Calculating compressed air system leakage

[sagaris]

I am looking to quanitfy our compressed air system leakage and have followed the usual steps of ensuring all air consuming products are off and then measuring load/unload times.

I intended to use the following formula as found in relevant articles and webpages:

% Leakage = (Tx100) / (T+t)​

where T = total load time
t = unload time

the problem is that our compressor (an Atlas Copco GA 75) has a load, unload and OFF mode (its NOT variable speed) and the only reference i can find that includes load, unload and off into the calculation quite crudley uses the above equation but bundles load and unload together as 'T' then the off mode as 't'.

doing this puts our losses at 17.68% but i am 99% positive this is incorrect, as we have 375 m of 3inch ring main that has never had any air leakage assesment and you can hear it leaking everywhere now that we are in shutdown and then much more so with our ultrasound equipment! apparently 10-15% leakage for a compressor system of our size is acceptable but this just doesn't seem right?! expected plant losses for somewhere that hasn't had leakage assesment before are typically around the 25-40% range.

the load, unload and off equation completely ignores the fact that load and unload are doing opposite things! the off is merely to save energy where as unload is to regulate the desired air pressure. if anything it should be OFF time and unload time together as at that point the rest of the system is not being fed and only the leaks are affecting the system pressure. But by putting unload and OFF times together means the calculation puts leakage at 7.58%...and that is 100% incorrect! (10% is considered a good level of leakage)

any ideas?

thanks in advance

 

[sagaris]

I should add that the GA 75 (75KW) compressor is one of two and there is an additional 90KW Variable speed drive compressor, so three in all. its just that this is the only time in the year where just one is running so the load, unload and off times can be measured.

with regards to calculating the system leakage it doesn't matter if one or all 3 compressors are running as the reciever is still being filled to the same pressure as during production, with the exception that there is no production load, so just the one can cope.