09252018Tue
Last updateTue, 25 Sep 2018 8pm

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Where Valves Are Used

Behind the Walls: Valves in Building Systems

13wnt building systems 1Equipment used in running modern office building water and air conditioning systemsToday’s building systems move many types of fluids and gases through their lines to keep operations such as HVAC, fire protection, water and waste­water functioning. Valves play a key role in keeping those systems flowing.

 

Commercial buildings are all around us, but unless we pay close attention during their construction, we have no concept of the multitude of fluid arteries hidden within the walls of masonry, glass and metal. Those pipelines carry everything from water to critical gases, and the buildings couldn’t function without them.

The common denominator among buildings is water—all commercial buildings contain piping systems carrying many combinations of the hydrogen/oxygen compound in the form of potable water, wastewater, hot water, grey water and fire protection.

SAFE FROM FIRE

From a building’s survival standpoint, fire protection systems may be the most important of the water systems. Fire systems in buildings are almost universally fed and filled with clean water. For these systems to be effective, they must be reliable, have sufficient pressure and be conveniently located throughout the structure. Two primary systems deliver this combustion-quenching liquid: sprinkler systems and hose connections.

The sprinklers are usually installed in the ceiling of each floor. These systems are designed to automatically energize in case of a fire. Hose connections, which are called standpipes, exist at various locations in a multistory building and are designed to extend the reach of a fire department’s hose without having to drag hoses up into tall buildings.

Design and installation of fire sprinkler systems, including valving, is directed by the National Fire Protection Association (NFPA) document 13, Standard for the Installation of Sprinkler Systems. Additional NFPA standards cover different aspects of fire protection piping.

The two water arteries of sprinkler and standpipe lines have to have sufficient water pressure to provide the necessary flow to fight a fire. For low-rise structures, the piping pressures are nominal, usually less than 100 psi, so many different materials of construction will suffice. However, ductile iron and bronze are the materials of choice because of their low cost and ease of manufacture.

In general, city water supplies are in the 40–100 psi range, which is sufficient for fighting fires in most low-rise buildings. But what happens when the building is higher than that? To answer that question, we need a little refresher on physics and gravity.

Each foot of height provides or consumes .43 psi of pressure, so an average pressure loss for a 12-foot floor is about 5.16 psi. For this reason, pumps have to be used to energize the lines and provide the minimum sprinkler operating system. Where these pumps are placed depends on the height of the building. In the case of very tall, high-rise buildings, pumps and related piping move into the 300–600 psi working pressure range. This higher pressure requires higher-rated piping components, including valves. In many older buildings, a water tank has been located on the rooftop to provide immediate water pressure for most floors. However, the water tank first has to be filled via a pumping system.

CLEAN WATER

While fire protection water may be the most vital water in a building’s piping system for safety reasons, the buildings could not function without potable water. Clean water is used for drinking, restroom facilities and a host of other building needs. Piping for these systems follows the general tenants of firefighting piping, in that iron and bronze are used, and pressures are moderate. Both firefighting piping and water piping predominately use grooved mechanical connections on their pipes, valves and fittings. These mechanical joints, as they are sometimes called, have some flexibility, as well as the ability to adjust for small miscalculations in piping alignment. In areas that are earthquake-prone, the grooved piping also handles the shakes and sways so that pipes don’t break.

LOW-LEAD REQUIREMENTS

13wnt building systems 2Bronze is the material of choice for many of the low-temperature, low-pressure valve applications in building systems. Bronze is well-suited for lower temperature steam and water service.Speaking of earthquakes, a man-made shake-up has occurred in the clean water industry recently in the form of an amendment to the Safe Drinking Water Act that limits the amount of lead in potable water piping systems components, including valves. Effective Jan. 4, 2014, the maximum allowable lead content in pipe, valves and fittings in drinking water components will be limited to .25% by weight. This has required a major change in the chemistry of the cast bronze material used to make valves. (The previous lead limit as listed in ASTM B61, Standard Specification for Steam or Valve Bronze Castings, was 3%.)

When a building’s water system is connected with the city water supply, contamination is always a concern. The clean water in the mains can be at risk if contaminated or non-potable water in the building’s water system is drawn back into the main. To prevent this, plumbing engineers resort to backflow prevention technology. These devices are usually made up of valves in series, including two check valves. The devices ensure that any downstream overpressure or upstream vacuum will not draw unwanted water back into the clean water stream. Nearly every plumbing code requires the use of such devices.

13wnt building systems 3Chiller systems for HVAC applications often contain many valves. This image shows part of the piping system on an industrial chilled water system.HVAC

Although water systems are the main focus of general commercial piping, they are not the only fluid plumbing engineers must focus upon. The heating, ventilating and air conditioning (HVAC) side of buildings has its own complex piping system and valves.

The oldest HVAC fluid is steam, which has been used in heating systems for over 100 years and is still very popular in the northeast. Direct steam heating uses low-pressure steam provided by an in-house boiler or purchased from a municipality. The steam is piped throughout the building and regulated into radiators to disseminate the heat.

If steam is generated on site, the boiler and associated equipment is valve intensive. These boiler systems are treated just like their big brothers at the power plant so high-temperature steel valves and piping are normally used. Class 300 steel valves are very popular in this type of application.

As an alternative to steam heat, many facilities use hot-water climate control systems. The lower-than-boiling-point hot water systems require a much less robust piping system than what is used for steam. Elastomer-seated ball valves and rubber-lined butterfly valves are often used in this service, with bronze and iron the material of choice.

For large-scale commercial and industrial air conditioning systems, a central chilling unit often is em­ployed. These central units distribute chilled water at about 40°F (4°C) to each desired location. An additional line returns the warmed water to the chiller to be re-chilled and used again. Valves for chiller applications are mainly quarter-turn types, with the butterfly valve being the first choice of HVAC piping engineers. A large ­central facility such as those found on college campuses or in medical complexes could contain miles of piping and hundreds of valves.

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