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E4) Air Leakage Test of the uPVC Combined Stack System I.K. Chan*, Eric S.W. Wong*, Henry C.K. Hung*, Kenny M.B. Wong* *The Chartered Institute of Plumbing and Heating Engineering, Hong Kong Branch info@ciphe.org.hk Abstract After the SARS outbreak in 2003, more attention has been paid to the potential problems caused by improper functioning of the uPVC effluent discharge piping system. It was found that the cause of rapid spread of SARS disease was due to the malfunctioning of traps in the soil discharge systems in a residential building. Hong Kong is a densely populated city. High-rise multi-storey buildings are built densely and close to each other. As such, dispersion of contaminated air leaking from the malfunctioning combined stack piping components was not easy, especially in the windless weather condition. The densely populated urban area faces a shortage of fresh air ventilation for dispersion of the contaminated air from the combined soil stack. In Hong Kong, uPVC piping system is used in most of the residential buildings for drainage. The ideal uPVC effluent discharge piping system should be water-sealed and air-leak proof. The perfection of the uPVC discharge piping system can hardly be achieved due to the following main reasons: • The manufacturing imperfection in the piping fittings and piping design. • Improper installation of the piping fittings and poor workmanship. This article is to investigate The source of contaminated air leakage from a typical residential uPVC piping

system. Laboratory test results and findings will also be demonstrated. Justify the methodology, practicability and the degree of acceptance by the industry

for adopting the following sanitary piping testing methods Keywords Combined soil stack, uPVC pipe, water seal, air-leak proof, malfunctioning of traps

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1. Introduction 1.1 Background Hong Kong is a densely populated city. The densely populated urban area faces a shortage of good air ventilation for dispersion of the contaminated air from the combined soil stack. After the SARS outbreak in 2003, more attention has been paid to the potential problems caused by improper functioning of the uPVC effluent discharge piping system. It was found that the cause of rapid spread of SARS disease was due to the malfunctioning of traps in the soil discharge systems of a residential building. The ideal uPVC effluent discharge piping components should be water-leak proof and air-leak proof. The perfection of the uPVC discharge piping system can hardly be achieved due to the following main reasons: 1.1.1. The manufacturing imperfection in the piping fittings and sealing design. 1.1.2. Improper installation of the piping fittings and pipe works. 1.1.3. Poor workmanship. This article is to investigate the source of contaminated air leaking from the uPVC piping system. Laboratory test results and findings will also be demonstrated. 1.2 Objective of the Tests The objective of the tests is to justify the methodology, practicability and the degree of acceptance by the industry for adopting the following sanitary piping testing methods: 1.2.1. Low Pressure Air Test (generally in accordance with BS5572) 1.2.2. High Pressure Air Test (generally in accordance with USA practice) A typical 1:1 scale model including branch pipes was set up for the tests. The air leak test was applied to uPVC pipes for the verification of air-tight pipe joints and U-traps. The possible difficulties when the proposed testing methods were being carried out and the proposed precautionary measures to prevent the corresponding difficulties were both discussed. 2. High Pressure Air Test In order to be in line with the sequence of erecting the sanitary piping on site, the order of tests is recommended as follows: High air pressure test went first (all sanitary appliances were uninstalled, the sanitary system was still dry and all the traps were sealed before applying high pressure air at 0.34 Bar to the system) Finally, low air pressure test (all sanitary appliances and traps were installed and the sanitary system were charged with water)

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High Pressure Air Test was used to test the air-tightness of uPVC pipe joints and uPVC fittings of all above ground sanitary pipework The test was conducted on completion of all external and internal pipework while leaving all sanitary appliances un-installed. A high internal air pressure (i.e. 34kPa or 3.4m w.g.) and a longer testing period (i.e. 15 min.) was applied to the drainage piping system. A higher standard in workmanship and a more reliable system for leakage free were established with the installation of the High Pressure Air Test in the drainage system. The drawing (Fig 1) below showed the schematic of the uPVC drainage under high pressure test

Fig 1 showed the schematic of the uPVC Fig 2 Insertion of rubber ball into the vent drainage system under high pressure test. Stack for sectioning the tested floors For detail please refer to appendix 1

2.1 Set up and Procedures: i) All the open ends of the pipework were plugged off with pipe caps/plugs. ii) Smooth surface rubber ball with diameter close to the uPVC pipe internal diameter were inserted into the pipework and vent stack through the access fitting. A stopper (see figure 5) was placed to prevent the ball from slipping away under high pressure. The ball was charged to a pressure of about 0.3 Bar so that its surface is strongly pressing against the internal surface of the PVC pipe. A small amount of water was filled to cover the ball sufficiently in order to provide perfect air seal.

