Expo Technologies Limited
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Page 4 of 7
ML384 Issue 03
–
09.01.13
On LC and CFHP "X" Purge systems proceed as follows:
2.2.1 Open the Leakage Compensation Valve (LCV) to
about 50% of its travel.
2.2.2 Open the supply shutoff valve SLOWLY and allow
the PE pressure to rise until the Relief Valve (RLV) opens.
Check that the RLV opens at or below the figure specified
in the documentation. Repeat the test several times.
2.2.3 Open the supply shutoff valve fully and the purging
flow will start.
2.2.4 Check that the internal logic gauge reads 30 psi (2
bar). If not, adjust the logic pressure regulator to suit (lift
the red ring to unlock the knob first.)
2.2.5
At this time the “Pressurized” indicator should be
Green and the “Purging” indicator should be Yellow. If the
"Purging" indicator remains Black the flow through the
Relief Valve is below the minimum for which the Flow
Sensor has been calibrated. Check the air supply pressure
at the inlet to the Control Unit while purging is taking
place
. It must be above the minimum specified. The larger
Super-Mini-X-Purge
£
system has a built-in gauge on the
filter for this purpose.
2.2.6 On LC and CFHP "X" purge systems the purge timer
will start as soon as the “Purging” indicator turns Yellow.
Check that the time delay between the indicator turning
Yellow and the application of power to the PE is not less
than the minimum time required to purge the PE. Times in
excess of the minimum are permitted and a tolerance of
+25% is normally acceptable. If the time is too short it must
be adjusted accordingly.
The system uses a pneumatic incremental timer which is
adjusted by fully opening or closing one or more of five
screwdriver-operated valves, arranged in a block on the
control logic manifold
–
see GA Drawing. The opening of
each valve incrementally provides a fixed number of
minutes of purging time as in the following table
Valve:
1
2
3
4
5
Minutes:
2
4
8
8
16
Thus for a 12-minute purge time, valves 2 and 3 would be
open and the others closed. For twenty-four minutes, 4 and
5 would be open and the others closed.
At least one valve
must always be open and the screws must be at the
appropriate limit of travel
.
2.2.7 After the power has been turned on by the Control
Unit, the Purging Valve will close and the air flow into the
enclosure will be controlled by the Leakage Compensation
Valve (LCV). The initial setting of 50% open may be too
high or too low. It should now be adjusted to set the PE
pressure and leakage.
There are three possible situations:
a) Air continues to come out through the RLV Spark
Arrestor after power has been turned on in considerable
quantity. The LCV is too far open and the air flow is holding
the RLV open continuously. (Note: Some CFHP systems
have a deliberate but modest “Continuous” air flow through
the RLV in normal operation; do not confuse this flow rate
with that caused by excessive setting of the LCV.) Close
the LCV slowly observing the manometer or gauge (see
item 2.1.3 above). The PE pressure will start to fall as the
flow decreases but eventually the RLV will close and
the pressure rise again. At this point the Relief Valve
may start to open intermittently as the PE pressure
rises to the point where the RLV re-closes and the
enclosure pressure starts to rise again. This is entirely
normal for this type of RLV. Proceed now to b) below:
b) If the Relief Valve is opening intermittently the LCV
is slightly too far open. Observe the manometer or
gauge. When the RLV opens the enclosure pressure
falls quickly to the point where the RLV recloses and
the enclosure pressure starts to rise again. This is
entirely normal for this type of RLV and shows that it is
working correctly.
Then continue to close the LCV until the cycling stops
and the enclosure pressure starts to fall. Carefully
adjust the LCV until the PE pressure is approximately
50% of the RLV opening pressure and stable. This
pressure ma
y be around 2” WC (5 mbar) and will be
the “normal working pressure”.
We recommend that the setting of the Minimum
Pressure Sensor is checked at this time. Note the
position of the LCV knob. Slowly lower the PE
pressure by closing the LCV further counting the
number of turns from the “normal working pressure”
position. Note the pressure at which the “Pressurized”
indicator turns Red and check that it is not lower than
the figure given in the documentation. Check also the
“Alarm” electrical contacts (if fitt
ed).
As soon as the “Pressurized” indicator turns Red, the
enclosure power will be switched off (see also 2.2.8
below) and the system will start to re-purge.
While it is re-
purging return the LCV to its “Normal
Working Pressure” position so that, at the en
d of
purging the enclosure pressure should immediately
settle down at the correct “normal” pressure. Finally re
-
adjust the LCV if necessary.
c) If, at the end of purging, the PE pressure falls below
the Minimum Pressure Sensor setting the LCV is not
open far enough. The system will start to purge again.
While it is purging open the LCV fully and check the
enclosure for leakage. This time, at the end of purging,
the enclosure should stay pressurized and the Relief
Valve action be as in a) or b) above. It is likely that
there is significant leakage from the enclosure and
attempts to reduce the leakage will be time well spent.
CFHP systems are intended to have a Continuous
Flow through the enclosure. The Continuous Flow may
emerge through the RLV, in which case the RLV will
have a “CF” in its model number. Some CFHP systems
will have a separate Outlet Orifice/Spark Arrestor and
air can be felt emerging through this aperture
whenever the enclosure is pressurized.
2.3 Commissioning
Leakage Compensation (LC)
and
Continuous Flow/High Purge (CFHP) “Y” and
“Z” Systems.
On LC and CFHP “Y” and “Z” Purge systems, proceed
as follows:
2.3.1 Open the supply shutoff valve.
