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View the thread, titled "Long waste pipe run aav and or antivac trap" which is posted in UK Plumbers Forums on UK Plumbers Forums.

Matt0029

Gas Engineer
I have a long waste pipe run that is out side of the recommended distance of 4 meters for 50mm pipe. It only has one appliance on it. But because of the length of the run I want to stop self syphonage of the trap. Is there any benefit of fitting a trap with and anti vac adapter or anti vac built in. The a larger aav after the trap to allow more air in to help discharge? Or would they counteract each other? Thanks
 
A constant fall is vital it may help to equal out the pressure created and aid a quieter discharge and less gurgling , when you say appliance do you mean washing machine ? Dishwasher ? If the answer yes then surely a stand pipe is all that's needed as theres a air break ? What's you connecting to ?? . Kop
 
Unless you've got a bath discharging into the 50mm and lots of elbows in the run you'll struggle to get sufficient volume to create a large enough plug of water to create suction.
As K-O-P, steady fall and bends not elbows.
 
A constant fall is vital it may help to equal out the pressure created and aid a quieter discharge and less gurgling , when you say appliance do you mean washing machine ? Dishwasher ? If the answer yes then surely a stand pipe is all that's needed as theres a air break ? What's you connecting to ?? . Kop
Surely not? If there were siphonage, you'd siphon out the trap below the stand pipe allowing foul air to enter the building.

In any case, if you want to comply with the recommendations of ADH, then secondary vent, not AAV etc is the only way to go. But as ADH is a recommendation not a rule, if the pipe run is well designed then it may well be that the trap will not suffer from siphonage and that no device is required. I'd argue that if you tested the branch for trap siphonage and it passed, Part H will be satisfied even if ADH is not.
 
Thanks but would an aav installed after the trap aid discharge on and also protect the trap as good if not better then a anti vac trap. As will alway a greater volume of air in as the water discharges?
 
personally I would run the waste in 50mm add a tee with a cleaning eye the machine would discharge via a washing machine standpipe with a 75mm water seal, have a continuous fall to drain keep it simple as possible in this instance a air admittance valve is not necessary. Regards kop
 

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Matt0029

Gas Engineer
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Heating Engineer (Has GSR)

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Long waste pipe run aav and or antivac trap
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