Wet & dry sprinkler systems Continued from page 46
ential, you can hold back 6 psi of water pressure with only 1 psi of air pressure above the clapper. When a sprinkler operates, and the air pressure is lowered, the water pres- sure below the valve will eventually overcome the differ- ential and push the clapper of the dry valve open. This will allow the water supply to enter the piping network and be discharged from the sprinklers that have operated. This often brings the question from engineers, how much
air pressure is required to keep the dry valve in the set posi- tion? Using the 6:1 rule as an example, simply take the water supply pressure, divide it by 6 and add 15 to 20 psi for a cushion. Multiple manufactured dry valves may have a vari- ety of differentials: It is important to review the manufactur- er’s technical data, which often provides the proper air sup- ply requirements, based on your water supply pressure. When a sprinkler operates in a dry system there will be
a delay in full water flow, due to the travel time from the valve to the open sprinkler. NFPA 13 discusses require- ments for maximum water delivery in dry systems based on the total volume of piping4
. Accessories called accel-
erators are available to assist the speed of the valve oper- ation. Accelerators can help redirect air pressure in the system to lower the differential of the valve faster, which in turn speeds the operation of the valve. When putting a dry valve into service, you often need
to open the face plate of the valve and reset the clapper assembly inside. Newer valves can be reset externally,
eliminating the need to open the valve for any reason. After the clapper is set and the face plate is replaced, you are ready to introduce air into the system. Compressed air or nitrogen can be used to pressurize the dry pipe system. Riser mounted compressors are often used on smaller systems; however, tank mounted compressors with air maintenance devices are suggested for most applications. An air maintenance device helps to maintain the prop-
er air pressure in the piping and uses the supply within the tank to introduce more air to the system in the event of a small loss. Another option to consider are dryers installed on the air supply to remove any excess moisture in the piping. The trim piping installed on the dry valve offers the necessary pressure gauges, drains and pressure switches for water flow conditions. Other details of these systems are specific to various
manufacturers. I suggest that you take the time to review the equipment and installation requirements applicable to your system. n
Footnotes: 1
4
NFPA 13, 2010 edition, Section 1.1.1 2NFPA 13, 2010 edition, Section 3.4.10 3NFPA 13, 2010 edition, Section 3.4.5
NFPA 13, 2010 edition, Section 7.2.3. Todd Stevens, CFPS, is a national technical represen-
tative for The Viking Corporation.
CONNECTING STEEL PIPE JUST GOT EASIER
connect steel pipe: FASTLOCK™
Introducing a quick, easy way to securely , a complete line
of ½" – 2" malleable iron press fi ttings for schedule 10 – 40 black and galvanized steel pipe. FASTLOCK™
is
IAPMO and NSF-61-4 certifi ed for use with water, HVAC, and compressed air. Learn more at www.fastlockfi
ttings.com.
Circle 30 on Reader Reply Form on page 65 Page 48/Plumbing Engineer May 2011
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72