There remain many myths and much confusion about air
leaks, costs, techniques and so on. Here, in the first of a twopart
article, Chris Dee, executive director of BCAS sets out to
clarify the position

At the very first meeting of the British
Compressed Air Society in January
1930, the cost of air leaks and
associated loss of system performance was
discussed and our first air leak awareness
programme launched. Reducing air leaks is
probably the single most important energy
savings measure, applicable to almost all
systems. Why then, listening to comments
from visitors to the BCAS stand at the recent
Maintec exhibition, are compressed air leak
programmes often ignored or even
discouraged by management?
Awareness of the importance of a regular
leak detection programme is low, in part
because air leaks are invisible and generally
do not cause damage or injury. This
problem can also be summed up as ‘Over
Promise’ and ‘Lack of Delivery’. In the 1990s,
the basic compressed air inefficiency energy
transfer became a prime target for energy
reduction programs promising great results
with low investments. Good payback
programs – which they are if performed
correctly.

The least complicated part of any energy
reduction program, easiest to understand
and implement was to fix the leaks. ‘A single
6mm leak when fixed can give at least
£1400/year savings’ became the byword.

Management was easily persuaded to
support these low cost, high return
programs, but, in too many cases, the results
were ‘underwhelming’:
Some ‘professional leak specialists’ were
known to find more leaks than the actual air
supply.

Promised savings of thousands of
pounds worth of air (energy) reductions
failed to register even a small blip on the
customer’s monthly electric bill.

It didn’t take long for this situation to
often sour management on programs that
require financial and manpower investments.

Management might ‘talk the talk’ but
hesitated to ‘walk the walk’. That is not to
say that it was all bad, there were many
successful programs; however, we see the
same issues today with poorly implemented
programs continuing to disappoint the
customer.

Don’t overestimate size or
magnitude of leaks
In the past, most compressed air leaks were
sized with an educated estimate by
experienced professionals. When a
significant number of leaks were identified
and repaired, and if the situation allowed, the
total leak accuracy was checked with before
and after system actions such as flow meter
readings in off times, bleed down tests, etc.

The British Compressed Air Society
Installation Guide states:
When installing a new system the user
should agree with the installer the maximum
permissible leakage from the piping system
when it is subjected to a final leakage test
and before connection to the compressors
and airline equipment
When attempting to reduce leakage with
an existing system it should be recognised
that there is a point at which the cost of
locating and fixing the remaining leaks can
no longer be justified by the very small
amount of energy that would be saved. For
an installation with regular inspection and
maintenance, leakage should not exceed 5%
The major issue is that inexperienced
personnel often tend to overestimate the
actual volume (litres/second) which, when
the project is completed and the results are
disappointing, management support is lost.

Global leak load tests
In addition to measuring leak loads from the
bottom-up by listing individual leak sizes, it
can be useful to measure the overall system
leak load. During periods when the plant is
not in production, one can measure the total
leak volume with a monitored compressor
operation or a bleed down test as shown in
the BCAS Installation Guide:
This method requires a compressor of a
known capacity and an accurate pressure
gauge, Class 1 and not less than 100mm in
diameter, which has been recently calibrated
against a test gauge and a stopwatch or
timer.

Run the compressor with all equipment
isolated until the system is charged to
operating pressure and has remained at a
constant pressure for 1 minute: note the
pressure, P1, and time and stop the
compressor.

Due to air leaks the pressure will fall in
the system and should be allowed to drop to
some suitable point, P2, on the pressure
gauge scale not exceeding 1bar below the
maximum recorded reading. Note the time
in seconds for the pressure to fall to P2 and
restart the compressor. Record the time T
for the compressor to reach the maximum
pressure P1 and immediately it reaches the
previously recorded figure stop the
compressor.

Repeat this cycle at least four times to
obtain average values for T and t. If the
compressor capacity is Q L/s then the
amount of air delivered is Q x TL. Total
leakage time, however, is (T + t) seconds so
the average leakage rate is: (QxT)/(T+t)
litres per second.

Other Pressure and Leak testing methods
are given in the BCAS Installation Guide
and in the Pressure and Leak Test Guide.

Leak repair log
As leaks are identified and tagged for
subsequent repair, they should be tabulated
in a log sheet. Ideally this log would include
an estimate of the repair time, include
columns noting the actual repair date and
costs, and document who did the work.

This repair information will be very useful
when determining the true value of the leak
project.

Valuing the leak
After accurately identifying the magnitude
of the total leak list and repairing them, the
next significant challenge is to value the
effect of the leak project on the monthly or
annual electric bill. To management this is
where ‘the rubber meets the road’ – are
compressed air leaks worth fixing?
In the May/June issue of Industrial Plant &
Equipment I will show you how to calculate
compressed air leaks. You can then decide if
yours are worth fixing.