SPONSOR CPD PROGRAMME Continuing professional development (CPD) is the regular maintenance, improvement and broadening of your knowledge and skills, to maintain professional competence. It is a requirement of CIBSE and other professional bodies. This Journal CPD programme can be used to meet your CPD requirements. Study the module and answer the questions on Isolation valves for HVAC pipework systems completed module is equivalent to 1.5 hours of CPD. Modules are also available at www.cibsejournal.com/cpd This module explores the use of isolation valves in domestic and commercial HVAC applications This CPD introduces isolation valves (IVs) that are likely to be found in domestic and commercial HVAC applications. IVs are essential components of every piping system, to allow selective isolation of sections for on-off control, maintenance, removal, and commissioning. There are numerous IVs employed in a commercial system and, as illustrated in Figure 1, even a relatively small sub-system of lowtemperature heating distribution pipework serving two fan coils will include in the order of 10 IVs. The selection of appropriate IVs is based on parameters that relate to the specific application including the size and type of pipe and the operating pressure inside and across the valve; these are discussed in the boxout DN and PN for pipework components. The most common types of isolation valve employed in general HVAC applications are ball valves and butterfly valves. These are well suited to the traditional low-temperature hot water (LTHW), chilled water (CHW) and domestic hot and cold-water services found in commercial and domestic applications and when closed, they offer a tight seal at their rated differential pressures. Ball valves are commonly available in sizes 15mm to 50mm, and are often applied in LTHW, CHW and domestic systems. As illustrated in Figure 2, the ball has a channel through its centre, and the valve stem engages with and rotates the ball. Rotating the ball will vary the degree of opening and with a quarter turn will change the fluid flow path from, typically, full bore to fully closed. (Full bore valves will cost more than reduced bore valves but provide less turbulence and a higher valve coefficient (Kv), so lower operational cost. For an explanation of the impact of Kv see the boxout The cost of pumping through valves and fittings.) An example of a 50mm ball valve has a Kv of approximately 300-400. The ball floats in the space created by the seals (typically polytetrafluoroethylene (PTFE)) that also provide the bearing for the ball. Water trapped in the channel (within the ball) when the valve is closed can present a risk of freezing and potentially cause splitting of the body, so requires appropriate protection. Ball valves are normally operated with a hand-operated lever, or they can be automatically controlled with an actuator. As well as circuit isolation, these are often applied as flushing valves, as in Figure 1, to isolate significant plant items when flushing and cleaning. Their robust construction ensures a long, trouble-free service life, producing minimal turbulence in the open position and tight closure in the closed position. Unless specifically designed to do so, possibly with specifically designed, characterised inserts, a ball valve should not be used as a throttling (regulation) valve. Butterfly valves, as in the example illustrated in Figure 3, provide a compact solution consisting of a disc that rotates on a shaft at right angles to the fluid flow. When open, the disc is edge-on to the flow and the fluid passes around it, offering limited resistance an example 50mm butterfly valve has a Kv of approximately 100. These shut off with a quarter turn, either using a direct, simple spindle or employing a gearbox for larger valves. In the closed position, the www.cibsejournal.com October 2021 73 CIBSE Oct21 pp73-76 CPD 185.indd 73 24/09/2021 14:27