Installation
Installation
Hence L = L x 0.75 x l x T L = Change in length in mm. L = Length between two points in m. l = coefficient of expansion (HDPE 0.2 mm/m °C) T = temperature difference in °C T depends on the type of pipework:
7.2.1 Flexible
expansion socket is provided on each storey, with the floor of each storey serving as the fixed point. In order to allow the pipe room for expansion it must not be inserted right up to the stop in the socket. The free length within the socket is dependent upon the temperature during installation. Expansion sockets are available with the insertion length stated in relation to the ambient temperature during installation. Since the socket end always points upwards it is possible that soiling will enter the socket via the pipe from outside during construction. This can be prevented by sealing the socket with tape. Expansion sockets should be placed as close as possible to the least moveable side connection. In residential properties this will be the toilet connec- tion. The expansion socket is then located directly above the toilet connection T-piece (illustration 7.3). Using couplers With HDPE pipework, if the socket is firmly attached to the pipework, the fixed point clamp must be placed by the socket. With a permissible L of 10 mm, the per- missible pipe length for "cold" pipework is L = 10 mm = L x 0.75 x 0.2 x 20. L = 3.33 m. With "warm" HDPE pipework L = 1.66 mm. With this type of pipework it is important to prevent grit entering the pipes. The sliding back and forth in the rubber seal can in time allow grit to enter between the pipe wall and the rubber seal, causing leaks.
installation Flexible installation means that pipe lengths determined in advance can easily be shortened or lengthened. They slide through support brackets. The change in length is taken up by expansion sleeves or flexible connectors. In order to achieve this, clamping brackets are used as fixed points at the expansion socket or flexible connector. Fixed points can also be achieved by casting-in elements of the pipework (illustration 7.2). It is recommen- ded that expansion pieces should be used only in vertical pipework and flexible connectors in horizontal pipework.
cold pipework T = 20°C warm pipework T = 40°C hot pipework T 60°C
Modifications to the building or its use may alter the temperature range. Sufficient safety must therefore be incorporated into the building. Good routing of pipework can be of assistance here. This allows maximal freedom of movement so that the minimum tension or elongation arises in the material. Small diameter pipework may sag when warm or hot, so that the necessary fall is lost. It is then sometimes necessary to provide continuous support to the pipe- work. Support with half-shell brackets is recommended for HDPE-pipework (illustration 7.8). The pipework will generally not move easily if half-shell brackets are used. This can therefore not be termed flexible installation. 7.2 Installation methods The installation method is determined by the manner in which the changes in length resulting from temperature fluctuations are taken up. Two possible methods are available: Flexible installation, divided into: - flexible installation with expansion sleeves and compression sockets - flexible installation with flexible connectors Rigid installation
Illus. 7.1 Relationship between bracket separations, pipe diameter and suspension forces with filled HDPE pipework.
- Flexible installation with expansion sleeves and couplers
Illus. 7.2 Fixed points and fixing points via casting-in.
7.1.3 Freely suspended pipework - Temperature differences. Plastics have a fairly high coefficient of thermal expansion. For HDPE it is 0.2 mm/m °C. Pipework will therefore become longer or shorter through temperature fluctuations. Extreme temperature fluctuations may also arise during construction, from 50°C in the sun to -20°C in winter when sites shut down. Temperature fluctuations arise during use, from the varying temperature of the discharged water and of the environment. 40°C may be adopted as a maximum mean temperature difference in the walls of connecting pipes and collecting pipes for domestic above- ground drainage, even where occasional brief discharges of waste water at 80°C to 90°C occur. A 20°C temperature diffe- rence can be adopted for stacks and underground pipework. Note: This relates to the mean wall temperature along the full length of the pipework; the variation in discharge temperatures may be far greater. For extended discharge of large quantities of hot water a 60°C temperature difference may be adopted; HDPE will usually be selected for such
With expansion sleeves There is a risk when expansion pieces are used horizontally that fouling will occur between the socket and the pipe. Use of expansion pieces is therefore recommen- ded only in the case of vertical pipework. For the same reason expansion sockets should be fitted with the socket end upwards. Expansion sockets are fixed with fixed point brackets above which the pipe must be free to change in length. A sliding bracket is therefore generally used to support the socket. Good align- ment is important. The pipework between the expansion sockets must be resistant to tensile stress. As a rule of thumb, the length between expansion sockets is generally 6 m for HDPE, provided there are no side connections. In practice an
applications, as the medium temperature exceeds 70°C. Temperatures may vary widely for rainwater drainage under the roofs of large buildings. It is recommen- ded that 40°C to 50°C be taken as air temperature and +5°C as water temperature in winter rain. The effective temperature difference is then around 35°C. The largest variation in temperature in rainwater downpipes on walls will arise when the water is not drained off. Large temperature differences can occur under the influence of frost and sun and a maximum variation of 60°C can be reckoned upon. Through this temperature difference pipework will become shorter or longer. Practice shows that the difference in length will be around 0.75
Illus. 7.3 Expansion socket at the least moveable side connection.
times what was calculated. We can distinguish between cold pipework
(max. temperature difference 20°C), warm pipework (max. temperature difference 40°C) and hot pipework (max. temperature difference 60°C). These dis- tinctions apply to domestic discharges. In the case of extended discharges of large quantities of (hot) water the categorisa- tion should move up one place.
The method to be employed is determined by the designer.
24
25
Made with FlippingBook Annual report