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Fig 3 Cover the inflated ball with water for perfect air seal iii) The electric air pump discharge was connected to the inlet of the air control valve combination set (fig 4). The outlet of this set was connected to the air inlet valve at the W.C. drainage pipe. This air control valve combination set was to control the air pressure to the uPVC piping under test. The air pump discharge valve was opened slowly. If there was air leakage, the pressure dropped quickly when air pump was switched off.. The rate of pressure drop showed the seriousness of the air leakage. After repairing all the leakage points, the result was considered satisfactory if the pressure (i.e. 34 kPa / 0.34 bar) inside the uPVC pipework can sustained for 15 minutes after shutting off the air pump.

Fig 4 Air control combination set Fig 5 PVC stopper is inverted to prevent sectioning ball

slipping away under pressure iv) Soap bubble solution was used to test the air leakage points 2.2 Test Result

Figure 6 The photo showed that with the air pump running, the air pressure indicator can only be maintained at a pressure of 0.1bar although the maximum air pump capacity can reach to 0.35 bar. If there was air leakage the pressure indicator returned to zero immediately when the running air pump was switched off.

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Figure 7 After repairing all the air leak points, the highest reachable test pressure was only 0.3 bar (30kPa). Just after 0.3 bar, all the sectioning rubber balls were suddenly forced out of their position under the great air pressure (0.3 bar)

In this high air pressure test, the reachable air pressure inside the uPVC pipework was only 30 kPa for 15 minutes after all the suspected leakage defects had been repaired. There were a number of air leak points found including:

Figure 8 The leakage at the expansion joint Figure 9 The leakage at the bottle trap was due to poor workmanship in applying PVC solvent cement.

Figure 10 The air leakage at the cleaning eye cap due to moulding defect 2.3 Analysis of high pressure Test Results The test results showed that there were a lot of defects coming from the following

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sources. They can be divided into two kinds of sources: The air leak points in the uPVC components including: i) The sealing seat protrusions on the cleaning eyes and access fittings by moulding process. These defects cause air leakage through the sealing gasket ring. ii) The structure of the bottle trap was not strong enough for tightening the sealing ring. Slipping on the tightening thread sometimes occurs. iii) Installation defects from the workmanship of the plumber: It was found that the uPVC piping system could only withstand a pressure of 0.3 bar. Just after 0.3 bar both the upper and lower sectioning rubber balls were forced out of its original position suddenly! It may be due to the fact that wet uPVC pipe internal surface was quite slippery. Under such a pressure of 0.3 bar the friction between the ball and the uPVC pipe cannot hold the ball and slipping of the balls suddenly occurred. It was strongly recommended to insert a uPVC pipe stopper through the access fittings (fig 5) so that once the ball slipping occurred under a high pressure the stopper can stop the ball movement as showed in fig 5. In this test the sudden ball slipping occured at a pressure of 0.3 bar. At the beginning of the test, there were serious leakages, and the pressure gauge can only reach a pressure of 0.05 ba.Only After all the leakage points has been checked and repaired, the pressure can gradually increase from 0.1 bar to 0.3 bar. 3. Low Pressure Air Test Low Pressure air test was used for the test of air-tightness of pipes and fittings of all above ground sanitary pipework and above the lowest appliance. The test is to be conducted on completion of the whole drainage installation including external and internal pipework with all sanitary appliances installed.Fig. 11 below showed the schematic of the uPVC drainage under low pressure test.

