Expo Technologies Limited
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Page 7 of 7
ML384 Issue 03
–
09.01.13
Possible cause 1:
Insufficient purging Flow due to
inadequate air supply pressure. Check the air supply
pressure at the inlet to the CU when flow is taking place.
Excessive pressure drop in the supply pipe is a very
common cause of this problem. The supply pipe must be at
least as big as the CU inlet fitting, i.
e. at least ½” NB (12
mm). Super-MiniPurge
£
systems with ¾” or 1” connections
must have AT LEAST this internal diameter for supply and
outlet tubing. Due to the high flows demanded from these
large systems the need for adequate supply tubing is
VITAL. If in doubt, or for long distances, install tubing that
is at least 50% larger than the inlet size!
Possible cause 2: Excessive Pressurized Enclosure (PE)
leakage. Check around the PE when flow is taking place.
Any significant leakage must be cured. Has a Leakage
Test been done? The total leakage should not exceed 10%
of the Purge Flow Sensor setting. Check for leakage down
the conduit through unsealed stopping boxes.
Possible cause 3: PE not strong enough. Repeat the PE
pressure test. Is is recommended that the PE is tested to
three times the Relief Valve opening pressure e.g. 12”WC
(30 mbar) for systems with default settings. Has this been
done?
Possible cause 4: The tubing from the RLV Flow Sensing
point to the Purge Flow Sensor is not air-tight e.g. fitting
nuts not tightened or tube damaged. Check and repair as
necessary.
Possible cause 5: The Purge Flow Sensor is not operating
correctly or out of calibration. The basic operation of the
Purge Flow Sensor can be checked by unscrewing the 2.4”
(60 mm) diameter diaphragm and by using a finger, block
the threaded hole in the top of the valve module. The valve
should operate and the indicator turn Yellow. If this works
correctly and the flow through the Relief Valve is above the
minimum required WITH THE RELIEF VALVE COVER
FIRMLY SECURED IN PLACE the Sensor diaphragm
needs re-calibrating or replacing.
4.5 System
Fails
to
Switch
Power On after the Purge
Time has Elapsed? (“X”
-Purge Systems Only)
Possible cause 1: Is power available? Is the power
disconnect closed? Are the fuses or circuit breaker OK?
Possible cause 2: System fault? Timer not timed out?
a)
Has the “Purging” indicator been Yellow for the whole of
the purge time?
b) Is the logic pressure gauge at 30 psi (2 bar)
r
10%.
c) Is there pressure at the Power Switch output bulkhead
and at the Power Switch itself? Is the Switch set at 15 psi
(1 bar)?
d) Is the pipe to the Power Switch airtight? The signal
to the Power Switch bulkhead has a restrictor that
limits the permissible leakage from the pipe.
e) Note the timer setting. Reset the timer to the
minimum available purging period (see 2.2.6) and
check operation on that purge time. If it works OK,
increase the time progressively until either it is correct,
or the system ceases to time out at all. In the latter
case, there is an air leak in the timer circuit. (A leak in
the timing circuit can cause the timer not to time out.) If
possible, establish the source of the leak with soapy
water and retest the system. This will involve removing
the chassis from the Control Unit
–
be sure this is the
cause before starting the work. It is VERY unusual!!
Ensure that the timer is returned to its original
setting and the purge time checked before putting
the system back into service.
Possible cause 3: Power Switch Fault. Check the
operation of the Power Switch. It should close above 20 psi
(1.4 bar).
4.6
Pressure Sensor Calibration
If it is decided that the Minimum Pressure Sensor or
Purge Flow Sensor needs re-calibrating it can either be
returned to Expo for this service or it can be done by
the user as follows:
Disconnect the pressure sensing pipe from the top of
the diaphragm. (It is a “push
-
in” quick release fitting;
firmly push inwards the collar surrounding the pipe
where it enters the fitting, and then pull the pipe
outwards while maintaining the pressure on the collar).
Unscrew the 2.4” (60 mm) diameter diaphragm
housing from the top of the Sensor. Invert it and note
the brass adjusting screw in the center. Turning the
screw inwards (clockwise) will lower the setting. It is
likely that the screw will be very stiff due to the locking
sealant. If the screw cannot be moved the application
of gentle heat in the area of the brass screw can often
help. DO NOT OVERHEAT!
4.7 Filter
Cleaning
If the filter element needs cleaning the transparent
bowl can be unscrewed and removed. The filter
element also unscrews and can then be cleaned in
soapy water. Do not use solvents on any part of the
filter assembly.
Expo Technologies tip: It is sometime easier, if the bowl
is very tight, to remove the filter by undoing the fitting
that holds the filter into the Control Unit. On Sub-Mini-X-
Purge
£
systems it may be necessary to remove the
Minimum Pressure Sensor diaphragm first.
Section 5
Annex of Options fitted
Refer to the annex of this manual for any options fitted as designated by the model code of the system
Expo
Technologies
Ltd Expo
Technologies
Inc,
Unit
2
The
Summit, 9140
Ravenna
Road
Unit
#3,
Hanworth
Road,
Twinsburg,
Sunbury-On-Thames,
OH 44087,
TW16 5DB. UK.
U.S.A.
