Tp7 akavent systems principles(dr)

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Tp7 akavent systems principles(dr)

  1. 1. Akavent waste water drainage systems: Balancing the pressures Marc Buitenhuis Hydraulic research engineer Akatherm International BV, Panningen, The Netherlands 30-03-2009AbstractIn this article the principles of the Akavent waste water drainage systems will be presented.Balancing the pressures in the system and keeping them close to atmospheric is the main issuefor these systems in order to keep the water traps of sanitary devices in place. An open path tothe environment must be present for all the air in the system to avoid pressure surges and thusblow outs of siphons. To achieve this special fittings are used on every level of the buildingwhere branches enter the stack. 1. Introduction level within acceptable limits.A lot of waste water is produced daily bytoilets, bath tubs and showers,dishwashers, washing machines, etc. It allhas to be drained from the buildings andtransported to the sewage facilities.If a single drainage pipe would be usedthat is just capable of draining themaximum amount of waste water, largepressure peaks would result, sucking dry orblowing out all water traps, giving accessfor bad odors to enter the living spaces.In order to keep the pressure fluctuationslow the system has to be ventilated. Anadditional ventilation stack can do the job, Figure 1 Schematic of an Akavent stack systembut is a more complicated construction,costing considerably more, and takes up 2. Akavent systemmore valuable space in building shafts. Theanswer is a system using special devices, When fluid is transported in a pipe systemcalled Akavents at Akatherm, and a larger at a low discharge rate relative to thepipe diameter of 110 or 160mm. maximum discharge rate of the pipeThe principle of this system is based on system a so called annular flow will occurkeeping a free path for air to leave or enter in the vertical pipes. This means that thethe system, thereby keeping the pressure water will flow along the walls in an Pagina 1 van 3
  2. 2. annulus independent of the initial inflow Akavent collects the water in a chamberconditions. [1] before it drops down and flows inIn the center of the pipe a core of air will vertically to the main stream. The air in aoccur. If the vertical stack sticks through branch connects with the core of air in thethe roof and is open the core of air will stack through a ventilation hole [2].always remain at approximately the The main vertical water stream isatmospheric pressure. decelerated by the deflection in the bendThis in contrast to a plug flow that can [3] of the Akavent. This prevents break upblock the air path at any location in the of the annular flow and creation of apipe system. In front of the plug of water harmful plug flow.that cuts off the open air path a pressurepeak will occur, whereas a wake with a At the bottom of the vertical stack the flowvacuum behind the plug will be present. is channeled horizontally. The system hasThe pressure peak in the front will also to maintain ventilated through this bendenter the side branches and possibly blow also. Directly after this bend there is a riskout the water traps. When the water traps the system will be blocked by the hydraulicare able to withstand the pressure peaks jump that will occur because of thethey are threatened a moment later by the deceleration of the water in the corner.vacuum of the wake that can suck them This threat can be alleviated bydry. Both will lead to an open path for constructing a short ventilation stack fromsmelly sewer gases to enter the building. just before the bend to a location in theTo keep the water traps in place the horizontal pipe behind the hydraulic jumppressure has to be kept at approximately as shown in Figure 3.atmospheric level in the side branches also.To manage this the air in the branches haveto be in contact with the air core of thestack at all times. This is where the specialfitting, the Akavent, is brought into play 2 3 Figure 3 Ventilation construction in the change 1 from vertical to horizontal pipe. 3. Conclusions The Akavent waste water drainage system is all about keeping the air pressure in theFigure 2 Akavent system near atmospheric in order to keep the water traps in place. For this purpose aIn the branches the air is located at the large stack diameter (Ø110mm orupper half of the horizontal pipe (gravity Ø160mm) and special fittings, “Akavents”,driven separated flow). If the horizontal must be chosen as well as a specialbranch is plugged straight into the stack the precaution at the bend at the bottom towater would jet in with sufficient force to prevent the hydraulic jump from blockingdisrupt the core of air and thus disturbing the ventilation of the system.the pressure balance in the system. The Pagina 2 van 3
  3. 3. 4. References1. Robert W. Fox, Alan T. McDonald, Introduction to fluid mechanics, third edition, 1985, School of Mechanical Engineering Purdue University, John Wiley & Sons2. Arthur, Scott, Swaffield, John A., Siphonic roof drainage: current understanding, 2001, Water research group, Department of civil and offshore engineering, Heriot-Watt University, Edinburg, Scotland (UK)3. Swaffield, John A., Wise, A.F.E., Water Sanitary and Waste Services for Buildings, May 19954. Swaffield, John A., Galowin, L.S., The engineered design of building drainage systems, Oct 1992, Ashgate Publishing Company Pagina 3 van 3
  4. 4. 4. References1. Robert W. Fox, Alan T. McDonald, Introduction to fluid mechanics, third edition, 1985, School of Mechanical Engineering Purdue University, John Wiley & Sons2. Arthur, Scott, Swaffield, John A., Siphonic roof drainage: current understanding, 2001, Water research group, Department of civil and offshore engineering, Heriot-Watt University, Edinburg, Scotland (UK)3. Swaffield, John A., Wise, A.F.E., Water Sanitary and Waste Services for Buildings, May 19954. Swaffield, John A., Galowin, L.S., The engineered design of building drainage systems, Oct 1992, Ashgate Publishing Company Pagina 3 van 3
  5. 5. 4. References1. Robert W. Fox, Alan T. McDonald, Introduction to fluid mechanics, third edition, 1985, School of Mechanical Engineering Purdue University, John Wiley & Sons2. Arthur, Scott, Swaffield, John A., Siphonic roof drainage: current understanding, 2001, Water research group, Department of civil and offshore engineering, Heriot-Watt University, Edinburg, Scotland (UK)3. Swaffield, John A., Wise, A.F.E., Water Sanitary and Waste Services for Buildings, May 19954. Swaffield, John A., Galowin, L.S., The engineered design of building drainage systems, Oct 1992, Ashgate Publishing Company Pagina 3 van 3

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