By Colin Rice of Colin Rice Exploration and Training (Pty) Ltd
When an air hose or a fitting on an air hose fails, the air that escapes expands extremely rapidly and causes the air hose to move in the opposite direction at substantial speed. In this article, I will examine the magnitude of the force that the escaping air exerts on the air hose.
This is the first article of Part 2 of our Technical Series on Compressor and Air Hose Safety. Click here for an outline of the entire Compressor and Hose Safety Series.
An air hose contains air under significant pressure and when the hose or a hose connection fails, the pressure on the air is suddenly released and this causes the air to suddenly expand. The rapidly expanding air flows out of the hose at high velocity and this causes the air hose to whip violently.
The escaping air exerts a force on the hose or fitting which will cause the hose to travel in the opposite direction to the path of the escaping air and it is useful for us to get an understanding of the magnitude of the force that is exerted on a hose when it fails. To do this we consider an air hose of internal diameter d mm under a pressure of P bar. In this case we can say that the force, F, that would be exerted on the air hose in the event of a catastrophic failure can be estimated as follows:
Example: Assume a 50mm air hose under 24 bar pressure;
This calculation shows that should a 50mm air hose under 24 bar pressure fail, it will be flung backwards with a force equivalent to 500 kg. In addition, the rapidly expanding air escaping from the hose will cause the hose to travel at considerable speed and so the momentum of the hose will be substantial. These two elements form a potentially lethal combination and so appropriately restraining high pressure air hoses is a critical element of any safety management system.