Test Method of Trap Performance for Induced Siphonage

Transcription

1 VII.4 Test Method of Trap Performance for Induced Siphonage K. Sakaue (1), H. Kuriyama (2), H. Iizuka (3), M. Kamata (4) (1) isc.meiji.ac.jp School of Science and Technology, Meiji University, Japan Nikken Sekkei Ltd., Japan (3) Nikken Sekkei Ltd., Japan (4) Faculty of Engineering, Kanagawa University, Japan Abstract The drainage system is designed in such a way that drain traps are not prone to seal break. Seal break is caused by seal loss phenomena, and induced siphonage plays an important role. A reliable drainage system cannot be designed without first defining trap performance for induced siphonage. However, no effective methods have been established to test the performance of traps. Based on the premise that seal loss phenomena are produced as response of seal water to pneumatic pressure in drain, we conducted free vibration test, single sine wave response test, and 2 times natural frequency response test using a pressure generating device with two types each of fixture traps, floor drain traps, and WC to elucidate their characteristics and strengths. The results clearly indicated that methods defining minimum pressure required to cause seal break was most appropriate for testing traps performance to withstand pneumatic pressure. It was also found that natural 47

2 frequencies obtained by the free vibration test, and max. response magnifications by the single sine wave response test were relevant and applicable. Keywords Drainage system, trap, induced siphonage, test method, single sine wave 1. Introduction The first consideration in designing any drainage system including vent system is to make it in such a way that it does not cause seal break. So-called seal break phenomena include such conditions as induced siphonage, self-siphonage, and evaporation. Of these, however, one that is pertinent to the entire system would be induced siphonage, which is characterized by seal loss caused by pneumatic pressure (referred to as pressure below) affecting the trap seal. In other words, induced siphonage is a dynamic vibrational response phenomenon caused by the flow of water in the drainage pipe. To prevent seal break caused by this induced siphonage, it is necessary to establish a way to predict pressure resulting from discharge load and entire system configuration such as piping, pipe diameter, type of vent system, as well as to clarify anti-pressure performance of trap (referred to as trap performance below). Theoretically it can be achieved by establishing permissible pressure based on trap performance, and by defining permissible flow rate against it for each system type. The more clearly we define the performance of each trap, the more flexibly we can design the section of piping in which the trap is placed. In the current designing scheme, trap performance is only defined by minimum seal depth with no pressure prediction made, and at the very best rough permissible flow rate for each system type is defined. Of all plumbing codes in the world, only the former DIN1986 in Germany and SHASE-S-218 in Japan stipulate permissible seal loss. As for permissible residual seal depth, only SHASE-S-218 has stipulations. In the ever-evolving world of plumbing system, designing of drainage system, extremely ill-defined compared to that of water supply system and hot water supply system, has been unable to respond to the trend of rationalization. Though the selfsealing traps without requiring seal water have been developed in Great Britain, water seal trap is still the mainstream in the world. It seems imperative that we clearly define trap performance to improve designing methods of drainage system. Based on the above considerations, the authors have tested various methods of defining trap performance [1-4]. In this study, as continuation of the ongoing research, the authors have examined testing methods using a simple device generating single sine waves with two types each of fixture traps, floor drain traps, and WC. 48

3 2. Experimental apparatus and measuring equipment 2.1 Experimental apparatus The experimental apparatus used in this study consists of a pressure generator (pistons, a frequency variable device, various chambers), drainage pipes, and an analyzer (Figure 1). It has a triple-piston structure with cranks adjustable at 8 steps between 15 ~ 5mm in increments of 5mm. Frequencies are variable in increments of.33hz within the range of.166 ~ 4.5Hz. It is also equipped with a small blower as a bias pressure device, which reproduces the steady pressure component. Amplitudes were adjusted by changing the water contents of vertical cylindrical chamber and pressure adjustment chambers, which in turn changed air volume in the chambers. Only one of the three pistons on the apparatus was operated this experiment. 2.2 Test traps Basic configuration parameters and cross sectional shapes of test traps are shown in Table 1 and Figure 2. The and for fixtures, the bell trap and contrary bell trap for floor drains are made of transparent resin, and seal conditions inside can be observed from outside (Figure 2). Actual models of two types of WC, supper water saving WC (WC -6L ) and water saving WC (WC -8L ) were used. 49

4 2.3 Measuring equipment We used a diffuse semiconductor type pressure sensor for measuring pressure, and a capacitive water level sensor for seal water level. The water level sensor had been modified so that it could be inserted into the inlet leg of a trap. Both of them had adequate response frequency of more than about 1kHz ; Changing device of frequency 2; Blower for bias pressure device 3; Chamber with piston 4; Pressure control valve 5; Mixing chamber 6; Pressure control chamber 7; Test trap 8; Water level sensor 9; Amplifier 1; Pressure sensor 11; Amplifier 12; Data roger 13; PC Figure 1 - Test apparatus 41

