Newly installed shower waste not draining

[CraigDiver]

Hi,

I have just installed a new shower enclosure. The 40mm waste drops 100mm below floor, travels 1.5m with 10mm drop, does a 90 degree bend, travels a further 1m to an in-line trap, travels a further 0.75m into stack. By the time it reaches stack it has a drop of around 50mm over the length. The shower panel is fed from a combi-boiler with lots of flow (possibly 11 ltr/min +). The waste originally had a plastic debris trap screwed underneath the chrome cover - with this in place the water was not draining quick enough. I have removed this and it is just managing to drain the water and no more. At the moment I have the chrome cover removed completely just leaving a hole so that it drains effectively.
The house is only a few years old so no problems with stack etc.

It appears to me that it is air-lock that is preventing the water to drain - should I allow air in by putting a vertical pipe from before the trap to act as a vent? (the trap is in the eaves of the house for easy access)

Any help / advice much appreciated

Regards

 

[Gasguru]

It appears the new shower is installed too low.

The total drop over the whole pipe run is below the minimum limit of 18mm per meter.

The first 1.5 should therefore be at least 30mm.

If the 90 degree bend is an elbow (and not a swept bend) this will not help.

You don't say what type of trap is used - if its a HepVo is it upside down?

Shower traps I use have the pipe exiting about 10mm underneath the tray - did the original pipe exit lower down?

Put a 75mm shower back trap on and sort out the fall - drop the stack connection if necessary (easier than moving the tray up).

 

[CraigDiver]

The plughole is 100mm above floor level, it goes down through floor and immediately through a 40mm 90 degree glued bend. travels 1.5m dropping 30mm, another 90 degree glued bend, travels a further 1m to trap which is just a U shape in-line (pipe run has dropped 50mm by this point). travels further 0.75m, another 90 degree bend then falls at about 30 degrees into stack.

The pipework cannot be moved as runs through joists - am I using the wrong type of trap?

Please helllpppppp!!!!

 

[CraigDiver]

With the plughole cover removed (so just left with a hole in shower base) the water drains ok - If i intentionally cover the plughole so the water backs up in the shower base then let go, it appears to have problems draining - like an air lock

 

[Gasguru]

Have you installed a new shower tray, or changed the pipework in any way. Did the old shower drain correctly. Have you increased the flow rate from the shower head? Perhaps the old shower had a lower flow and the waste just about managed. You could knock the flow-rate down.

Hope you are using a decent spirit level to measure the fall (and have checked its accuracy) - most short levels are totally inaccurate -especially the free one's given out by the mail order companies.

You now say the first 1.5 falls 30mm - before it was 10mm.

As I said the total run is below the minimum fall gradient required.

Are the bends knuckle or swept bends - knuckle bends will allow the increase friction and increase the chance of water backing up.

Get rid of the inline trap - if the flow rate is slow it will block easily and how are you going to clean it.

Normal shower traps are easily cleaned by removing center piece.

 

[CraigDiver]

I really appreciate you replying.

It is a totally new install, initially I just guessed the measurements.

The total pipe run is 3.75m dropping around 50mm in the first 3m and dropping a further 30mm in the last 0.75m into the stack

There is not trap directly under the shower base as it is completely inaccessible. I have therfore put the trap in the pipe run in the eaves which is very accessible. However the trap is some 2.5m from the shower base.

I cannot move raise / lower the shower base or install a trap under it - any suggestions - if i removed the in-line trap would i get a smell from the stack?

 

[Gasguru]

50mm / 3 =16.7mm per meter.

(50mm+30mm) / 3.75 = 21mm per meter.

The minimum standard as far as I'm aware is 18mm per meter with swept (longer radius) bends.

It no good having the first section with a gradient to shallow and expecting the last section to pull the water through.

If you have used too much solvent glue there may be a ridge at each joint causing further problems.

Even out the fall, install long radius bends, ditch the inline trap and it may then work.

Proper shower traps are accessible for cleaning from the grill side- you just remove the grill and center piece by twisting it out.

You must have a trap.