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Purged Enclosure is used for housing Normal Electrical equipment in an extremely hazardous & explosive environment.
The basic on which Purge Panels are designed is “ Fluid always flows from higher pressure to lower pressure.” It is the process of supplying an enclosure with clean air or an inert gas at sufficient flow & positive pressure to reduce to an acceptably safe level the concentration of flammable gases or vapours initially present, and to maintain this safe level by positive pressure with or without continuous flow.
 
Purge Panel
PRESSURIZATION WITH LEAKAGE COMPENSATION


The operation of pressurized equipment can be divided into 3 phases:
A) FLUSHING PHASE
B) OPERATIONAL PHASE
C) PRESSURE FAILURE CONDITION


The first phase starts with energizing the control unit, an inert gas (usually clean air) flows through an Air Filter Regulator (AFR) in the enclosure to be purged to expel any potentially explosive gas / air mixture. The quantity of air required for purging must be at least 4 times the volume of the free space in the enclosure (as per NFPA - 496). The time for purging is calculated based on flow rate and volume of enclosure. The control circuitry is designed based on the above calculation. In the operational phase, a positive pressure is maintained in the enclosure, which prevents dangerous gases or vapors from entering in it & coming into contact with the arching electrical components, the installation after this can now be operated without any danger.
A by-pass solenoid valve will compensate pressure loss. In case of a pressure failure phase, should the pressure of the enclosure fall below the value preset at the pressure regulator then installation will signal the alarm and/or trip depending on the user (we take the preset value of lower pressure as 6 mm of water column, as per NFPA- 496)

Enclosure for electrical equipment in hazardous locations is made safe by one of the three methods :

Purged enclosure for housing with normal electrical equipment.
Explosion proof enclosure for housing with normal electrical equipment.
Normal enclosure for housing with explosion proof electrical equipment.
PURGING DETAILS
Hazadous Area Classification
Commonly used RGUFES Continuous hazards more than 1000 hrs./annum Intermediate Hazards
Between 10 & 1000 hrs./annum		 Hazardous under abnormal conditions between 0.1 & hrs./annum
IES/CENEL/Europe ZDNE 0(Gases, ZONE Z (10)(Dust) ZDNE 1(Gases, ZONE Z (10)(Dust) ZDNE 2(Gases, ZONE Y (10)(Dust)
North America DMISION1 (Gases & Dust)  DMISION1(Gases & Dust) 

Purging Sequence
 
System Start-up
  
Pressurized Enclosure
door Closed
 
Pressurised air On :
Power On
 
Starting of purging
Flushing for set time
 
 
Closure for vent & air
ontrol valve opens
 
Possitive pressure is
maintained in enclosure
 
pr. drops below set value
pr. switch is activeted
 
Pressure Failure
 
Pressurising air supply
turn off.
Closure door opened
or excessive leakage.
Exclosure pressure falls
below the minimum.
Alarm & Trip
(X- type purge)
Alarm Only
(Y & Z type purge).
Technique
Mathod of
Protection
Segregation
Ol mmertion
Pressurization
powder filling
Encapsulation
Redifined
Machenical
Design
Encreased Safety
Non- Encendive
Energy
Limiting
Intrinsic Safety
Containment
Flame Proof
Products
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