Book - School of Science and Technology

Corrosion 229Air bottleAir bottleMainMainLocked valvesFigure 8.28 Air bottles for high temperature systemscoming out of solution in the boiler. Elsewhere, if high points in the system cannot beprovided with air bottles having small bore vents to outside, then robust and simpleautomatic air valves, as shown in Figure 8.27, must be fitted. Centrifugal and other typesof air separators are sometimes added to domestic systems but there should be no need forsuch devices in a system which has been designed properly.For medium and high temperature water systems, where air release will ± inevitably ±be accompanied by some flash steam, full bore air bottles as shown in Figure 8.28 must beused with the discharge pipe led down to a position clear of any traffic. The needle valvefitted to the discharge pipe should be provided with a lock-shield type terminal or othermeans to avoid unauthorised use.System drainingOver the life of any pipework system carrying a fluid it will be necessary to replacecomponents, carry out repairs, make alterations, etc. To avoid the need to drain-downthe whole system to carry out localised work, isolating valves should be installed on bothflow and return pipes at strategic positions around the system, e.g. at floor branches offmain risers, enabling the section to be worked on to be isolated from the remainder.Within each section capable of being isolated in this way one, or a number of drain valves(cocks), each with a hose connection, should be provided at all low points to facilitate, asnear as practical, complete drain-down of each section.CorrosionA full scale treatment of this subject would be quite beyond the scope of this book aswould be any attempt at discussion in depth of water treatment and other ameliorativemeasures. It would, however, be wrong to ignore the subjects altogether in view of theirimportance: a reader in search of further information might refer either to the GuideSection B7 or, better still, consult a professional specialist adviser. The necessity to treat