Expo Technologies Limited
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Page 5 of 7
ML384 Issue 03
–
09.01.13
2.3.2 Adjust the Leakage Compensation Valve (LCV) so
that the enclosure pressure rises to the point where the
“Pressurized” indicator turns green.
2.3.3 Continue to raise the PE pressure 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.
2.3.4 Lower the PE press
ure until the “Pressuized”
indicator turns Red. Check that the indicator turns Red at
or above the pressure specified in the documentation.
Check the external alarm contacts (if fitted).
2.3.5 Open the LCV again and set the PE pressure to a
level around 50% of the RLV operating pressures. This
“working” pressure is not critical. The “Pressurized”
indicator should be Green.
2.3.6
Turn the Purge Control Valve “On”. This will start the
High Purge Flow and the “Purging” indicator should turn
Yellow. If the “Purging” indicator remains Black the flow
through the outlet 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.
(Super-Mini-Purge
£
systems have a built-in gauge on the
filter for this purpose.) If the supply pressure is correct and
the “Purging” indicator does not turn Yellow, there is too
much leakage from the Pressurized Enclosure. Find and fix
the leaks!
“Purging” does not start until the indicator turns
Yellow
2.3.7
On LC and CFHP “Z” Purge systems the purge
timing function is performed by the user. When the
“Purging” indicator turns Yellow the Purge Flow is above
the minimum required and the purge time can start. The
user must ensure 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 as
shown on the PE or Expo system nameplate.
Never turn on the power without purging first unless
you have proved that the interior of the PE is gas free
and checked that the “Pressurized” indicator is green
!
2.3.8 After the purge time is completed the Purging Valve
should be turned “Off”. The High Purge Flow will cease
and the air flow into the enclosure will then be controlled
once again by the Leakage Compensation Valve (LCV), it
should now be re-adjusted if necessary. The RLV should
be closed and the enclosure pressure around 50% of the
RLV opening pressure. If this is not so there are three
possible situations:
a) Air continues to come out through the Spark Arrestor,
after High Purge has been turned “Off”, 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 the excessive opening 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 will start to open intermittently as the
PE pressure rises to the point where it exceeds the
RLV opening pressure. When the RLV opens the
pressure will fall quickly 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 re-closes and
the enclosure pressure starts to rise again. This is
entirely normal for this type of RLV and shows that it is
working correctly.
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 may be
around 2”WC (5 mbar) and will be the “normal working
pressure”.
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 LCV should be opened until the PE
pressure is around the normal working pressure.
2.3.9 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.
2.3.10
“Y” and “Z” purge systems do not control the
enclosure power. It is the responsibility of the user to
switch off the power whenever the enclosure pressure
falls below the minimum permitted i.e. when the
“Pressurized” indicator turns Red.
2.4 Normal
Operation
2.4.1
“X” Purge systems: Turn the air supply valve On
or Off to start or stop the system, After this the
Pressurizing and Purging sequence is entirely
automatic.
2.4.2
“Y” and “Z” Purge systems are started and
stopped in the same way as “X” purge system but the
user must close the Power Switch only after the
enclosure has been pressurized and purged sufficiently
to ensure that the interior of the enclosure is gas free. It
is the user’s responsibility to shut off the power, as soon
as possible after a pressure failure.
