PRVs and pressure control valves have other <br />disadvantages. Their failure rate has been high, <br />resulting in the addition of testing requirements to <br />NFPA 14. Secondly, many cannot be adjusted by <br />firefighters during a fire, or they require special <br />tools and knowledge. Finally, hose connections <br />with these devices cannot be used as backup fire <br />department inlet connections, since water can only <br />flow through a PRD in one direction. <br />The most reliable means of limiting pressures in <br />standpipe systems is to design them to preclude <br />the need for pressure regulating devices. In shorter <br />buildings, careful attention to the design of pumps <br />and the maximum pressure supplied by incoming <br />water mains can accomplish this. In taller build- <br />ings, the same concept can be applied to each sep- <br />arate vertical standpipe zone. Pressure fluctuations <br />in the water supply as well as the full range of fire <br />pump capacity are essential considerations in any <br />building. <br />If the use of PRDs cannot be avoided, certain <br />design features will balance their disadvantages. <br />The easier the valves are to adjust in the field', the <br />faster the fire service can overcome any unforeseen <br />situation. Designers should select valves which can <br />be easily adjusted and specify that identification <br />signs and adjustment instructions be posted at <br />each valve. The tools required to perform field <br />adjustments should be kept in a secure yet accessi- <br />ble location such as the fire command center or <br />a locked cabinet near the fire alarm annunciator. <br />Finally, a supplemental system inlet should be pro- <br />vided at the level of 'fire department entry. This can <br />be simply an extra hose connection without a ?RD <br />on a riser. NFPA 14 recommends a supplemental <br />inlet, and it is especially important for systems with <br />a single fire department connection. <br />Considerations - Pressure Regulating Devices <br />■ Design to preclude the need for PRDs. <br />■ Specify the highest and lowest possible inlet <br />pressures at each PRD location. <br />■ Select devices capable of simple emergency <br />adjustment. <br />■ Post identification signs and adjustment <br />instructions. <br />■ Provide adjustment tools in a secure, acces- <br />sible location. <br />■ Provide backup inlet connection at fire <br />department entry level. <br />STANDPIPE ISOLATION VALVES <br />The considerations in the section, Water Supply <br />Control Valves, on page 29, apply to standpipe sys- <br />tems as well. This section gives additional guid- <br />ance on valves specific to standpipe systems. <br />The vertical pipes that feed hose connections <br />are called standpipes or risers. If there are multiple <br />risers, NFPA 14 requires interconnections with sup- <br />ply piping to form a single system, with valves at <br />the point where each riser is fed by the main bulk <br />piping coming from the water supply point. <br />Designers should also put valves on the feed lines <br />to remote or supplemental hose connections (see <br />Fire Hose Connections, page 34). <br />These valves are all called "standpipe isolation <br />valves." The ones on vertical risers are called "riser <br />isolation valves. " They allow the fire department <br />to shut off, or isolate, any given riser or feed that <br />breaks or otherwise fails. Firefighters may then use <br />the remaining standpipes. <br />(Fig. 4.11) Isolation valve between the feed main (enter- <br />ing from the lower left) and the vertical riser (on the <br />right). It is located within the stair enclosure for protec- <br />tion. The valve at the top of the photo is a sprinkler zone <br />control valve. <br />I <br />TIRE SERVICE FE;ATURES OF BUILDINGS AND FIRE PROTECTION S'Y.STEMS 38 <br />155 <br />