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How to Troubleshoot Purge & Pressurization Equipment

How to Troubleshoot Purge & Pressurization Equipment

1. Air leaks: The most common problem

Purge & Pressurization systems work  if your inlet supplies more air than air lost through leaks.  If your air supply is too low:

  1. The inert gas or air pressure inside your enclosure is too low to exclude hazardous gas or dust;
  2. The purge process cannot purge hazardous gas or dust from the enclosure;
  3. You cannot safely operate electrical equipment or motors;
  4. The purge unit stops you or the control system firing-up anything electrical.

We appreciate some readers may be frustrated. Your plant is down. It’s possible your purge system is doing its job and preventing explosions.

For all systems check:

  1. The inlet compressed-air pressure should be between 60 to 115 PSI, 4 to 8 bar. The compressed-air inlet pipe should be at least 3/8″ or 10mm Internal Diameter to ensure sufficient flow. Minimize bends for a smooth air-flow.
  2. No preventable air leaks from the enclosure or housing. e.g. unfilled conduit seals, unused holes etc….;
  3. The enclosure remains properly sealed.  Seals should stop water and dust entering the cabinet or enclosure.  Normally, seals allow a little pressurized air to escape.  However, if the inlet compressed air pressure is/was too high, the pressure bows out the enclosure’s door and sides. This breaks the seal so pressurized air leaks.

2. Continuous Flow system: Red=alarm green=pressurized indicator stays red


  1. An orifice plate fits to the Spark Arrestor Unit (SAU).  Without an orifice plate, the system may push too much air through the Spark Arrestor Unit. If so, the system cannot generate sufficient back-pressure. We provided a choice of seven orifice plates. Use one. The plate determines:
    • The purging time;
    • The volume of air or inert gas to generate 2.5 mbar, 1″ of Water Gauge, positive pressure;
    • The user manual describes which orifice plate to use, given your enclosure size and desired purge time.
  2. The Continuous Flow valve is open. Note: Clockwise closes the valve.

3. Leakage Compensation system: Red=alarm green=pressurized indicator stays red


  1. The Leakage Compensation valve is sufficiently open to compensate for leakage. NB: Leakage Compensation units compensate for up to 2 SCFM, 56 litres/minute leakage.

4. Black / yellow purging indicator does not change state.


  1. The relief valve (vent) connects to the flow sensor on the control unit. We recommend a minimum 1/8″, 4mm, Internal Diameter tube.

4. My leakage compensation (XLC) system completes a purge cycle. It moves into leakage compensation mode for a few seconds. Then the pressure indicator turns off, and the system starts a new purge cycle.

Insufficient Leakage Compensation air-flow. A component or enclosure seal probably failed.  Now, there’s  a new leak from your enclosure.

  1. Adjust the Leakage Compensation flow-valve counter-clockwise. This increases the air-flow in leakage compensation mode.

5. My gauge, inside my control unit, starts at 30 PSI. It then gradually or quickly falls to zero. Or, it doesn’t show a reading.

This gauge shows the pneumatic-logic supply-pressure. If this pressure is zero either:

Compressed air leaks from the regulator feeding air to the manifold. So

  • Feel for air leaking from displaced pipes, broken components, leaking gaskets, etc and fix.

Or, the control unit is damaged, because the

  • Air supply was contaminated (e.g. oil, water, dirt);
  • Control-unit was over-pressurized.

In which case replace the regulator.  Call Expo for part-number and pricing.