WC Waste

nph · 28 Apr 2007

Recently installed back to wall WC pan with push button dual flush. WC flushes OK but small solids come back into pan afterwards. Extra flushing (including bucket of water direct down pan) will not get rid. Waste pipe is 3" lead thro wall at 14 deg slope then 90 deg bend into 4" CI soil stack, total length of pipe is 640mm.

If I change the 3" to 4" PVC will this improve things or is there anything else I can try? Flush setting is OK, pan is level, holes in pan for flushing water OK, waste connection OK. Help please!!

Softus · 28 Apr 2007

I've not encountered 3" lead waste myself, but if that's the O.D. then the I.D. will be markedly reduced (because of the wall thickness).

Thinking about this, and ignoring the wall thickness for a moment, a 3" pipe has little more than half of the x-sectional area than the equivalent 4" pipe, and the ratio of wall surface to area is 33% greater, so the restriction to flow is, er, significant.

If you asked the pan manufacturer then I suspect they'd advocate using 110mm soil pipe, so maybe that's what you should be looking to do.

Nige F · 29 Apr 2007

you`ve not lived, then Softus.....or done work in a 1930`s refurbished Georgian mansion.........happy days

Softus · 29 Apr 2007

Nige F said:
you`ve not lived, then Softus.....or done work in a 1930`s refurbished Georgian mansion.........happy days

Certainly one or the other, but I'm not one to pretend that I've done what I haven't.

So, Nige, is my view of the restriction a practical one? Would you advice replacing the 3" section?

nph · 29 Apr 2007

Softus said:
I've not encountered 3" lead waste myself, but if that's the O.D. then the I.D. will be markedly reduced (because of the wall thickness).

Thinking about this, and ignoring the wall thickness for a moment, a 3" pipe has little more than half of the x-sectional area than the equivalent 4" pipe, and the ratio of wall surface to area is 33% greater, so the restriction to flow is, er, significant.

If you asked the pan manufacturer then I suspect they'd advocate using 110mm soil pipe, so maybe that's what you should be looking to do.

The wall thickness of the lead pipe is not much about 2mm I think but didn't measure it. The diameter of the WC pan outlet is even smaller so the 3" pipe should handle the flow which it did with the old WC before I changed it.

Nige F · 30 Apr 2007

dia. of wc outlet is smaller

........sounds like a foreign one , not a BS. one, and was the original Low Level with a flushpipe.........or close coupled.....seems most likely poor pan design........and I wouldn`t nesesarily change to 4 inch because we got the 3 inch ones to work OK........using a L/L cistern.....replacing an ancient syphonic

nph · 30 Apr 2007

Nige F said:
dia. of wc outlet is smaller ........sounds like a foreign one , not a BS. one, and was the original Low Level with a flushpipe.........or close coupled.....seems most likely poor pan design........and I wouldn`t nesesarily change to 4 inch because we got the 3 inch ones to work OK........using a L/L cistern.....replacing an ancient syphonic

Original was a low level with flush pipe. New pan is made by Stafford Ceramics who cannot be bothered to answer my emails. Identical pan fitted in downstairs cloakroom which initially suffered same problem but once pan connector changed from swan neck with extension (from pan to swan neck) to 90 deg connector it was OK. Waste outlet however, is 110mm dia in floor of cloakroom.

nph · 8 May 2007

Have now changed waste pipe to 110mm OD UPVC pipe but has made no difference. Old pipe was actually nearer 3.5" (90-95mm OD). Any suggestions as to what else I can try?

nph said:
Softus said:

I've not encountered 3" lead waste myself, but if that's the O.D. then the I.D. will be markedly reduced (because of the wall thickness).

Thinking about this, and ignoring the wall thickness for a moment, a 3" pipe has little more than half of the x-sectional area than the equivalent 4" pipe, and the ratio of wall surface to area is 33% greater, so the restriction to flow is, er, significant.

If you asked the pan manufacturer then I suspect they'd advocate using 110mm soil pipe, so maybe that's what you should be looking to do.

Click to expand...

The wall thickness of the lead pipe is not much about 2mm I think but didn't measure it. The diameter of the WC pan outlet is even smaller so the 3" pipe should handle the flow which it did with the old WC before I changed it.

Nige F · 8 May 2007

Ah so, Slafford Celamics on the banks of the Yangtsee

Crose Cloupled now? tly rising level of water in clistern until overflowing is within 10cm.

nph · 9 May 2007

Nige F said:
Ah so, Slafford Celamics on the banks of the Yangtsee Crose Cloupled now? tly rising level of water in clistern until overflowing is within 10cm.

Thanks for reply but already tried that and makes no difference. PS think you mean 10mm not 10cm!

Nige F · 9 May 2007

ah.......so

disrexic too

diynot

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