【正文】 transient will also be seen later in a discussion of the trap seal responses for the network. pressure levels within the network during the . discharge phase of the simulation. Note surcharge at base stack 1, pipe 1 at . It will also be seen, Fig. 6, that the predicted pressure at the base of pipes 1, 6 and 14, in the absence of surcharge, conform to that normally expected, namely a small positive back pressure as the entrained air is forced through the water curtain at the base of the stack and into the sewer. In the case of stack 4, pipe 19, the reversed airflow drawn into the stack demonstrates a pressure drop as it traverses the water curtain present at that stack base. The simulation allows the air pressure profiles up stack 1 to be modelled during,and following, the surcharge illustrated in Fig. 6. Fig. 7(a) and (b) illustrate the air pressure profiles in the stack from to s obsession with odour exclusion [2], [3] and [4], depend predominantly on passive solutions where reliance is placed on cross connections and vertical stacks vented to atmosphere [5] and [6]. This approach, while both proven and traditional, has inherent weaknesses, including the remoteness of the vent terminations [7], leading to delays in the arrival of relieving reflections, and the multiplicity of open roof level stack terminations inherent within plex buildings. The plexity of the vent system required also has significant cost and space implications [8]. The development of air admittance valves (AAVs) over the past two decades provides the designer with a means of alleviating negative transients generated as random appliance discharges contribute to the time dependent waterflow conditions within the system. AAVs represent an active control solution as they respond directly to the local pressure conditions, opening as pressure falls to allow a relief air inflow and hence limit the pressure excursions experienced by the appliance trap seal [9]. However, AAVs do not address the problems of positive air pressure transient propagation within building drainage and vent systems as a result of intermittent closure of the free airpath through the network or the arrival of positive transients generated remotely within the sewer system, possibly by some surcharge event downstream—including heavy rainfall in bined sewer applications. The development of variable volume containment attenuators [10] that are designed to absorb airflow driven by positive air pressure transients pletes the necessary device provision to allow active air pressure transient control and suppression to be introduced into the design of building drainage and vent systems, for both ‘standard’ buildings and those requiring particular attention to be paid to the security implications of multiple roof level open stack terminations. The positive air pressure attenuator (PAPA) consists of a variable volume bag that expands under the influence of a positive transient and therefore allows system airflows to attenuate gradually, therefore reducing the level of positive transients generated. Together with the use of AAVs the introduction of the PAPA device allows consideration of a fully sealed building drainage and vent system. Fig. 1 illustrates both AAV and PAPA devices, note that the waterless sheath trap acts as an AAV under negative line pressure.Fig. 1. Active air pressure transient suppression devices to control both positive and negative surges.Active air pressure transient suppression and control therefore allows for localized intervention to protect trap seals from both positive and negative pressure excursions. This has distinct advantages over the traditional passive approach. The time delay inherent in awaiting the return of a relieving reflection from a vent open to atmosphere is removed and the effect of the transient on all the other system traps passed during its propagation is avoided. basis for the simulation of transient propagation in multistack building drainage networks.The propagation of air pressure transients within building drainage and vent systems belongs to a well understood family of unsteady flow conditions defined by the St Venant equations of continuity and momentum, and solvable via a finite difference scheme utilizing the method of characteristics technique. Air pressure transient generation and propagation within the system as a result of air entrainment by the falling annular water in the system vertical stacks and the reflection and transmission of these transients at the system boundaries, including open terminations, connections to the sewer, appliance trap seals and both AAV and PAPA active control devices, may be simulated with proven accuracy. The simulation [11] provides local air pressure, velocity and wave speed information throughout a network at time and distance intervals as short as Transient propagation NomenclatureC+——characteristic equations c——wave speed, m/s D——branch or stack diameter, m f——friction factor, UK definition via Darcy Δh=4fLu2/2Dgg——acceleration due to gravity, m/s2 K——loss coefficient L——pipe length, m p——air pressure, N/m2 t——time, s u——mean air velocity, m/s x——distance, mγ——ratio specific heats Δh——head loss, m Δp——pressure difference, N/m2 Δt——time step, s Δx——internodal length, m ρ——density, kg/m3Article OutlineNomenclature 1. Introduction—air pressure transient control and suppression2. Mathematical basis for the simulation of transient propagation in multistack building drainage networks 3. Role of diversity in system operation 4. Simulation of the operation of a multistack sealed building drainage and vent system 5. Simulation sign conventions 6. Water discharge to the network 7. Surcharge at base of stack 1 8. Sewer imposed transients 9. Trap seal oscillation and retention 10. Conclusion—viability of a sealed building drainage and vent system pressure transients generated within