How do I Size a Maxitrol Gas Regulator?
- 1). Choose a regulator that has enough capacity to handle the flow rate. Size the regulator by making three separate determinations: inlet pressure available, outlet pressure desired, and the required maximum flow rate the regulator must handle. Use the Maxitrol pipe size, flow rate, inlet pressure, and outlet pressure numbers from the capacities and pressure drop figures found in their model charts.
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A 2 1/2-inch gas pipe is a relatively large gas flow pipe.Blue Meter image by Scott Griessel from Fotolia.com
Calculate first the available differential pressure. For instance, if the inlet pressure listed on the chart for a 2 ½-inch pipe is 9"wc, and the listed outlet pressure is -5"wc, the available differential pressure is 4"wc. Subtract the outlet pressure from the inlet pressure to find the available differential pressure, your first consideration for sizing the regulator correctly. - 3). Determine regulator capacity. Maxitrol recommends that the pressure drop be kept to half or less of the differential pressure. From the example given, the pressure drop to look for on the chart is 2"wc or less, half of 4"wc. Refer to the Maxitrol capacity chart to see which regulator has a pressure drop of 2"wc or less with a listed flow rate of 8,000 CFH.
- 4). Look on the chart for the regulator that matches the aforementioned criteria, and you will find that the RV111 has a flow rate of 12,134 CFH (8,000 CFH is well within this flow rate level) for the 2 ½ pipe size at 2"wc pressure drop. Consequently, only the RV111---2 ½", listed on the chart, is the correct size given the above criteria.
- 5). Study this example to see how to know the maximum recommended operating outlet pressure for a 4-inch pipe with a flow rate of 21,000 CFH and an inlet pressure of 10"wc. Look in the "Model Number and Pipe Size" column of the capacity chart for the listings of a 4-inch pipe. Right away you see the RV131 in the lower left corner.
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Flow meters monitor these pressure drops.pressure meter image by Thor Jorgen Udvang from Fotolia.com
Notice that the RV131 flow rate is 21,172 CFH with a pressure drop of 2"wc. Multiply this 2"wc times 2 to arrive at a differential pressure of 4"wc. Subtract 4" differential pressure from the 10"wc inlet pressure, and get 6"wc of maximum recommended outlet pressure setting which aligns with the chart.
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