Abstract
In Japan, the following is legally defined: The depth of sealed water in a drain trap must be between 5 and 10cm. The construction of a vent pipe must be made in such a way that the difference between the pressure in a drain pipe working for the sealed water in a drain trap and the atmospheric pressure does not exceed over 25mm of the water column. However, the water seal phenomenon in a drain trap cannot be clarified in a static manner as mentioned above. It should be considered as an unsteady phenomenon being accompanied with the vibrating movement of a water column caused by an external force (or negative pressure). From the above mentioned viewpoint, the authors performed fundamental experiments and simulations with a computer in order to analyze the dynamic characteristics of water movement in a drain trap. Considerations are developed in the following order in this study to analyze the problem. 1) After free vibration experiments are performed with models, a numerical model Eq. (2') is built and the parameters are identified. 2) The assumed parameters found above are employed in impulse response simulation and agreement with the experimental values is confirmed. 3) Simulation when an arbitrary input (negative pressure) is applied is performed and agreement with the experiment values is confirmed. 4) Practical use of the above numerical model and the propriety of the assumed values of the parameters obtained by parameter identification are clarified by the above operation. The following conclusions have been made as a result of the study based on the above. 1) Simulation was performed and parameter identification was completed on four kinds of experiments on 11/4 in and 4 in traps using a numerical model. Moreover, the propriety of the assumed numerical model and its practical use at sufficient accuracy were clarified. 2) To be precise, this experiments may have to be expressed as the time variant system, that is, each parameters are functions of time. But it was clear that there is no obstruction to practical use as that parameters are unrelate to time by various examples in this report. This is nothing but that we have performed parameter sensitivity analysis. 3) The period over which a negative pressure is applied to the trap poses a problem, and it is clear that there is the possibility of the water column abruptly rising to 7cm, 10cm, etc. even when a negative pressure as small as 2cmAq is applied. Generalizing the above, it should be emphasized that the water seal phenomena in a drain trap is not static, but must be grasped dynamically.
