23 February, 2020

Open end to atmosphere

20 June, 2014

At the recent Air-Tech exhibition at the NEC in Birmingham, Beko Technologies gave a presentation about the issues of having an air supply at, for example, 7 bar (g) venting down to atmosphere without doing any useful work or work that cannot be done more economically or safely by another medium… An example of this would be the use of blow guns to clean machinery down at the end of a production period i.e. could be three times per day. This practice was widespread and was wasteful in that the dirt/dust would resettle, the pressure was not often regulated and it is a potentially dangerous practice particularly if the operative has an open sore then compressed air can be potentially lethal. There is a simple answer, use a vacuum attachment to the airline or a ‘venturi’-assisted type which increases the flow at reduced pressure. The opportunities for saving were broken down into 3 key areas. The first was leaks and it is well-known that leaks from a compressed air system can be quite considerable. In fact, a system with 10 per cent leakage is regarded as a good one. Bearing in mind that 10 per cent of all power used in modern industrialised societies will be to compress air then we are wasting 1 per cent of all power even when we are good at housekeeping so it is clearly important that we make sure that the wastage is not significantly higher than this. Causes of leaks What causes leaks in a compressed air system? There are many opportunities for the compressed air network to develop leaks but the principle ones would be: • Corrosive condensate. The particulate material drawn into a compressor together with the small amount of oil carried over will become an acidic liquid when the compressed air cools and water vapour condenses out and mixes. • Poor installation. Pipe supports not adequately deigned causing stress on joints which become leaks. Cheap solutions such as hoses for temporary solutions which become permanent. • Impacts such as fork lift truck. • Poor maintenance. The maintenance engineer has to see the compressed air network as a part of his maintenance routine rather than a one-off occasional exercise to cull leaks. Also some machinery will be stopped at a point where a valve or orifice is open and will remain open until the machinery restarts. These may be small occurrences but the sum total of all these small leaks is normally in excess of 10 per cent and for example a 75kW compressor running on load for a year will cost more than £70,000. Therefore it is important to check leaks via an ultrasonic device, mark up the leaks in some kind of classification as to the severity of the problem then fix the worst ones. It is then important to realise that this is not ‘job done’. The leaks will in some cases come back because of poor installation or appear elsewhere as the corrosive condensate or an impact creates a new leakage. The second area is condensate draining and it is important to understand that the condensate has to be drained efficiently or can be re-entrained and cause moisture problems and as just indicated will create leaks in the distribution system. There are not too many old fashioned steam type traps used anymore because they were subject to blocking through debris falling onto the valve seat and also to hydraulic locking requiring the installation of a balance pipe. Solenoid drains became popular and are still widely used but are inefficient because of the number of variables involved such as compressed air flow, pressure, temperature and relative humidity.

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