5 Table 1 Basic parameters of test raps Test traps Volume of seal Seal depth Ratio of leg s sectional area F 1) [-] For Fixtures For floor drains Contrary trap bell WC WC -6L WC -8L 2,47 1, ) - 2) Note 1) F = (mean sectional area of inlet leg) / (mean sectional area of outlet leg) of a trap 2) These weren't confirmed because an internal form was complex Contrary bell trap Figure 2 - Test traps 3. Free vibration test 3.1 Purpose Natural frequency and damping ratio are the two main basic response characteristics in forced vibration phenomena. Having damping ratio of.4 ~.6, seal fluctuation is known to cause weak damping oscillation [5, 6]. Considering the effects on trap performance, we used only natural frequencies as a parameter. Though there are several 411

6 methods of measuring natural frequencies, we adopted a method based on power spectrum of response of water level in this study. 3.2 Experimental method We first caused half-full seal to free-vibrate, and measured free-vibration wave patterns of seal. Then we obtained the density distribution of power spectrum of response of water level by giving FFT treatment to the wave patterns. The frequency at which the power spectrum density became maximum value was determined to be the natural frequency f. 3.3 Results and discussion As shown in Figure 3, power spectrum density distributions of each test trap were as follows: : 1.95Hz, : 1.93Hz, : 2.43Hz, Contrary bell trap: 2.57Hz. These values corresponded with the values obtained from the calculate equation of natural frequency. Although the density distribution of WC generally forms two peaks as that of WC -6L [7], the second predominant frequency of WC -8L was extremely low forming only one peak. If the most predominant frequency is regarded as natural frequency, the peaks of density distribution for WC -6L and WC -8L were 1.61Hz and 1.46Hz respectively. From this, the range of natural frequencies when test traps were half-full was found to be to be 1.4 ~ 2.6Hz. Power spectrum Power spectrum F : 195Hz F 193H F : 243Hz Contrary F : 243Hz WC 6L F : WC 8L F : Figure 3 - Power spectrum of water level and natural frequency f 412

7 4. Single sine wave response test 4.1 Purpose This experiment was intended to define trap performance by obtaining response characteristics (maximum response magnification) when frequencies of sine wave pneumatic pressure were fluctuated with its amplitudes kept constant. 4.2 Experimental method Single sine waves mainly consisting of atmospheric pressure with various frequencies and constant amplitude were applied to half-full seal. Then the response magnification curve as a function of frequency was obtained by based on calculation of the static seal level (X) of trap seal and the ratios of response fluctuations (X t ) against single sine wave pressure (response magnification M=X t /X) at each frequency were obtained. 4.3 Results and discussion Response magnification curves for each test trap are shown in Figure 4. Response magnification curves corresponded with density distribution curves in the free vibration test, and frequencies at which response magnification M reached maximum roughly corresponded with natural frequency f. However, with WC -8L, response magnification comparable to natural frequency f was noted at the second predominant frequency (2.4Hz) Vibration characteristics of test trap seal seemed to manifest more evidently in the single sine wave response experiment than in the free vibration experiment. Experimental method is simpler with only single sine waves of constant amplitudes used. As a result an experimental apparatus is not required to generate a wide range of pressure load, and the experimental apparatus itself can be reduced to small size. Response Response M = 4.8 (1.9 Hz) M = 5. (2. Hz) ifi ti M ifi ti M Contrary bell trap WC 6L WC 8L Figure 4 - Response magnification M of test raps 413

8 Vibration characteristics of test trap seal seemed to manifest more evidently in the single sine wave response experiment than in the free vibration experiment. Experimental method is simpler with only single sine waves of constant amplitudes used. As a result an experimental apparatus is not required to generate a wide range of pressure load, and the experimental apparatus itself can be reduced to small size. 5. Seal break test 5.1 Purpose This experiment is intended to define trap performance by measuring amplitudes at the time of instantaneous seal break when frequencies and amplitudes of single sine waves are changed. Instantaneous seal break refers to the conditions when air bubbles pass through top dip of trap. 5.2 Experimental method Single sine waves consisting of amplitudes of atmospheric pressure with a constant frequency were applied to half-full seal, and the minimum amplitude leading to instantaneous seal break within 1 seconds (referred to as seal break pressure) at the given frequency was measured. Then the seal break characteristics curve was obtained as a function of frequency and seal break pressure. 5.3 Results and discussion Seal break characteristics curves (seal break pressure curves) for each test trap are shown in Figure 5. The seal break characteristics curves roughly corresponded with density distribution curves obtained from the free vibration test and response magnification curves from single sine wave response test. The frequency where seal break pressure was minimum also corresponded with the natural frequency f. However, the minimum value of seal break pressure was extremely small in WC. The reason for this seems to be that WC was made of opaque ceramic, and that instantaneous seal break was not detected accurately as the conditions of seal could not be observed directly. Based on dynamic oscillation, seal break test is geared to focus on seal break, the most important element in this study, and seal break pressure provides convenient data to evaluate trap performance. However, as mentioned above, seal break test has a drawback in that instantaneous seal break cannot be detected accurately if traps are made of opaque materials. 414

