15mm feed to 1 inch shower valve (and related questions)

[PASUK]

Hi everyone
Sorry first of all for what might seem like basic questions. Some context first then a few questions at the end...

I am fitting thermostatic shower valve/mixer (link to product) recessed into the wall.

Instructions specify that the ideal pressure is: 0.2Mpa-0.5Mpa
They also state 'standard' pressure: Dynamic water pressure 0.3+-0.02Mpa

My house...
Very standard gravity fed system.
1st floor (which is the top floor) has a hot water cylinder and the same floor the shower will be installed.
Loft has the cold water tank.
I have a Stuart Turner shower pump part number 44419 (link to product and specs etc) to be installed on the first floor, same as the shower and below the water tank which as mentioned is in the loft.
The specs say 1.5bar (0.15Mpa) but of course it depend on the head pressure or other factors which if I am totally honest I really struggle to understand how to figure out the pressure performance curves for pumps.
What I do know is that I already use this pump elsewhere in the house on the same floor and the pressure is very good. The pump uses 15mm pipes in and out for hot and cold. The only difference with this other shower is that its a little further away which needs the pipes to go up into the loft and drop into the other bathroom other side of the house.

Question 1: can someone first please help double check my measurements:

The shower valve seems to take a 1 inch type feed in for hot and cold.
I seem to struggle to find connections 15mm to 1" which in itself might be telling me something!

See image:

I'm struggling to figure out the connection size for the exit connections (image below) to the shower head and shower hose. Looks larger than 3/4inch but maybe I am not looking at this correctly. can someone help please?

Question 2: Can I feed feed this with 15mm given that the other shower with the same pump fed with 15mm works ok?

Question 3: Can anyone provide a link to a part at SF or TS for fittings that will allow me to use 15mm?

Thank you

 

[terryplumb]

The inlets are 3/4 inch BSP thread ,and the outlets 1/2 inch BSP thread.
15 mm supply's from the pump are fine.

 

[oldbuffer]

1. In theory your shower pump is a little underpowered for the new shower. In practice it will probably be fine.
2. The inlet thread is most likely 3/4" BSP. The outside diameter of a 3/4 BSP male thread is 1/04"
3. You need a male 3/4" to 15mm compression male "iron" (they are made of brass). Screwfix 82086
4. If the face of the inlet hole is flat, then a fibre washer between the 3/4" BSP of the iron and the face may provide an adequate seal.
5. If it were me I'd be using Flomasta pipe seal (Screwfix 4373J) on the threads to guarantee a seal.

 

[Madrab]

+1 for the reducer you'll, invariably they are 3/4" so a 15mm to 3/4" coupler and some thread tape/cord/liquid.

Don't understand your pressure figures though. Under the specs on that page for that Milano shower, their recommended pressure is 1Bar @ 17L/Min. Nothing in the install docs mentions anything about MPa?? Are the docs supplied different?

 

[PASUK]

Hi thanks.

Don't understand your pressure figures though. Under the specs on that page for that Milano shower, their recommended pressure is 1Bar @ 17L/Min. Nothing in the install docs mentions anything about MPa?? Are the docs supplied different?

Hi the paperwork included in the box had the following details, which initially threw me off compared to what I read before I bought on the website.

 

[PASUK]

4. If the face of the inlet hole is flat, then a fibre washer between the 3/4" BSP of the iron and the face may provide an adequate seal.

Thanks for the advice.

Looking at the face on the inside of the inlet I would say no washer?

 

[terryplumb]

Thanks for the advice.

Looking at the face on the inside of the inlet I would say no washer?

View attachment 255510

You would be correct.

 

[Madrab]

OK, so those figures will be optimal and it's preferred dynamic (sustained) pressure is 3 bar. That'll be for best performance.

You will struggle with your Hot and Cold water system as it currently stands I'm afraid to say. You will get a shower, it just wont be performing any where near it's best. As long as your prepared for that.

Going with the on site recommendations and specs I would suggest you would be well within your rights to return it as 'not as advertised' if you so wished.

 

[PASUK]

OK, so those figures will be optimal and it's preferred dynamic (sustained) pressure is 3 bar. That'll be for best performance.

You will struggle with your Hot and Cold water system as it currently stands I'm afraid to say. You will get a shower, it just wont be performing any where near it's best. As long as your prepared for that.

Going with the on site recommendations and specs I would suggest you would be well within your rights to return it as 'not as advertised' if you so wished.

Oh no! So i've made the silly mistake of already carving out the wall and chasing for pipes for these valves before finding this out! to make things worse it was a particularly thin wall and took me ages to get it all right without compromising the overall integrity of the wall. I didn't have space to build out a false wall to do this work.

Thinking of workarounds, would I be able to upgrade the pump? if so would you/anyone be able to recommend a good one that gives the right pressure?
If it helps to know I believe I am in a negative head situation as the shower head is only ~30cm lower than the bottom of the cold tank (certainly not more then 60cm as I think is the standard threshold between - and + head)

 

[Madrab]

If we are going by the shower MI's then your current pump is underpowered. As suggested, it will run the shower, it just won't run the shower as well as the shower can be run, if you see what I mean. So it depends on whether you will be happy with the output once it's installed. These concealed valve and overhead rain heads take a lot of sustained pressure to provide suitable flow for them to be really good. It really is one man's drencher is another man's light mist, depends on what you're used to.

What I'd suggest is run with what you have, put it all together and see how it is, you can always upgrade the pump as a fall back. If you are upgrading the pump then go for the most expensive one you can afford from the ST Monsoon range. Look after it and it'll last for years.

As far as negative head is concerned then again, put it all together and see if you have enough gravity flow to activate the pump, if not then you will need a universal. The trouble with these valves and heads with restrictive waterways is they are quite resistive to flow so can take at least some head to overcome that. You won't really know until you fit everything.

 

[gasbanni]

To be honest you need to get a good plumber in,
Otherwise you risk flooding your house.

That's the best advice I can give you honestly no offense but you don't know what you're doing.

 

[PASUK]

Thank you @Madrab

@gasbanni

honestly no offense but you don't know what you're doing.

Thank you - no offence taken, you are right I don't know about these shower fittings and pressure calculations but having done a fair amount of DIY central heating, soldering joints, installing new radiators and fitting sinks etc I wanted to learn how to install my bathroom and I simply have knowledge gaps in specific areas. I truly hope I don't flood the house but I recognise the risk. Hoping the forums will help plug some of the knowledge gap, and hopefully I can then build some experience.