Water seal depth on shower waste

[mrhenry]

Hello, my understanding is that the water seal depth is supposed to be at least 50mm. I was about to use this mcalpine trap, but it only has a water seal of 25mm https://mcalpineplumbing.com/traps/...90cp10-53c-90mm-shallow-shower-trap-53mm-high

The reason I was going to use that one is not actually for it's shallow height but because the outlet pipe is high up, so I can get enough of a fall on the waste pipe. It's quite annoying that for all the other traps I've looked at, the outlet is coming out too low down to get the fall needed.

Can someone explain why mcalpine is making a trap that doesn't meet the required regulation for the water seal? What have I misunderstood?

 

[Madrab]

At the end of the day the manufacturers construct fittings to suit different needs but they don't manage how they are used. They don't make fittings to simply comply with the regs, that's down to the installer.

Just for clarity with a standard soil stack setup the requirements is for a75mm depth of seal. The 50mm min seal depth is where there is an existing dedicated waste run into an open outflow, say into a gulley or hopper, where there is little chance of the seal being pulled by other outlets.

There same issue is where a shallow bath trap is used, ideally to comply with the regs the same applies to the trap you link to is there should really be another deeper sealed trap installed before the waste enters the stack, like a running trap or waterless trap like a HEpvO or similar.

 

[mrhenry]

Interesting. I don't think I've seen any traps with more than a 50mm water seal, nearly all are 50mm. Perhaps this regulation is not adhered to very rigidly? I have just found this guide that says shower and bath is 50mm all others 75mm https://www.tradingdepot.co.uk/info...ng-products/mcalpine-installation-guidelines/

Would it be a bad idea to use the trap I listed with the 25mm water seal?

 

[Madrab]

I was looking at the the standard trap requirements into a stack for sinks/basin etc. but of course most standard bath traps all come with a 50mm seal so you are correct, 50mm is the min on baths and showers as they are slower draining, unless it's into a gulley/hopper and then it can be reduced to 38mm.

You do get 75mm seal shower/wet room traps, super high flow fitted a few, one is - https://mcalpineplumbing.com/wet-ro...r-seal-gully-horizontal-outlet-sheet-flooring

As far as using as trap with a 25mm seal. I've seen baths and showers use a shallow bath trap @ 19mm for years without issue. Is the shower waste run only for the shower and could it be increased to 50mm? That'll avoid the chance of self syphoning and you may get away with it.

 

[mrhenry]

It's on the same run as a bidet that never gets used. There's a bath and a sink on a perpendicular wall. I guess they go into the stack separately. Perhaps I should investigate the connection that end and see if it could be lower. The easiest option would have been to simply increase the height of the tray on the riser but unfortunately I've already put the tiles in. I'm not sure why I didn't check the fall before tiling but here we are.