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Commonly Requested Purge & Pressurization Options
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Commonly Requested Purge & Pressurization Options


1.What mounting options are available?

Panel Mount: The pneumatic regulators and valves sit inside the pressurized enclosure. The unit requires an external sensor to measure local atmospheric pressure.

Remote Purge System: You can locate the purge system away from the enclosure, although the distance should not be too great. We would be delighted to advise.

Relief Valve: This is normally sited diagonally opposite the purge air inlet. Alternative positions are possible, if the purge air flow thoroughly circulates through the enclosure. Complex enclosures may require a purge test to prove the purge system is effective.

SmartPurge II: Here the Relief Valve is part of the main enclosure. The intrinsically- safe purge air inlet valve is located separately.

2. What is the largest pressurized enclosure size?

Our IECEx/ATEX certification enables us to deliver certified enclosures up to 3370 litres – 2100mm x 1800mm x 1000mm.

The enclosure size can be much larger. We sometimes ship enclosures in sections, for on-site assembly. However, the air-flow rate and distribution requires skilled design. Large complex enclosures may require a purge test that proves the purging is effective.

3. What output switches are available?

Expo’s expertise supports all electrical requirements and local variations. Common customer requests include:

/PO option: Brings system-generated pneumatic signals to 1/8″ NPT bulkhead fittings, so you can pipe the signal onward.

/IS option: has an internal switch or switches.

/IS Z-purge option: These units are for Division 2/Zone 2 installation. The /IS option delivers an encapsulated internal switch:

  • Labelled as Ex m (ATEX, Manufacturers Declaration) and hermetically sealed (US);
  • Connect to an intrinsically-safe, non-incendive, OR other protected circuit;
  • 2m flying leads to meet local standards;
  • Expo Drawing EP80-2-11 provides wiring guidance.

/PA Option: satisfies IEC/ATEX applications in Zone 1. Expo provides:

  • IEC/ATEX certified components;
  • Ex de pressure switches wired to Ex e terminals in an Ex e junction box, ready assembled onto the purge system housing.

Explosion-Proof Junction Boxes: for Zone 1/Division 1, and connected to appropriate internal pressure switches. The Expo MIU datasheet describes common variations.

SmartPurge II is a self contained system:

  • Approved under IECEx/ATEX;
  • Incorporates power interfacing relays & terminals within the (Ex e) product enclosure ;
  • Includes power-Interlock terminals – up to 250Vac/6A or 28VDC/5A;
  • Separate volt-free system status contacts suitable for inclusion in an intrinsically safe circuit;
  • SmartPurge II manual contains  full details.

4. Should push-buttons, lamps, switches, and keyboards on the pressurized enclosure be Ex rated ?

Our enclosures can contain any equipment want.However, to comply with our certification, everything that protrudes through the enclosure’s wall, or is outside the wall and powered must either:

  • Be already certified. For  IECEx enclosure certificates, that equipment must be IECEx-approved;
  • Complies with the general requirements of hazardous areas standards. This mainly concerns impact resistance and temperature rise.

Nevertheless, our pressurized enclosure certificate enables us to use a wide range of appropriate components. Often, we evaluate alternatives or specific components for customers.

Usually we mount instruments and complex equipment on a sub-assembly, behind a viewing window. Please note that the higher internal pressure can effect flexible components such as membrane keyboards and display screens.