32mm vent pipe?

[mike42]

I wonder if anyone might be able to tell me if this techflow top entry flange has a 1 inch female bsp connection the top or is it 3/4 inch?

I've searched all over the internet including the manufacturer site and the only place that decides to mention the connection is this ebay link that talks about 32mm ! I don't know what that is about.

The reason I ask is there is currently a 22mm feed out the top and I want to upgrade it to 28mm (pic below) because I'm adding a second shower pump (mira) and the instructions say use a 45 diagonal pipe as an air seperator and also seem to imply the pipe is 28mm. YOu can see we've currently got a near horizantal feed in 22mm.

https://www.ebay.co.uk/itm/Techflow...051781&hash=item54220bfca6:g:Uz4AAOSwHnFVskKe

 

[Hugh Jaleak]

Looks to me as there may be a 28x22mm reducer already in the top outlet, so the top outlet would be 1" female iron.

I'm more concerned about where that existing top connection goes to. If its the vent, and that is a lever valve in the picture, it needs removing!

 

[Gasguru]

If that's the Techflow flange then it may be plumbed incorrectly and certainly shouldn't have a lever valve on the top connection.
The shower pump should be on the side 22mm connection.

Toggle through the images and you can see the water pathways...

https://www.bellabathrooms.co.uk/stuart-top-entry-flange-by-stuart-turner.html

 

[mike42]

So, firstly let me deal with the safety issue noticed by Hugh. Slightly embarrassed to admit it was me that put it there as I was doing other work on the hot side (couple of months ago). I naively thought at the time that it would need someone to close the valve, the hot water to be on, and both stats to fail for it to be a real problem. Hugh has made me think that this is not just a contravention of building regs (I think) but actually could be dangerous when closed even if the boiler+cylinder stats work fine because the water in the tank may expand and there is nowhere for the steam to go - I'd be forcing a cylinder not designed to work at pressure to be pressurised. I'll be ripping it out (well moving it) as part of the work to add a second shower pump.

As for the outlets, that is a good image at bella (the first diagram you get to that is) and that is how I plumbed it (until I stupidly added that lever valve). I've added another pic below that should make that clear.

SO, after all that, the Mira design doesn't use a cylinder flange but a "natural" air separation that takes place by having the main feed from the HW at a 45 degree angle (not just slightly upwards as it is currently and as it shows in the Bella diagram). Then the shower pump feed is taken from a regular 90 tee off that pipe. Mira's schematic is below too.

What I would really like to know is if having two shower pumps like this likely to work ok? And also, maybe an easier question, if I'm doing this, is there benefit in me upgrading the existing outlet pipe to 28mm and removing that dog-leg on the existing hot feed feed (painted pipe on left) because below the dog-leg is already 28mm and seems odd the outlet is currently 22mm. (In other words the painted pipe is 22mm up to the vent but below that dogleg is already 28mm.)

Thanks for reading !

Mira Schematic:

 

[Hugh Jaleak]

No valve should ever be fitted on the open vent path of any system. It is there to allow steam and pressure to escape in the event of a stat failure and the cylinder boiling. Some pressure may be relieved via the cold feed, but I wouldn't want to see what happened, valve needs to be removed as soon as practical. If you want an additional isolation valve on the hot supply, fit it underneath the tee, so the open path to atmosphere is maintained.

Saw many showers fitted as an apprentice with the hot feed teed off the underside of the horizontal leg from the cylinder to the vent, main concern is to prevent air getting drawn into the pump which can cause cavitation and premature pump failure. Any pump warranty could also ne invalidated if the plumbing is found to be incorrect. Fitting a proprietary flange to the cylinder outlet should be sufficient to satisfy the pump manufacturers requirements I'd have thought.

I dont see 2 pumps being an issue, as long as if both are to be used simultaneously, the cold water supply to replenish the cylinder is up to the job. Bear in mind both hot and cold supplies are (usually) coming from the same cistern, and if you're taking this water faster than the cistern can refill, your shower(s) will soon run dry. Also 22mm supply to cylinder may not be adequate for 2 pumps. 28mm may be needed if it isn't already.

 

[mike42]

No valve should ever be fitted on the open vent path of any system. It is there to allow steam and pressure to escape in the event of a stat failure and the cylinder boiling. Some pressure may be relieved via the cold feed, but I wouldn't want to see what happened, valve needs to be removed as soon as practical. If you want an additional isolation valve on the hot supply, fit it underneath the tee, so the open path to atmosphere is maintained.

Saw many showers fitted as an apprentice with the hot feed teed off the underside of the horizontal leg from the cylinder to the vent, main concern is to prevent air getting drawn into the pump which can cause cavitation and premature pump failure. Any pump warranty could also ne invalidated if the plumbing is found to be incorrect. Fitting a proprietary flange to the cylinder outlet should be sufficient to satisfy the pump manufacturers requirements I'd have thought.

I dont see 2 pumps being an issue, as long as if both are to be used simultaneously, the cold water supply to replenish the cylinder is up to the job. Bear in mind both hot and cold supplies are (usually) coming from the same cistern, and if you're taking this water faster than the cistern can refill, your shower(s) will soon run dry. Also 22mm supply to cylinder may not be adequate for 2 pumps. 28mm may be needed if it isn't already.

