Expo Technologies Limited
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Page 2 of 7
ML384 Issue 03
–
09.01.13
- For low flow rates, the Outlet Orifice may be incorporated
within the Relief Valve making use of the existing Spark
Arrestor. The Relief Valve will then have a suffix /CF**,
where ** is the orifice size in millimeters.
Section 1
Installation of the System
The installation of the MiniPurge
£
system, the
protective gas supply, any alarm device should be in
accordance with the requirements of NFPA 496.
The electrical installation associated with the
MiniPurge
£
system shall conform to the local codes
and the relevant clauses of NFPA 496.
1.1
Installation of the Expo LC and CFHP Systems
1.1.1 The Expo system should be installed either directly
on or as close as possible to the Pressurized Enclosure
(PE). It should be installed so that the system indicators
may be readily observed.
1.1.2 All parts of any system carry a common serial
number. If installing more than one system, ensure that
this commonality is maintained on each installation.
1.1.3 Any tubing, conduit and fittings used to connect to
the PE should be metallic, or, if non-metallic, conform to
the local codes for flammability ratings. No valve may be
fitted in any tube connecting the Expo system to the PE.
1.1.4 The user or manufacturer of the PE shall determine
the volume of the PE, the necessary purging volume, and
the time to be allowed for purging, using the chosen Expo
system purging flow rate. It is the user's responsibility to
verify or enter this data on the PE and/or Expo system
nameplate. Ask Expo if in doubt.
Example calculations:
a) If the PE external dimensions give a volume of 20 cubic
feet, and it is NOT a motor, multiply the volume by four to
get the Purging Volume i.e. 80 cubic feet. Divide the
Purging Volume by the purge rate e.g. 32 cubic feet per
minute, and round up to the next even minute above, i.e.
Purging time would be 4 minutes.
b) If the PE is a motor, multiply the internal free volume by
ten to get the Purging Volume. For the example above,
Purging time would be 8 minutes.
1.1.5 If the PE contains an internal source of release of
flammable gas or vapor, the procedures for assessment of
the release as given in NFPA 496 shall be observed. The
user must verify that the specification of the Expo system
e.g. pressures, continuous flow (dilution) rate and type of
protective gas are correct for the specific application. If an
inert protective gas is required, the Expo Control Unit can
be specified to have Compressed Air for the control logic
and Inert Gas for the protective gas to minimize Inert Gas
consumption.
1.1.6 More than one PE can be protected by a single
system. If PEs are connected and purged in “series” e.g.
“Daisy Chained”, the Outlet Orifice must be fitted on the
last enclosure with the Purge Inlet to the first enclosure.
The bore and length of the tube or conduit used to
interconnect the enclosures is critical and will determine
the maximum pressure experienced by the first enclosure
in the series. Advice on sizing can be obtained from Expo
Technologies. The test pressure for all the enclosures
should be 3 times the pressure inside the first
enclosure when purging is taking place.
If PE’s are to be connected in parallel each enclosure
must have its own outlet Relief Valve, Purge Flow
Sensor and Pressure Sensor. System “Models” can be
mixed e.g. Model LC for one enclosure and Model CF
for another. An example would be a Gas
Chromatograph instrument. Expo systems with this
facility have option code “TW”.
1.2 Quality
and
Installation
of the Pressurizing
Air or Inert Gas Supply
1.2.1 The source of the compressed air must be in a
non-classified area. Inert gas may be used as an
alternative to compressed air.
1.2.2 Unless a supply shut-off valve has been
specially fitted within the Expo system, a valve with the
same, or larger, thread size as the Control Unit inlet
fitting shall be fitted externally. In addition, for "Y" and
"Z" Pressurization systems, a suitable indicator shall
be provided.
1.2.3 The tubing and fittings used must conform to
1.1.3 above.
1.3
Provision and Installation of Alarm Devices
Expo Technologies systems have a Minimum Pressure
Sensor set to a pressure of at least 0.1” WC (0.25
mbar). When the PE pressure is above this set point
the Sensor produces a positive "Pressurized" signal.
This is displayed on a Red/Green indicator. This signal
can be used to operate an electrical contact for a
remote “Alarm”. The pneumatic signal may be supplied
either
a) to a pressure operated switch (MiniPurge
£
Option
Code /IS) suitable for an Intrinsically Safe circuit, in
accordance with Expo drawing EP80-2-11, (or for a
Non-Incendive circuit in Division 2), or
b) to a bulkhead fitting where it is available to the user
(MiniPurge
£
Option Code /PO). This signal can be
used to operate an external electrical switch either
local (e.g. explosionproof) or remote in a non-classified
area.
When the enclosure pressure falls below the set point
of the Sensor the "Pressurized" signal is removed, i.e.
the absence of the signal indicates
a “Alarm”
("Pressure Failure") condition. The user must make
use of this external alarm facility in accordance with
NFPA 496 requirements, if the system “Alarm”
indicator is not located in a place where it can be
readily observed.
Example: The "Pressurized" signal can be used to
produce an "Alarm" action by means of a conventional
"pressure switch" set to operate at around 15 psi (1
