bath outlet discharging into hopper

[Mr W]

Hi

We've had our bath relocated, which means that we have a longer run of pipe where the outlet comes out of the wall, making its way about six feet, and an angle of 45degrees, to discharge into the hopper at the top of the drainpipe.

All tested ok when fitted by the plumber, but when he tested it was only a case of running the taps in the bath, and on that basis it's fine. Problem is, when a bath full of water discharges, the force of water coming out of the waste pipe splatters at great force against the inside of the hopper, spraying water everywhere.

Just wondering why this is happening - is the 45degree angle such that the water shoots at much faster than if the pipe was at a shallower angle? Or should the pipe have a right angle turn in it at the end so that the water exits vertically?

Mr W

[The Medway Handyman]

Probably both. Most bath wastes I see are at a shallower angle. A right angle bend on the end might help, or it might just cause the hopper to overflow more evenly.

[The Natural Philosopher]

The latter should work.

There is some justification for replacing the hopper with a proper junction.

[Andrew Gabriel]

Changing the shape/size/position of the spout could make a big difference. If the hopper has a 4" exit, I would direct the pipe end down that. (Could reduce to 32mm for that purpose.)

Changing the bath U-trap for one with an air admitance valve would help as it would draw air into the pipe, reducing the mass of water and the power of the jet at the end of the pipe.

Reducing the pipe to 32mm at the bath end might help by similarly restricting the flow. Doing it at the hopper end might not help but just produce more of a jet effect (unless directed down the outflow as mentioned above).

If the bath has a pop-up waste plug, adjust the plug so it doesn't open so far, again restricting the flow.

[Andy Hall]

Is that really true for this example though? I had always understood AAVs to be there to allow air in when the pipe is empty and there's a negative pressure further away from the appliance - purpose to avoid trap being sucked out.

In this case, wouldn't the pressure in the pipe be a little above surrounding atmosphere and therefore AAV wouldn't open?

Still it might work and nothing is lost by having one.

Another solution may be to fit an elbow at the hopper end to redirect the water inside that, or perhaps change the hopper to a different shaped one.

[Andrew Gabriel]

That's correct, and may also be useful here for that reason, but not the key point I was making in this case.

It's going to depend on the pipework, but generally where you've got a good smooth fall from the trap onwards as the OP seems to, you are supporting that column of water by a vacuum at that point, with the u-trap and plug grating being serious flow restrictions resulting in the negative pressure just at the point where the AAV is. If you look at an AAV, it generally opens all the time a full bath or basin is emptying (but even more at the end of course).

[Andy Hall]

Yes, now I think of it that way it seems right. Would it impact the result at the hopper though? I'm not sure about that.

[John]

I once fitted a 135 degree elbow at the end of a pipe to prevent this. Got the water directed better and stopped if bouncing off the far side of the hopper.

[HowieC]

Slow the speed at which the bath empties. Best way is to buy a few of those chrome-coated plastic hair-traps that just drop into the outlet.

Oh.. they also stop hairs getting into your hopper too!

(We use them all the time).

H.

[Mr W]

I'll have a go at this first, as seems the easiest, and see how it goes.

Mr W

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Mr W saying something like:

Yep, or a 45deg elbow to achieve the same end.