Frequent Asked Questions

General

Purge and Pressurization

Series Purging

Troubleshooting

General

1. What’s the difference between Leakage Compensation and Continuous Flow Systems ?

a) The Continuous Flow system will continuously flow air through the control panel. The flow rate depends on which orifice plate you choose. Applications: small enclosures and analyzers.
b) The Leakage Compensation system purges the enclosure; and then shuts itself down and just tops off for any leakages your enclosure may have. It will maintain a minimum pressure in the enclosure.

2. How much money do you want to spend ?

- CF is more economical to purchase but continuous consumption of the purge medium
- LC is more expensive up front but the customer should recoup the costs in about a 6 month period in purge medium savings

3. What quality of air is required ?

Clean and uncontaminated air at 4 bar (60 psi) minimum supply pressure. You wouldn't like dirty and damp air blowing over your electronics, would you ?

4. Can we mount the purge system inside the PE, or away from the PE, on a nearby wall or framework ?

Because we have to measure internal pressure against atmosphere, mounting the purge system inside the PE would not allow external atmosphere to be measured. We could do this however by employing a panel mount system where ext. atmosphere can be measured.
Mounting the system nearby is ok as long as the distance is not too far. Pressure sensing accuracy is reduced when pipe work is too long or tortuous.

5. What is the size limit on EXPO's PE`s that can be offer ?

If full ATEX cert is required, we hold certification on an extremely variable range, up to 1701 liters volume. There is no realistic limit to construction, as PE`s can be built in sections, and reassembled. Air requirements to purge large enclosures does need to be carefully considered, so please ask.

6. Does Expo have to build the equipment inside a PE, or can we do the assembly ?

You can do the assembly yourself, and there are guidelines to follow, when doing so. We offer assistance here, and have to inspect before issuing the appropriate paperwork.

7. Do pushbuttons, lamps, switches, and keyboards have to be Ex rated ?

They have to comply with the hazardous area standards general requirements. We include a selection as part of our PE certificates. So not Ex rated, but selected. Controls we can cover, but most instrumentation needs to be on a sub assembly, mounted behind a viewing window in the PE wall.

8. What about heat dissipation?

A certain amount of heat can be dissipated through the PE enclosure walls, to maintain particular “T” ratings. When this can not be done satisfactorily, then cooling methods have to be employed. Expo offer a range of heat management systems.

9. Can fan air be used for purging ?

Yes. The purge system would still do the same controlling, but the hardware would be different. Fan systems are often employed when compressed air is not available or when large PE`s are used, and the compressed air system cannot cope with the volume of air needed.

Purge and Pressurization

1. Why should I use Purging over Explosion Proof as a method to protect my equipment ?

There are two philosophies that are applied here the first is that if an explosion occurs our box will contain it (explosion proof) and the second is that an explosion will not occur because there are no hazardous gases present to ignite the explosion (Purging). What needs to be evaluated is the cost of maintaining the products. If the box is constantly exploding the product inside the box will need to be replaced. With purging the product inside the box will have a longer shelf life because it is not under as much stress. In many cases the cost of purging a piece of electrical equipment will be as much as 50% less expensive up front and you will still have a lower maintenance cost as well.

2. What is the difference between Y & Z purge systems ?

The “Z & Y” purge systems are the same unit, with the letter designating the internal equipment worst case of area compliance. A Y-Purge unit allows a Div. 2 rated item to be safely installed in a Div 1 environment. A Z-Purge unit allows an unclassified piece of equipment to be mounted into a Div. 2 area.

3. Can I use the continuous airflow of a CF system to cool my electronics ?

We have never had our system tested to reflect cooling capabilities and we make no claim that the temperature in the enclosure will decrease. If cooling is an issue we recommend the purchase of our cabinet cooler.

4. Can I use the IS Switch on the system to switch power?

Because the IS switch is actuated by the control unit when pressure is ok rather than when purge is complete you cannot use this for switching power into your enclosure. The standard allows the using to monitor the purge time and once complete manually apply the power. The same applies to loss of pressure.

