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Testing Techniques Since the introduction of the new Water Regulations, the plumbers' attention has been drawn to items such as notification of work, pumped showers and WC flushing methods, but very little focus on the requirement for pressure testing. Within the new Water Regulations it is a mandatory requirement that: 'Every water system shall be tested'. Why mandatory testing? Traditionally, the plumber has not felt it necessary to pressure test; systems would simply be filled with water and the joints inspected. Half a century ago or more, this logic could perhaps be justified by the fact that most of the pipework could be visibly inspected for leaks. Today probably 90% of the piping joints in a typical new house are hidden during commissioning, so visual inspection of all joints is impossible. Yet the trend to have a cloakroom, second bathroom, etc dictates more piping. Also the popularity of mains fed systems, means that more assurance is desirable that the system will be safe at the peak mains pressure, which is not achieved simply by filling during normal working hours, when the pressure will not be at its highest. A second reason for testing is that the drains, sanitary pipework and gas pipework would normally be pressure tested, so why not test the water systems also? Water or air test? Some plumbers favour the use of air testing kits, as filling pipework with water whilst properly expelling the air is time consuming. However, testing with air is not an acceptable method in accordance with the Regulations and BS 6700: 1997. As air is compressible a leak comprising of a few droplets will be much more visual on a pressure gauge when testing with water. Some installers argue: ³We test both gas and sanitary pipework using air pressure, so why not water piping?² The answer is that both of these use a U-gauge as the measuring device, whereby a drop of only, say 5mm can be easily be seen. Such a drop equates to about 0.5 millibar, whereas the naked eye would struggle to detect a drop of less than 0.1 bar (100 millibar) on a typical pressure gauge! Therefore, the best test medium for water pressure piping is water; that is why the Regulations and BS 6700 both require 'hydraulic testing'. The need to pressurise Where joints are to be concealed, simply filling-up a system with water at normal pressure is not an adequate test. A poorly made soldered joint for example may appear to be satisfactory at the fill pressure, and detection will only be possible if the pressure is raised. Such a joint is often said to be 'hanging by a hare's breath', and needs additional pressure to expose the fault. The need for pressurisation is supported by the many acecdotal stories of unsoldered joints held together due to the sealing property of the flux alone. When to test The Regulations require that 'the whole system' is tested; taken literally, many installers may feel this to be unnecessarily onerous. In practice it would be sensible to test the 'first fix' carcass pipework before it is concealed. If this was done, then from a pragmatic view, is it really necessary to then re-test the whole installation on completion only for the sake of a few final connections, which can usually be visually inspected during commissioning? Further, if the hot and cold water is fed from gravity storage, then several temporary fittings will need to be employed in the vicinity of the storage cistern, in order to test as much of 'the whole system' as practical. When testing such systems it will often be necessary to carry-out two separate tests, as the hot water cylinder will not be able to withstand the test pressure required by the mains water supply. Direct mains water fed systems are invariably far easier to test, as on completed installations the hot and cold water can be temporarily linked-up in order to perform a single test. This can be achieved by making a temporary connection to the washing machine valves using appropriate hoses, as shown in the photograph (note also the size of the gauge). Filling for the pressure test Hand pump test kits are often needed in order to correctly pressurize the pipework, but they are not efficient for filling-up the system: most pumps will displace only about 25ml for each stroke of the pump! If a permanent water supply is not available in the plot, try to arrange a temporary hose connection as the method of filling the system. Practical tips The most common mistake, which installers make when testing, is they do not use a pressure gauge which is capable of giving an adequate response. Gauges that are not much bigger than a 50p coin are insufficient; the dial face should be not less than 80mm diameter. Also make sure the full-scale deflection is not excessively more than your test pressure, for example a gauge scale that goes up to 50 bar will not be responsive enough for your needs. Unfortunately most commercially available hand pump test kits are not fitted with an adequate gauge for thorough testing, and an extra test gauge should used between the test hose and point of connection to the system. Also you will need to detect pressure drops as small as 0.2 bar, so it would be preferable for the scale to have 0.2 bar graduations. The second mistake is not to expel the air during filling, as trapped air will make the gauge needle response 'spongy'. Installers often use blank caps to form temporary plugs, which is fine for pipework 'drops'. For upward facing 'tails' forming high points, the use of temporary couplings, which incorporate a drain cock, can be used to 'bleed' the air without causing excessive accidental spillage of water. When testing the 'first fix' pipework on new housing, the airing cupboard usually contains several upward facing pipe tails, which can be temporarily linked in order that all the circuits are tested in one operation. The temporary fittings employed for testing purposes can be re-used on other plots. Equator push-fit fittings can be re-used without the need to unscrew end caps or reassemble joint internals with new grip rings. The Equator range also incorporates plugs for push-fit sockets. The test method Most uninformed installers, if questioned about a suitable duration for a pressure test will often respond with a range of answers from 10 to 30 minutes. Such short periods are not sufficient to yield a thorough test. The Regulations prescribe both the method and the minimum duration for the test. The requirements vary depending on whether the piping is metallic or plastic. The reason for this is that plastic piping has elastomeric properties when subjected to pressure. There are also two optional test methods for plastics; a summary of the requirements is given in the Table below. It should be noted that there is a discrepancy between the Regulations and BS 6700 related to the final pressure in the plastics Test A method. BS 6700 recommends the pressure be reduced to one half the test value, whereas the Regulations state a value of one third. From a practical view, the final test value used is not important; it is more critical that the test is properly undertaken. No substitute for quality A common misconception held by some construction supervisors is that a 'Pass' on a pressure test record sheet signifies that the system was correctly installed. A satisfactory test result merely indicates that the system is currently watertight and is likely to remain so for the foreseeable future, providing that: 1. The test was properly undertaken. 2. The standard of workmanship for the installation was adequate. Clearly the requirement for pressure testing should not be seen as a reason to take a relaxed view on the need for quality control measures, or on the importance of selecting competent installers who fully appreciate the products they are using. A Distance Learning booklet is freely available from Marley to cover product awareness aspects of the Equator push-fit hot and cold water system. The booklet can be obtained by dialling a free phone literature hotline 0800 0281 876. It is wrong to think that there is more need to test plastic systems than copper systems, the Regulations require all systems to be tested. Reproduced courtesy of Plumbing, The Institute of Plumbing's Magazine. By Brian F Whorlow IEng FIOP RP, |
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