, the tubing should only be as hard as necessary and as soft as possible. The hardness level of polyurethane typically gets recorded with the so-called shore hardness. The scale starts from shore A (soft) and ends with shore D (hard).
- The wall-thickness of the tubing: A tubing’s wall-thickness has a large impact on its pressure resistance. In general: the thicker the wall, the higher the pressure resistance. As it almost always is, increasing the wall thickness comes at a certain cost. Quite literally, the tubing becomes more expensive due to the increased raw material required for production. Moreover, a thicker wall also decreases the flexibility of the tubing. In the end, the same motto applies: the wall should be as thick as necessary but as thin as possible.
- Adjustment to environmental influences: As explained in part 1 of this series, Polyurethane resistance against environmental influences, external factors such as temperature, abrasion, UV-radiation, or chemicals can negatively impact the pressure resistance of polyurethane tubing. To ensure maximum performance it is crucial to choose the suitable tubing for the purpose.
Working pressure and bursting pressure – conclusion
In short, the working pressure states the stress that tubing can endure in permanent use. On the contrary, the bursting pressure is the maximum load that it is able to withstand for a short time. If the goal is to create pressure-stable tubing, the raw material should be rather hard and the wall rather thick. That is only achievable at cost of other characteristics. Last but not least, the tubing should be tailored to the environmental conditions so that it can show its whole pressure resistance ability. To find the perfect balance between maximum bursting pressure and other mechanical properties, contact your favorite manufacturer!