That's all useful and interesting thanks Hugh. Regarding the flange, it seems Mira do not suggest a flange into the cylinder is needed since the diagram shows the draw off from a 45 angled pipe (which presumably is even better than horizontal) ? Not sure that arrangement is better than a side entry flange though. Still, I'm glad I think I don't need to fit one of those - it sounds a bit scary and knowing me we'd be out of hot water for a month if I attempted it !

If I do it the Mira way and use 28mm with a 22mm draw off to the pump I'll post here (years probably at my rate) when all the work is done and whether satisfactory.

P.S. I wonder if the reason Mira do it this way is something to do with I think their pump is a "pull" pump rather than a push. i.e. their pump (I think it said) is best suited close to the shower head whereas a lot of other pumps are sited close to the cylinder.

 

[Hugh Jaleak]

To be honest, I think the Mira diagram is slightly exaggerated, with the 45° outlet run from the cylinder, in all my time plumbing I have never seen one done like that. It should have a slight rise from the cylinder to the vent section yes, to allow air bubbles out, but 45° is somewhat drastic. Mira were printing that diagram 25 years ago, and bear in mind it is a guide.

A Surrey type flange should be more than adequate to supply a shower pump without air being an issue if fitted correctly. Essex flanges can also be used, but they are a beggar to fit and not for the faint hearted!

 

[mike42]

Thing is though there is already a top flange serving the existing pump - unless you're saying I could feed the second pump from there too without triggering the flow switch on the first? Otherwise I thought I'd try the Mira way for the second.

Many thanks indeed for bringing your experience to bare. I guess if nothing else, there normally isn't that much space in an airing cupboard for such a 45 degree pipe ! I imagine there are plenty of housewives who might not be overly happy to lose shelves above the tank!

 

[Hugh Jaleak]

Are you likely to be using both showers together? I worry, should you try to, even if shower supplies are taken from both outlets if the cold feed will replenish the cylinder fast enough to prevent air being drawn back down the vent pipe.

Secondly there is also the issue of your cold storage capacity, the standard cistern size is usually 40/25, so with a useable amount of around 25 gallons how long have you got until the supply runs dry? Mains supply is going to struggle to replenish the cistern at the rate you are using it.

 

[DavidLewis]

Can you not feed both showers from the one pump?

 

[mike42]

Can you not feed both showers from the one pump?

I must admit I hadn't really thought of that BUT it would be beneficial to have two pumps because the extra shower will go to an annex and we wouldn't want to here the pump every time anyone in the annex has a shower. And sadly, the new pump has already been bought and is integrated with the mixer that mira provide.

 

[mike42]

Just to say I've now done the work - at least prepared the pipework for the second shower feed as per the mira diagram above. Its now all 28mm from the tank as it was originally installed many decades ago (although the 45 degree vent is new). I've also removed the lever valve on the vent pipe! My soldering is as ugly as ever but at least it didn't leak (phew!!!)

Interestingly, as I was fitting the new pipework and had drained down a fair amount of water from the cylinder and had closed off the feed to that cylinder, after about 10 minutes the water started spilling out the top! I drained some more water out but couldn't understand where this water was coming from. I started worrying about a leak inside the cylinder from the ch system coil. However, I now think (well bloody hope!) that what was actually happening was expansion of the tank - exactly the kind of expansion that Hugh was worried about - but bare with me.

Whilst doing this work, I made the error of not turning off the ch system. In fact the HW was switched on and heating the cylinder. Now I'd only taken a few cupfulls from the tank and this vented tank is bigger than most (goes up to my neck and I'm about 6ft tall). Once I'd turned off the HW on the programmer, I ceased to have this problem of it spilling over every 10 minutes. Now had that water had nowhere to go, I'm not sure what would have happened - the weakest valve on the cylinder blown?

Anyway, if anyone has kindly read this far, I wonder if they might be able to advise on that ugly looking lever valve hanging off the new vent pipe? Its there like there because I intend soon to add the new pipe run for the new shower off it but as it stands how risky is it? I was careful to tighten it well but still worried it could blow off since its not supported?

 

[Nige F]

If the valve can't be rotated round the pipe by pushing on the lever ( keeping it shut ) then you're fine.

 

[Hugh Jaleak]

As Nige says, if it's done up properly it'll never come off. Otherwise every compression joint would be at risk of failing!

Was the cold supply to the cylinder shutting off totally when you were working on the system? I'd expect a certain amount of expansion if cylinder was being heated but it would be gradual, I have do wonder if the feed was letting by a little, and slowly allowing the level to rise, after you'd removed some water each time.

Lastly, if you're not over confident in soldering end feed fitting, spend a bit extra and get Yorkshire fittings. Can add a little solder yourself for belt and braces, but unless you are truly hopeless, they're very unlikely to leak.

 

[mike42]

Yes the cold water supply has a new lever valve on it and I've tested it so was definitely shut. Also when I turned off the central heating hot water off the water stopped bubbling over. It was like a very gradual oozing over the top. The tank is bigger than usual and is pretty fast to heat up.

Re end feeds - ha good point! I used to use Yorkshires and still do if in a really tight spot but not only do they cost a bit more they are also less available in all types (especially at the 28mm size). Maybe I should give up with endfeed but I am getting better (believe it or not !).

What I tend to do now is because I'm not confident especially if I can't see round the back is to just keep adding more and more solder till it drips. I do use a mirror at the back but not whilst I'm actually soldering so still not confident to know if the solder got sucked in. Of course they look ugly and I waste a lot of solder but at least I've not had one leak since I started doing that. I'm hoping that with practice I'll get more confident knowing when I've got a full ring so won't need any extra.