【正文】 building drainage and vent systems as a natural consequence of system operation may be responsible for trap seal depletion and cross contamination of habitable space [1]. Traditional modes of trap seal protection, based on the Victorian engineer39。s into the simulation. The air pressure in stack 4 demonstrates a pressure gradient patible with the reversed airflow mentioned above. The air pressure profile in stack 1 is typical for a stack carrying an annular water downflow and demonstrates the establishment of a positive backpressure due to the water curtain at the base of the stack. pressure profile in stacks 1 and 4 illustrating the pressure gradient driving the reversed airflow in pipe 19. The initial collapsed volume of the PAPA installed on pipe 13 was , with a fully expanded volume of 40l, however due to its small initial volume it may be regarded as collapsed during this phase of the simulation. 7. Surcharge at base of stack 1Fig. 6 indicates a surcharge at the base of stack 1, pipe 1 from to 3系統(tǒng)安全性提高、可靠性增加且設施和材料費減少，可見這種最初結果是令人高度鼓舞的，且足以證實潛在的明確利益，但進一步的模擬實驗有必要提供概念上的證明，且它與其他以檢驗為目的的實驗室、可能的地方、試驗相比是有利的。當吸氣閥直接反映本地壓力條件時，它們代表了一種控制活性氣壓的解決方法，它們自動打開，使新鮮空氣進入管道系統(tǒng)，從而使系統(tǒng)的壓力得到平衡并保護了冰封[9]。[1]水封保護的傳統(tǒng)模式，基于維多利亞女王時代的工程師對氣味排除的觀念[2]、[3]和[4]，通過交叉連接和立管排入大氣[5]和[6]，主要取決于信任基礎上的消極的解決方法。l volume. At that point the PAPA will pressurize and will assist the airflow out of the network via the stacks unaffected by the imposed positive sewer transient. Note that as the sewer transient is applied sequentially from stacks 1–4 this pattern is repeated. The volume of the high level PAPA, together with any others introduced into a more plex network, could be adapted to ensure that no system pressurization occurred. pressure profile in stack 1 and 2 during the sewer imposed transient in stack 2, 15s into the simulation. volume and AAV throughflow during simulation.The effect of sequential transients at each of the stacks is identifiable as the PAPA volume decreases between transients due to the entrained airflow maintained by the residual water flows in each stack. 9. Trap seal oscillation and retentionThe appliance traps connected to the network monitor and respond to the local branch air pressures. The model provides a simulation of trap seal deflection, as well as final retention. Fig. 11(a,b) present the trap seal oscillations for one trap on each of the stacks 1 and 2, respectively. As the air pressure falls in the network, the water column in the trap is displaced so that the appliance side water level falls. However, the system side level is governed by the level of the branch entry connection so that water is lost to the network. This effect is illustrated in both Fig. 11(a) and (b). Transient conditions in the network result in trap seal oscillation, however at the end of the event the trap seal will have lost water that can only be replenished by the next appliance usage. If the transient effects are severe than the trap may bee totally depleted allowing a potential cross contamination route from the network to habitable space. Fig. 11(a) and (b) illustrate the trap seal retention at the end of the imposed network transients..(a) Trap seal oscillation, trap 2. (b) Trap seal oscillation, trap 7.Fig. 11(a), representing the trap on pipe 2, illustrates the expected induced siphonage of trap seal water into the network as the stack pressure falls. The surcharge event in stack 1 interrupts this process at 2s. The trap oscillations abate following the cessation of water downflow in stack 1. The imposition of a sewer transient is apparent at 12s by the water surface level rising in the appliance side of the trap. A more severe transient could have resulted in ‘bubbling through’ at this stage if the trap system side water surface level fell to the lowest point of the Ubend. The trap seal oscillations for traps on pipes 7, Fig. 11(b) and 15, are identical to each other until the sequential imposition of sewer transients at 14 and 16s. Note that the surcharge in pipe 1 does not affect these traps as they are remote from the base of stack 1. The trap on pipe 20 displays an initial reduction in pressure due to the delay in applied water downflow. The sewer transient in pipe 19 affects this trap at around 18s. As a result of the pressure transients arriving at each trap during the simulation there will be a loss of trap seal water. This overall effect results in each trap displaying an individual water seal retention that depends entirely on the usage of the network. Trap 2 retains 32mm water seal while traps 7 and 15 retain 33mm. Trap 20 is reduced to 26mm water seal. Note that the traps on pipes 7 and 15 were exposed to the same levels of transient pressure despite the time difference in arrival of the sewer transients. Fig. 11(a) and (b) illustrate the oscillations of the trap seal column as a result of the solution of the trap seal boundary condition, Eq. (10), with the appropriate C+ characteristic. This boundary condition solution continually monitors the water loss from the trap and at the end of the event yields a trap seal retention value. In the example illustrated the initial trap seal values were taken as 50mm of water, mon for appliances such as .39。mm in the UK and other international standards dependent upon appliance type. Trap seal retention is therefore defined as a depth less than the initial value. Many standards, recognizing the transient nature of trap seal depletion and the opportunity that exists for recharge on appliance discharge allow 25% depletion. The boundary equation may also be determined by local conditions: the AAV opening and subsequent loss coefficient depends on the local line pressure prediction. Empirical data identifies the AAV opening pressure, its loss coefficient during opening and at the fully open condition. Appliance trap seal oscillation is treated as a boundary condition dependent on local pressure. Deflection of the trap seal to all