To calculate the purging time on our 5500 series Type Z purge system, there are four variables that you need to know:
- The size of the enclosure
- What vent is being used
- What certification is desired
- What is the pressure inside of the enclosure
Each of these vents opens at a different back pressure, and each in turn has different flow rates. The differences in the three vents is noted in the chart below.
Each of these vents has 3 different flow charts that you can reference either in the manual or on the datasheet. The flow charts are based on the size of the enclosure that you are protecting. One graph is used when your enclosure is less than or equal to 5 cubic feet, one is used when your enclosure is between 5 and 15 cubic feet, and one is used when your enclosure is greater than 15 cubic feet. As an example, I have shown the EPV-5500…-01 graphs listed below.
Once you install the 5500 on the enclosure and provide air to the unit, you will be able to read what the pressure is from the LCD display on the 5500 Control Unit. For this example, our enclosure is 10 cubic feet. The chart to refer to is the one labeled “Enclosure up to 5-15 Cubic Feet”. The pressure reading for this example is 1.6” w.c. If you look on the corresponding flow chart, you can see that at 1.6” w.c. our flow rate is 9 SCFM.
The last piece of information you need in order to calculate the purge time concerns what certification is needed. You need to know this in order to determine how many volume exchanges need to be performed. For North American applications, 4 volume exchanges are required. With ATEX applications, 5 volume exchanges are required. For this example let's assume that this is a North American application and uses 4 volume exchanges.
You can now calculate your purging time. The formula to calculate the purging time is:
(Enclosure Size / Flow Rate) X Number of Volume Exchanges = Flow Rate
(10 cubic feet / 9 SCFM) X 4 = 4.44 (always round up to the nearest minute) = Purge Time = 5 minutes.