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How to Design Expo Equipment into a hazardous area
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How to Design Expo Equipment into a hazardous area


1. What air quality is required?

Clean, dry and uncontaminated air at 4 bar (60 psi) minimum supply pressure. Dirty, damp air may shorten the life of the electrical equipment.

2. Can the customer install equipment inside the enclosure?

Yes. You can install equipment inside an Expo pressurized enclosure. Expo provides clear guidelines.

Ensuring the air-flow purges a large, complex enclosure requires considerable expertise. Complex enclosures often require a purge test to prove the purging is effective. We provide assistance. However, if Expo certifies your enclosure, then Expo must inspect your enclosure.

3. Can fan air purge enclosures?

Yes. Different hardware is required, although the purge system operates the same way. Customers request fan systems if:

  • Compressed air is unavailable;
  • The pressurized enclosure requires more compressed air than the on-site can supply.

4. What about heat dissipation?

Internally-generated heat can dissipate through the pressurized enclosure walls or through attached heat sinks. If your equipment doesn’t achieve your desired T-rating, Expo provides a range of sophisticated heat management systems.

5. Can the Continuous (air)Flow system cool electronic equipment?

The Continuous Flow purge system is designed to prevent explosions, not to cool equipment. We make no claims nor offer guarantees the purge system will decrease temperatures inside the enclosure. Nevertheless, we:

  • Indicate what cooling effect might occur;
  • Often deliver properly engineered cabinet cooling solutions.

6. What power does the purge unit need?

The base purge unit is completely pneumatic. It requires a minimum of 4 barg/60 PSIG to operate.

The MiniPurge /ET version includes a self-contained intrinsically-safe timer module:

  • You can accurately set purge times between 1 and 99 minutes.
  • The Electronic Timer is IECEx/ATEX/FM approved.

The Electronic Timer’s battery:

  • Has a 10 year shelf life.
  • Is is designed to last 3 years, if used once/day for a 15 to 30 minute purge cycle.
  • N.B. International standards on the maintenance of hazardous area electrical equipment recommends all equipment is regularly serviced. The interval should not exceed 3 years.
  • Replace the battery in the field at any time without affecting the protected system.

The SmartPurge II acts like an intelligent Relief Valve. The SmartPurge II connects to an intrinsically-safe purge air inlet valve, and it measures the exhaust flow at the SmartPurge II. SmartPurge II Power Requirements: 90-254Vac or 11-28VDC.

7. What is the difference between X, Y & Z purge systems?

X-rated purge systems allow uncertified equipment to be installed in Zone 1 (Division 1). Usually, power to the enclosure is switched off if pressurization is lost.

Y-rated purge systems allow Zone 2 (Division 2) certified equipment to be installed in Zone 1 (Division 1). Usually an alarm sounds if pressurization is lost.

Z-rated purge system allow uncertified equipment to be installed in Zone 2 (Division 2). Usually, an alarm sounds if pressurization is lost.

8. When does electrical power need to be automatically disconnected?

X purge systems require internal power isolation on pressurization loss. Except:

  • If power disconnection may lead to a more dangerous situation;
  • Safety-critical systems, e.g. emergency shutdown, public address, general alarm system; which should remain powered when pressurization is lost.

Many users require automatic power disconnection in Zone 2 & Division 2, if they believe:

  • Safety is improved;
  • Local operator reaction to alarms signalling pressurization loss is likely to be delayed.

Series Purging

1. What size pipe should connect enclosures purged in series?

The pipe should be a minimum of 1″ ID (Internal Diameter) for a size1purge unit. The bigger the pipe ID, the better the air-flow.

2. Which enclosure is purged first?

Best practice is to purge in ascending order – from smallest to largest. Larger enclosures often leak greater volumes of compressed air. So, leakage from a large enclosure may starve a downstream small enclosure of compressed air.