EXPO MiniPurge D825/ET, Руководство пользователя, Страница: 26 / 40

Expo Technologies Limited
¤ ¤
Page 3 of 7 ML384 Issue 03 – 09.01.13
bar). The "Pressurized" signal from the CU at 30 psi (2 bar)
or more will hold the switch in the operated position until
the CU detects a low pressure in the PE and removes the
"Pressurized" signal. The Alarm switch will reset and its
contacts can be used to operate a remote electrical alarm.
If the switch is located in the hazardous area it must either
be part of an Intrinsically Safe circuit, or be suitably
protected e.g. explosionproof. The pressure switch should
be IS or explosionproof even if it is fitted within the
Pressurized Enclosure.
Expo Technologies Tip : Exception: For a “Z Purge”
system fitted in a Division 2 area, a non-classified
switch inside the PE can be used to operate a remote
Alarm provided its electrical supply comes from within
the PE (i.e. NOT PROVIDING DRY CONTACTS). When
the PE is in use the Alarm can operate normally in
response to the pneumatic signal from the CU with
option /PO. When the PE power is switched off there is
no need for an alarm! Ask for the circuit diagram.
The Alarm switch can also be located in a nearby non-
classified location. To get the best response time the switch
should be as close as possible to the CU and the maximum
length of tubing between the CU and the Alarm switch should
not exceed 150 feet (45 m) unless “Quick Exhaust Valves”
are used (please ask Expo if in doubt).
Note: No valves may be fitted between the Expo system
and the alarm switch.
1.4 Power Supplies and their Isolation
1.4.1 All power entering the PE shall be provided with a
means of isolation. This requirement also applies to any
external power sources that are connected to "dry
contacts" or "volt-free contacts" within the PE.
Exception: Power to Intrinsically Safe, or other apparatus,
which is already suitable for the location, need not be
isolated by the Expo Technologies system.
Expo Technologies Tip: It is recommended to fit dry or
volt-free contacts in the non-classified area or inside
an explosionproof box rather than inside the PE.
Please ask Expo about “MiniPurge
£
Interface Units”
(MIU).
In the case of "X" Pressurization, the isolation of the power
must be controlled by the Expo system using the "Purge
Complete" pneumatic signal to operate a "Power Switch" in
a similar manner to that described in 1.3 above.
In the case of "Y" or "Z" Pressurization the power may be
controlled manually by the user by the use of local isolating
switch.
1.4.2 In accordance with NFPA 496 , Expo Mini-X-
Purge
£
systems can have the "Action on Pressure
Failure" (normally "Alarm and Trip") adjusted by the
user to become "Alarm Only". In case of an alarm, it is
the responsibility of the user to de-energize the
protected equipment as soon as possible. The system
may require the addition of an “Alarm Only Kit” (/AO) to
perform this function. Please contact Expo
Technologies Sales office for further details.
1.4.3 The Power (cut-off) Switch must be approved for
the location or located in a non-classified area.
1.4.4 No valves are permitted between the Power
Switch and the Expo system.
1.4.5 For "X" Pressurization, the PE door shall have
fasteners that can be opened only by the use of a tool
or key. Otherwise the additional requirements from
NFPA 496 should apply.
Note: The door switch provided with the Expo system
(when requested) can be either pneumatic or electric.
1.5 Marking
1.5.1 The MiniPurge
£
system carries a nameplate and
a specification sheet, which give specific data such as
serial and models numbers, Pressure Sensor settings,
flow rates and purge time.
1.5.2 Other marking, for the PE, required by the
standard includes:
“ WARNING - PRESSURIZED ENCLOSURE
This enclosure shall not be opened unless the
area is known to be free of flammable materials or
unless all devices within have been de-energized"
"Power shall not be restored after the enclosure
has been opened until the enclosure has been
purged for____minutes at a flow rate of_____."
Expo note: It is understood that NFPA 496 requires the
de-energization of all devices that are not suitable for
the hazard e.g. devices that are not Explosionproof or
Intrinsically Safe. For example, an explosionproof anti-
condensation heater would not have to be de-
energized.
1.5.3 If Inert Gas is used as the Protective Gas and a
risk of asphyxiation exists, a suitable warning plate
should be fitted to the PE.
Section 2 Operation of the System
2.1 Initial Commissioning
2.1.1 Check that the system has been installed in
accordance with Section 1 of this manual.
2.1.2 Disconnect the supply pipe from the inlet to the
Control Unit and blow clean air through for at least 5
seconds per foot of length (15 sec / metre) to remove any
debris, oil and condensation.
2.1.3 Connect a temporary pressure gauge or liquid
ma
nometer to the PE or Control Unit “Pressure Test
Point”, [on the LP Sensor, by the removal of the Red
plug - 5/32” (4mm) OD nylon tube].
2.2 Commissioning Leakage Compensation (LC)
and Continuous Flow High Purge (CFHP) ”X”
Purge systems.