BS 750:2012 pdf download – Specification for underground fire hydrants and surface box frames and covers 4.3.3 Materials 4.3.3.1 All copper alloy materials used in the construction of fire hydrants shall conform to BS EN 1982, BS EN 12163, BS EN 12164, BS EN 12165, BS EN 12167 or BS EN 12168. 4.3.3.2 The threaded part of the valve that engages with the stem shall be copper alloy. 4.3.3.3 All components of the valve operating mechanism shall consist of materials that avoid the risk of corrosion or galling resulting in seizure or mechanical failure. 4.3.3.4 Stems of type 2 fire hydrants shall be manufactured from stainless steel conforming to BS EN 10088-1 with a minimum chromium content of 13%, or copper alloy (see 4.3.3.1). 4.3.3.5 Stainless steel outlets shall be manufactured from grades conforming to BS EN 10088-1 with a minimum chromium content of 13%. 4.3.4 Sealings Stem sealings shall be of one of the following two types: a) toroidal sealing ring (“O” ring) type; or b) other pressure actuated types of seal. Stem seals located within the pressure retaining body of the valve shall be maintainable, in situ, while mounted in a chamber with a surface box frame and cover in accordance with Clause 14, and depressurized at the point at which the replacement is being effected. Where stem sealing is of the toroidal sealing ring (“O” ring) type, two such seals shall be used. A wiper ring shall be positioned above the seals to prevent the ingress of foreign matter. 4.3.5 Bonnets Bonnets connected by means other than those described for type 2b and type 2c shall be secured by two independent and functionally different means. These different means shall each be capable of preventing the bonnet becoming unintentionally detached in the absence of the other. Components involved in the attachment or retention of fire hydrant bonnets shall not be made from plastics. Bonnets connected by means other than those described for type 2b and type 2c shall conform to the type requirements in Clause 10 with: a) both security systems in place; b) only one of the security systems in place; and c) only the other security system in place. 5 Outlets 5.1 The outlets shall be manufactured from copper alloy or stainless steel materials conforming to 4.3.3 and shall conform to 10.3 and 10.4. The outlet shall conform to the dimensions shown in Figure 3. 5.2...
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