9 Seal break pressure [Pa] 6. 2 times natural frequency response test 6.1 Purpose In the field of oscillation technology, frequency 2 times the natural frequency f of experimental subject has been used as eigenvalue of force. This experiment is P s min.= 196 Pa P s min.= P s min.= 216 Pa Contrary bell trap P s min.= WC 6L P s min.= 183 Pa WC 8L P s min.= Pa -8 P s min : Minimum seal break pressure 24 Pa 152 Pa Figure 5 Seal break curve of test raps intended to define trap performance by studying response levels of seal to single sine wave with 2 times natural frequency f. 6.2 Experimental method Single sine waves mainly consisting of atmospheric pressure with various amplitudes and constant frequency were applied to half-full seal for 3 seconds, and seal fluctuations and seal loss H loss were measured. Pressure waves with natural frequency f and 2 times f were applied. 6.3 Results and discussion The relationship between applied pressure and maximum seal fluctuation for each trap is shown in Figure 6. The input pressures (pressures waves inputted into the pressure generator) were retained at a constant level until the amplitude of applied pressure reached approximately ±15Pa, but the larger the amplitude, the more differences in output pressures (pressures actually measured in the pipe of test apparatus) were actually measured in traps (Table 2, Table 3). This phenomenon seems to have more to do with seal volume than with the size of cross-sectional areas of trap legs. It can be assumed that input pressure was lessened by resonance phenomenon when frequency f is applied, but on the other hand, air inside the apparatus became compressed before 415

10 applied pressure had any influence on seal fluctuation as seal volume increased when 2 times f frequency was applied. As far as seal loss is concerned, no evaluation of trap performance was possible as seal loss remained zero regardless of amplitude of applied pressure at 2 times f frequency (Figure 7). The experiment using 2 times natural frequency f proved to be unproductive as it required cumbersome procedures and considerable time, and it was difficult to adjust amplitude of applied pressure because of compression of air inside the apparatus. It was also found difficult to obtain clear indices by which performance of each trap can be evaluated and ranked WC 6L Maximum seal water level [mm] Pressure [Pa] Contrary bell trap Pressure [Pa] -5-5 Pressure [Pa] WC 8L -1-1 Figure 6 Relations ship between Pressure and max. water level of test raps 416

11 Table 2 Input pressure and output pressure (f ) Input pressure [Pa] Test traps Output pressure [Pa] Contrary tarp bell WC -6L WC -8L Table 3 Input pressure and output pressure ( 2 f ) Input pressure [Pa] Test traps Output pressure [Pa] Contrary tarp bell WC -6L WC -8L

12 Seal loss [mm] Pressure [Pa] -4 f 2 f -6 Figure 7 An example of output pressure against input pressure (f, 2 f ) Seal loss [mm] Pressure [Pa] -4 f 2 f Conclusion 2 times natural frequency response test was found inappropriate for testing trap performance. Considering the ease of experimental method and the size of experimental apparatus, minimum seal break pressures obtained by the seal break test seems to provide most appropriate criteria for evaluating trap performance. In addition, it is desirable to include natural frequencies and maximum response magnifications obtained by the free vibration test and the single sine wave response test respectively. An issue that needs to be addressed in the future is how to apply the seal break test to opaque traps. One way to achieve this would be not to judge instantaneous seal break by visually, but to use a water level indicator, and regard seal break as having occurred when water level reaches near seal depth mm when pressure is applied. In this study performance evaluation was only made in terms of negative pressure, where seal break is most likely to occur, as we used amplitudes of pressure waves based on atmospheric pressure. Therefore it is necessary to develop a method of performance evaluation in terms of positive pressure by applying bias inside the apparatus. 418

13 8. References 1. Sakaue, K., Kamata,M., Kuroda, K., Wang Y. (21). Studies on Dynamic Characteristics of Trap Seal, Proceedings of CIB W62 International Symposium (pp. E ) 2. Sakaue, K., Kamata, M., Zyang, Y. (27). A study on the Test method of Trap performance, Proceedings of CIB W62 International Symposium (pp ) 3. Kuriyama H., Sakaue, K., Yanagisawa, Y., Kamata, M., Sudo, H. (26), Studies on the Test method of Trap performance (Part 11), Technical papers of Annual meeting, SHASE (pp ). 4. Kuriyama, H., Sakaue, K., Yanagisawa Y., Kamata, M., Iizuka, H. (28). A study on the Test method of Trap performance using Simple Test Apparatus, Proceedings of CIB W62 International Symposium (pp ) 5. Sakaue, K., Shinohara, T., Kaizuka, M. (1977). A Study on the Dynamic Characteristics of the Trap Seal, Proceedings of CIB W62 International Symposium. 6. Sakaue, K., Shinohara, T., Kaizuka, M. (1982). A Study on the Dynamic Characteristics of the Seal in Deformed Traps, Proceedings of CIB W62 International Symposium. 7. Tomonari, H., Wang, Y., Kamata, M., Sakaue, K. (22). Numerical Studies of Seal Movement in Traps, Transactions of SHASE (pp.87-96) 419