Shower waste trap and P bend

[AverageDIYerEssex]

ahh ok. I'll leave that idea alone then.

Yes all the new waste I bought was Aquaflow but the soil pipe and boss that is on there is Flomaster. I checked the boss adapter and does feel pretty snug but I did try some old flomaster fittings on the Aqua pipe and as you say there is definately a difference. I'll make sure to stick to one brand for the whole thing if I can.

 

[Madrab]

Yeah - it seems Aquaflow is the odd ball, for some reason TS have started to use it - I honestly think it's an attempt at them trying to force people to only use their fittings and pipe - every other waste pipe system is relatively interchangeable - Osma/Wavin/Flo/Poly/etc

 

[AverageDIYerEssex]

Ok so in an attempt to keep the run length down and thus achieving a better fall ratio, I'm now considering cutting across diagonally across the joists. This will also avoid having to move copper pipes further along that first joist void.

I have two potentially routes (depending if I can get away with an elongated hole for the straight across method)

Option 1 is using 45s to snake though the joists and option 2 is straight across. Need to run some tests on hole size and tolerances for my joists but what are your thoughts?

 

[Madrab]

Keep the number of bends of any type to a min, all it will do it create turbulence and slow the flow.

Hole sizes are key though as far as affecting the joists is concerned.

 

[AverageDIYerEssex]

Ok so been on the calculator. I think I can move the original joining elbow and boss down a little add 90mm to the overall fall.

I've done a sketch if you wouldn't mind double checking my theory and workings out.

I think I should be able to get 64mm/m.
The overall difference in heights (measured from the bottom of the fitting opening) is 217mm.
By going up, across diagonal through the joists with a 56mm ellipse hole with 40mm pipe at 45 degrees and then up again to the boss, total of 3.4m.

217/3.4=63.8mm/m

I then plan on putting the basin (32mm) teeing into the bath (40mm) that'll run a total length of 3.6m which will give it a 43mm/m fall.

Both going into separate bosses.

How am I doing so far? lol.

 

[Madrab]

Yes ok so far - though I'd work with a figure midway between the fall measurements, anything around 50mm/m will be more than enough, it'll allow for smooth drainage along the run and help it to self clean.

Use the extra height there is to drop the outlet from the shower trap down say 60mm on a 45deg, ideally within 100mm or closer of the trap's outlet, that will accelerate the waste water down into the run and allow the trap to evacuate quickly. That will maximise the flow from the trap and waste and avoid any backup into the tray. That should still allow for at least 50mm/m fall on the run

Do you know the flow figures of the shower and trap?

 

[AverageDIYerEssex]

Yes ok so far - though I'd work with a figure midway between the fall measurements, anything around 50mm/m will be more than enough, it'll allow for smooth drainage along the run and help it to self clean.

Use the extra height there is to drop the outlet from the shower trap down say 60mm on a 45deg, ideally within 100mm or closer of the trap's outlet, that will accelerate the waste water down into the run and allow the trap to evacuate quickly. That will maximise the flow from the trap and waste and avoid any backup into the tray. That should still allow for at least 50mm/m fall on the run

Do you know the flow figures of the shower and trap?

Thank you. I'll do some workings tomorrow and get that falling straight after the trap.

Ok so the shower head is a 300x300 square rainfall style with a 1/2" fitting (no output rating on website)

The mixer unit doesn't have anything other than minimum and maximum pressure (0.5-5 bar) but has 3/4"ins and outs

The shower tray and waste however states "Water flow capacity of up to 34 litres per minute"

Not sure if any of that helps.

 

[Madrab]

The figures are more to understand the the shower output against the trap flow figures, just ensures there's enough drainage for the possible shower flow but if the tray waste/trap will flow up to 34L/Min then the shower shouldn't come any where near that.

 

[AverageDIYerEssex]

So... another day on it. I reconfigured the boss and the toilet stack. Cut a load of floorboards and got into some tight spaces to take the stack apart to re do it a different way. Had to de-braise that copper pipe in the pic and move it the other side as it was in the way. I now plan on going into both sides of the boss instead of adding another.

I have dry fitted the bath run and have secured it and have a 50mm/m fall on it. This will take the bath and sink.

After closer inspection I am not going to be able to do the diagonal for the shower run because of pipes and too many existing holes in the joists where they would need to go.

Which leaves me with the zigzag run of 4.2m total and will give me a drop of 40mm/m with a 30mm initial drop out of the shower as you suggested. I would use 45's to take the sting out of the bends and I know the regs' 'max' run is 3m but what's your honest opinion on this? Obviously it's my own home not a customer, and this run will only have the shower on it so I'm not sure if the siphon will be an issue.

Flowplast website said they recommend either going up a size (which I'd ideally like to avoid as I have a stack of 40 here with fittings) or add an AAV. I never knew drainage was so complex.

 

[AverageDIYerEssex]

Just thinking... even if I did the whole shower pipe in 50mm pipe, would it actually make any difference as the shower trap outlet is only 40mm? Would it still be better than running 40mm pipe?

 

[Madrab]

You would probably be ok with swept bends as against 45's but if you have the 45's then no issue with that approach. 50mm waste run is just to stop the pipe from becoming overwhelmed and then it starts to cause a vacuum. Even if the outlet is 40mm it's all down to flow and capacities, the higher the flow the greater chancing of the waste pipe running fuller over longer distances and therefore pulling on the trap when it empties. I would think you would be OK with 40mm on the run given it's just the shower but of course the standards ask for 50mm.

Less chance of that happening with a shower of course as it has lower flow that say a bath or basin emptying all at once.

 

[AverageDIYerEssex]

So I went out today and bought 50mm just to be safe. Do you think I should whack an AAV on that line too or do you think the 50 will be ok?

I also bought sweeping bends instead of the 45s

 

[Madrab]

If it's just the shower then no it shouldn't need a vent