Unvented Cylinder Manual 09_12

3.12

3.12 DiscHArGe pipework note! tHe sAFety relieF vAlves Must not Be useD For Any otHer purpose 1) Discharge pipes from the temperature & pressure relief and expansion relief valve may be joined together. 2) The tundish must be vertical and fitted within 600mm of the temperature & pressure relief valve and must be located with the cylinder but away from any electrical devices. The tundish must also be in a position visible to the occupants, and positioned away from any electrical devices. The discharge pipe from the tundish should of metal and terminate in a safe place where there is no risk to persons in the vicinity of the discharge. 3) The pipe diameter must be at least one pipe size larger than the nominal outlet size of the safety device unless it's total equivalent hydraulic resistance exceeds that of a straight pipe 9m long. i.e. Discharge pipes between 9m and 18m equivalent resistance length should be at least 2 sizes larger than the nominal outlet size of the safety device. Between 18m and 27m at least 3 larger, and so on. Bends must be taken into account in calculating the flow resistance. See FiG. 3.11 and tABle 2. 4) The discharge pipe must have a vertical section of pipe at least 300mm in length below the tundish, before any elbows or bends in the pipework. 5) The discharge pipe must be installed with a continuous fall and should be at least one pipe diameter clear of the wall where it terminates. 6) The discharge should be visible at both the tundish and the final point of discharge, but where this is not possible or practically difficult; there should be clear visibility at one or other of these locations. Examples of acceptance are: i) Ideally below a fixed grating and above the water seal in a trapped gully. ii) Downward discharges at a low level; i.e. up to 100mm above external surfaces such as car parks, hard standings, grassed areas etc. These are acceptable providing that where children may play or otherwise come into contact with discharges, a wire cage or similar guard is positioned to prevent contact, whilst maintaining visibility. iii) Discharges at high level; Onto a roof capable of withstanding high temperature discharges of water 3m from any plastic guttering systems that would collect such a discharge (tundish visible). iv) Where a single pipe serves a number of discharges, such as in blocks of flats, i.e. into a metal hopper and metal down pipe with the end of the discharge pipe clearly visible (tundish visible or not). the number served should be limited to not more than 6 systems so that any installation can be traced reasonably easily. The single common discharge pipe should be at least one pipe size large than the largest individual discharge pipe to be connected. If unvented hot water storage systems are installed where discharges from safety devices may not be apparent i.e. in dwellings occupied by the blind, infirm or disabled people, consideration should be given to the installation of an electronically operated device to warn when discharge takes place. Note: The discharge will consist of scalding water and steam. Asphalt, roofing felt and non-metallic rainwater goods may be damaged by such discharges. 14

Temperature & pressure relief valve Metal discharge pipe (D1) from temperature & pressure relief valve. to tundish. 600mm Max. Tundish 300mm Min. Metal discharge pipe (D2) from tundish with continuous fall. See Table 2 and worked example. Discharge below fixed grating. (see page 10 for alternative points of discharge). Fixed grating FiG. 3.11 Trapped gulley tABle 2. Sizing of copper discharge pipe “D2” for common temperature valve outlet sizes. Valve outlet size Minimum size of discharge pipe D1* Minimum size of discharge pipe D2* from tundish G 1/2 15mm 22mm 28mm 35mm G 3/4 22mm 28mm 35mm 42mm G 1 28mm 35mm 42mm 54mm Maximum resistance allowed, expressed as a length of pipe (i.e. no elbow or bends) Up to 9m Up to 18m Up to 27m Up to 9m Up to 18m Up to 27m Up to 9m Up to 18m Up to 27m Resistance created by each elbow or bend 0.8m 1.0m 1.4m 1.0m 1.4m 1.7m 1.4m 1.7m 2.3m 15