5. Can I use the IS Switch on the system with a general purpose circuit?

If you are using the panel mount style of system you may use this switch in a general purpose way as long as the power is not being applied to the enclosure until after purge is complete.

6. How do I hook up the power to the purge unit ?

The purge unit is completely pneumatic and only requires 60-115 PSI to run properly.

7. What do you mean by IS or non-incendive circuit ?

An IS circuit as defined in the NEC article 504 “A circuit in which any spark or thermal effect is incapable of causing ignition of a mixture of flammable or combustible material in air under prescribed test conditions.” This is accomplished with the use of a barrier that keeps the circuit low power. This type of circuit is allowed in Class I Division 1 and 2 areas. Non-incendive circuits are the same as the IS circuit except that a barrier is not required. The equipment that is being used is naturally low voltage and will not cause arcs or sparks. This form of protection is only acceptable in Class I Division 2 areas.

Series Purging

1. What size pipe should I have between the enclosures that are purged in series ?

The pipe should be a minimum of 1 ½” ID when using a size 1 purge unit. The bigger the ID of the pipe the better it is for creating the proper flow.

2. How do I choose which enclosure to purge first in series ?

When at all possible you should purge from the smallest enclosure to the largest. Air looks to find a space to go to next therefore by purging the smaller enclosure first you give the air the best opportunity to find the larger enclosure. The larger enclosure will have more of a chance for leakage and may cause the smaller enclosure to be starved of proper pressure or flow.

Troubleshooting

1. I cannot get the red alarm / green pressurized indicator to change colors.

a. Check to make sure that an orifice plate (one of eight included with the system) is positioned in the spark arrestor unit. Without an orifice plate the system could be passing too much air through the (SAU) Spark Arrestor Unit and positive pressure cannot be produced within the enclosure. The proper selection of an orifice plate will not only determine the time needed to purge the unit but also the amount of air or inert gas needed to generate the positive pressure of 1” of Water column (wc). Refer to our Choose Your Own NFPA booklet for proper selection of the orifice plate when compared to enclosure size and purge time desired.
b. Check to make sure the inlet pipe is at least a 3/8” I.D. bore. We recommend using minimum bends to insure smoother air flow.
c. Make sure that the continuous flow valve is open. Note: Clockwise closes the valve.
d. If all of the above have checked out inspect the enclosure for unnecessary leakage (i.e. unfilled conduit seals, unused holes etc….)
e. Make sure that enclosure is properly sealed. Note that NEMA 4 cabinets although they are designed to keep water and dust from entering the enclosure they have not been designed to keep pressure from escaping. Pressure naturally bows the door and sides of the enclosure thus creating leaks. Example: 5 ft³ enclosure has one latch at center of door.

2. My red alarm / green pressurized indicator will not change state.

a. Check to see if you have the proper air supply line I.D. coming to the controller. Z & Y need at least 3/8” I.D. bore in order to have proper flow volume.
b. Inspect the enclosure for unnecessary leakage (i.e. unfilled conduit seals, unused holes etc….)
c. Make sure that enclosure is properly sealed. Note that although NEMA 4 cabinets are designed to keep water and dust from entering the enclosure they have not been designed to keep pressure from escaping. Pressure naturally bows the door and sides of the enclosure thus creating leaks. Example: 5 ft³ enclosure has one latch at center of door.
d. Make sure that the leakage compensation valve is open far enough to compensate for leakage. Note: LC units will compensate for up to 2 SCFM of leakage.