Figure 11 The schematic of PVC Figure 12 Insertion of rubber ball into the drainage under low pressure test vent stack for sectioning the tested floors Details are shown in Appendix 2 3.1 Test Setup and Procedures for low pressure test i) All seal traps of sanitary fittings (including water closet, wash basin, floor drain, shower tray and washing machine) were charged with sufficient water. The rubber balls were inserted into the pipework and vent stack through the access fittings to section the

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tested floors. The rubber balls were inflated to a pressure of about 0.3 Bar so that its surface was strongly pressing the internal surface of the pipework. A stopper was placed (showed in fig 5) in order to prevent the rubber balls from moving away. ii) The air pump and manometer were connected to the system by flexible tubing. The air pump discharged air into the uPVC pipework through a specially designed spring tube. This spring tube was inserted into the pipework of the drain stack through the W.C. as shown:

Figure 13 The spring tube was inserting into the combined stack through the W.C. iii) Specially designed spring tube was used so that it can bend and pass through the u-shape pipeline without tube collapsing causing air blockage. iv) The electric air pump discharge was connected to the inlet of the air control valve combination set (fig 4). The outlet of this set was connected the spring tubing and the manometer. Spring tubing was inserted into the drain stack through the lower level W.C. v) After all preparation has been connected and checked, the manometer inlet valves should be closed temporarily for purging procedure to ensure that no residue water in the flexible spring tubing. After purging the manometer valve can be opened slowly and the air pump outlet valve should be adjusted carefully so that a 150-mm w.g. pressure should be obtained. If the applied air was too much, water in the traps will rise up and finally excessive air from the air pump will escape from the u-trap so that the water gauge pressure can hardly reach 160mm for 80-mm traps. The air pump outlet should then be turned off. If there was any air leakage defect, the manometer reading will drop gradually. If this happened, the air pump should be turned on again and the leakage defects should be located by jetting the bubble solution to the suspected leakage locations while the air pump was running. After repairing all the defects and there was no air leakage, the manometer reading should be able to sustain a constant reading of at least 38mm w.g. for 3 minutes. The drop in pressure was recorded. The test was considered satisfactory when the pressure (at least 38mm w.g.) can sustained for three minutes with the air pump stopped running. 3.2 Low Pressure Test Results The low-pressure air test was completed in this test. In this test, soap bubble was applied for easier detection of leakage. Besides, a higher air pressure of about 150mm w.g. had been supplied from the air pump in order to provide a more obvious bubbling

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detection. Although the applied air pressure was not as high as the high pressure air test, air leak defects can also be located by the air bubble method as shown below:

Figure 14 The big soap bubble was formed under a testing air pressure of 38mm w.g. on a loose cleaning eye cap. This showed that the low pressure air could also identify air leak defects After all the defects on the pipework components were all solved, a pressure of 38mm w.g. in the uPVC pipework can sustain for a 3 minute period after stopping the air pump.

Figure 15 L A 38mm w.g. test pressure can be maintained for 3 minutes after the air pump was

switched off. Figure 16 R The above photo showed that once pressure in the pipe was broken by pushing the

anti-siphon valve, the manometer reading dropped to zero immediately After the 38 mm air pressure test was witnessed and verified, the above witness tried to depressurise the uPVC pipeline by pushing up the anti-siphon disc guide pin. The manometer reading returned immediately to zero after depressurization. This also proved that sealing function of the ant-siphon valve was good for its sealing function under a 38mm w.g. test air pressure. The above photo showed that once pressure in the pipe was broken, the manometer reading was back to zero immediately. If the manometer reading cannot return to zero after depressurization by opening one of the sealing, there may be some kind of tricky suspect. 3.3 Analysis of Test Results The low-pressure air test can locate a major air leak defect using bubble solution. The air leak defects include the serious leakage defect on the expansion joint, and the workmanship defects leading to a more serious air leak. If the defect is minor, such as the cleaning eye defect by the moulding extrusion, the low-pressure air method can hardly locate these minor defects. These hidden defects are mainly due to the manufacturer’ mould defects. Due to the mass-less property of the air, this testing can be theoretically applied to the whole installation but there will be more leakage detection difficulties for detecting the whole installation in one test.

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4. The functions and installation of uPVC drainage traps with an anti-siphon valve 4.1 Function of the anti-siphon valve The following picture shows the schematic structure of the anti-siphon valve. The purpose of the anti-siphon valve is to break the partial vacuum created when there is a fast water flow down the main stack based on the Bernoulli’s principle of flowing fluid. Moreover, when the soil stack momentarily exceeds the design flushing water flow rate, the flush water mass can fill up part of the soil pipe. This mass of water compresses the air in front of it and creates a partial vacuum behind it. So that the pressure at the drain trap outlet always fluctuate about the vented atmospheric pressure with transient positive and transient negative fluctuation. An excessive siphon action will have the danger of exhausting the water inside the water trap as shown . The water sealing between the drain inlet and the main stack cannot function properly if the U-trap is dried.

