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- Has the PE door been closed and all conduit/cable glands
sealed?
- Is the PE leaking too much?
Possible cause 3: Air supply fault?
Insufficient purge Flow due to inadequate air supply
pressure/flow. Check the air supply pressure at the inlet to
the CU when flow is taking place. Excessive pressure drop
in the supply pipe is 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.
Possible cause 4: Excessive PE Leakage?
Check around the PE when flow is taking place. Any
significant leakage must be cured. Has a Leakage Test been
completed? The total leakage should not exceed 10% of the
Continues Flow rate.
Possible cause 5: PE not strong enough?
Repeat the PE Pressure Test. FM recommend that the PE
is tested to three times the Relief Valve opening pressure
e.g. 12"wc (30 mbarg) for standard units. Has this test been
done?
Possible cause 6: Unit fault?
Has the pressure sensor tube been damaged?
If checks above reveal that the PE is correct, the fault
probably lies in the Control Unit. The basic operation of the
Minimum Pressure Sensor can be checked by unscrewing
the 2.4" (60mm) 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 should turn Green. If
this works correctly and the enclosure pressure is above the
setting of the Minimum Pressure Sensor it is likely that the
Pressure Sensor diaphragm needs re-calibrating or
replacing. (See 4.6)
4.3 Relief Valve Opens (Continuously or Intermittently)
Possible cause 1: The PE pressure is too high. The Flow
Control Valve (FCV) is too far open. Adjust the FCV as
described in Section 2 above.
Possible cause 2: Debris on the RLV disk allowing air to
leak from the valve. Remove the RLV cover and clean the
valve disk. The disk and spring may be removed from the
RLV without affecting the calibration.
4.4 "Purging" Indicator Will Not Turn Green During
Purging
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).
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. It is recommended that the PE is tested to
three times the Relief Valve opening pressure e.g. 12"WC
(30 mbar) for units with default settings.
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 Pressure Sensor Calibration
If it is decided that the Minimum Pressure Sensor
Flow Sensor needs re-calibrating it can either be returned to
Hoffman 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!
4.6 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.
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.
/
Purge
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