3. My black / yellow purging indicator is not changing state.

a. Check to see if you have the proper air supply line I.D. coming to the controller. Z & Y need at least 3/8” I.D. bore in order to have proper flow volume.
b. Inspect the enclosure for unnecessary leakage (i.e. unfilled conduit seals, unused holes etc….)
c. Make sure that enclosure is properly sealed. Note that although NEMA 4 cabinets are designed to keep water and dust from entering the enclosure they have not been designed to keep pressure from escaping. Pressure naturally bows the door and sides of the enclosure thus creating leaks. Example: 5 ft³ enclosure has one latch at center of door.
d. Make sure that the relief valve (vent) is connected back to the flow sensor on the control unit. We recommend using a minimum 1/8” tube.

4. I can not get my red/green indicator to change state.

a. Check and make sure you have the proper air inlet pressure and size. Should be 3/8” ID pipe and 60-115 PSI.
b. If you are using a Continuous Flow (CF) unit check to make sure that an orifice plate (one of eight included with the system) is positioned in the Spark Arrestor Unit. Without an orifice plate the system could be passing too much air through so, the (SAU) Spark Arrestor Unit and positive pressure cannot be produced within the enclosure. The proper selection of an orifice plate will not only determine the time needed to purge the unit but also the amount of air or inert gas needed to generate the positive pressure of 1” of Water column (wc). Refer to our Choose Your Own NFPA booklet for proper selection of the orifice plate when compared to enclosure size and purge time desired.
c. Open the control unit door and make sure that the logic pressure gauge is holding steady between 25-35PSI or 1 ½ to 2 ½ bar. If this is the case the logics of the unit is running good and there may be three possible problems.

• Enclosure has too much leakage, check the door first
• The inlet pipe is too small or does not have enough pressure

5. I cannot get my black / yellow indicator to change state.

a. Check and make sure you have the proper air inlet pressure and size. Should be 3/8” ID pipe and 60-115 PSI.
b. If you are using a Continuous Flow (CF) unit check to make sure that an orifice plate (one of eight included with the system) is positioned in the Spark Arrestor Unit. Without an orifice plate the system could be passing too much air through the (SAU) Spark Arrestor Unit and positive pressure cannot be produced within the enclosure. The proper selection of an orifice plate will not only determine the time needed to purge the unit but also the amount of air or inert gas needed to generate the positive pressure of 1” of Water column (wc). Refer to our Choose Your Own NFPA booklet for proper selection of the orifice plate when compared to enclosure size and purge time desired.
c. Open the control unit door and make sure that the logic pressure gauge is holding steady between 25-35PSI or 1 ½ to 2 ½ bar. If this is the case the logics of the unit are running good and there may be three possible problems.

• Enclosure has too much leakage, check the door first
• The inlet pipe is too small or does not have enough pressure
• The pressure sensor has fallen out of calibration (Call Expo For help in checking this calibration. A Manometer is required)

d. Make sure that you have connected the Relief Valve (vent) to the flow sensor on the control unit using a minimum 1/8” pipe.
e. Make sure that enclosure is properly sealed. Note that although NEMA 4 cabinets are designed to keep water and dust from entering the enclosure they have not been designed to keep pressure from escaping. Pressure naturally bows the door and sides of the enclosure thus creating leaks. Example: 5 ft³ enclosure has one latch at center of door.
f. Inspect the enclosure for unnecessary leakage (i.e. unfilled conduit seals, unused holes etc….)

6. My leakage compensation (LC) systems goes all the way through the purge cycle and moves into leakage compensation mode for a few seconds. Then the pressure indicator goes off and the system jumps back into the purge cycle again. What should I do ?

This is probably because the Leakage Compensation valve is not set to top off for enough leakage. Try adjusting the valve counter clockwise to allow for more air flow in leakage compensation mode.

7. My gauge on the inside of my control unit starts out with 30 PSI and then drops either gradually or quickly to zero. It may also never show a reading. What is the problem ?

This gauge is giving us the status on the logics of the unit. If this pressure is gone then the regulator feeding the manifold with air is leaking or cracked. This could have happened from either over pressurizing the control unit or applying a contaminated air supply line to the control unit (i.e. oil, water, or dirt). You will need to replace the regulator (call expo for part number and pricing).