Figure 17 Proper installation of U-traps for sealing the floor drains from the main stack It is verified that the air valve of anti-siphon U-trap is able to keep closing tightly under the positive air testing pressure. The copper sealing valve disc can provide rigidity against deformation under positive air pressure. But it is found that the efficiency of the anti-siphon depends on both the design and the aging of the anti-siphon valve. As seen in the following short video film

Figure 18 and 19 Anti-siphon rubber valve disc was found stained at valve seat side Performance test of a bottle U-trap found in the debris of renovation dumping site

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Figure 20 A functional anti-siphon copper valve disc with gasket lining Performance test of a good bottle U-trap used in the uPVC pipe test 4.2 Calculation of optimum weight of copper disc In the following calculation we would like to determination of the optimum weight of the anti-siphon valve disc that could sustain the 38 mm - 50 mm water gauge air pressure without affecting the operational performance of the U-trap under normal operational condition. The suitable weight of the copper disc is to ensure the rapid return of the air-valve to its sealing position under the gravitational action. The mass of the anti-siphon valve, based on copper disc valve, was plotted against suction pressure as follow:

Figure 21 The mass (in grams) of the anti-siphon valve was plotted against suction pressure (mm w.g.) 5. Conclusion 5.1 High pressure test In the high pressure test it was found that the air bubble method was very effective in detecting air leakage defects. High air pressure was strong enough to form soap bubble from the minor defective point. If there were air-leakage defects in the uPVC pipe system, the pressure inside the uPVC pipework dropped rapidly immediately after shutting off the air pump. Only after all the leakage points have been checked and repaired, the pressure can gradually increase from 0.1 bar to 0.3 bar (i.e. 34 kPa / 0.34 bar/3.4m w.g.) and maintained the pressure at 0.3 bar for 15 minutes with the air pump stopped running.

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5.2 Low pressure test The low-pressure air test is suitable for old buildings because all the sanitary appliances have been installed. Disassembling these appliances for have pressure test is troublesome and costly It was found that the low-pressure air test is effective in locating the major leakage defects such as the workmanship defects by jetting bubble solution to the suspected defective points. But for minor defects such as the moulding defect it was difficult to locate the minor defects because the small 38mm w.g. air pressure is not strong enough to form soap bubble from the minor defective point. 5.3 Finding and Limitation Anti-siphon valve with metal disc provides rigidity and weight for better air seal. In regards to air-test during the course of construction, there are several measures in terms of practicality. One of the measures which require special attention is that the section of pipes which has been undergone air pressure test should be properly protected from being damaged. It is always advised to test the whole system at the pre-handover period. However, considering the height of building which could be more than 300 meters, it is advisable to test the system by sections. 6. Reference 1. The functions and installation of PVC drainage traps with an anti-siphon valve by

Chan Iat Keong, page 19, Journal of Hong Kong Engineer, June 2008 7. Presentation of Author

IK Chan is a member of CIPHE. His expertise is laboratory testing which are related to environmental hydraulic, heat and mass transfer and thermo-fluid. He presently is working in the Hong Kong Polytechnic University.

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Appendix 1

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Appendix 2

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Appendix 3 The weight of the anti-siphon valve disk, based on copper disc valve, was calculated as follows: Based on the copper anti-siphon valve under test M1=Mass of copper disc in grams M2 =Mass of guide rod in grams = 1.17g M3 = mass of sealing sheet in grams = 0.26g M=total mass of the anti-siphon valve=M1+M2+M3 d = diameter of valve seat = 13mm D = diameter of copper disc = 19mm g = gravitational acceleration = 9.81m/s2

At the time of valve opening, Mg=∆p*area of valve seat ∆p=Mg/area of valve seat

4/81.9*)1000/(

2dMp

π=∆ = 213*

4*1000*81.9*π

M (Pa or N/m2)

∆p=73.9M (Pa) But 10Pa = 1mm w.g. So that∆p (mmAq) = 7.39*M