Cold Water Storage Tank Increase Filling Rate

10 Jun 2018
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United Kingdom
Hi, Just a few queries I wonder If I can get some advice with please
I'm shortly going to be fitting a new bathroom. Part of this will be fitting a Mira Atom shower with 2 shower heads and am planning to fit a Salamander 1.5 bar CT50 xtra Pump in the airing cupboard to feed shower only. I will be plumbing in myself. Have already taken separate supply from CWST to pump location in 22mm pipe, to be reduced to 15mm just before the Pump connector.
Its a 1 1/2 storey house with CWST in very tight Loft space. Hot water cylinder ( Indirect, Vented 140 Ltrs ) on First Floor, and Shower on Ground floor approx. 2.5 Meters from Shower head to bottom of CWST. Upstairs also has a wall fitted Redring 520TS Pumped power shower
Questions I have are

1) All Pumps I looked at online state a minimum of 50 Gallons CWST capacity. My Tank is 40 Gallons. Now I know that this does not comply with the Pump warranty, and there's not a lot I can do about this except hope the pump runs for at least a couple of years before I have to buy another. This limitation is one of the reasons I didn't go for a higher spec / quality Pump such as a CT force or ST monsoon. There's no chance of fitting a bigger Tank dues to space limitations. Fitting an extra tank is just also physically not possible. Its just me and the Missus in the house so demand on water is not high. Very rarely would both upstairs and downstairs showers be in use, but when family come to stay, it would be quite possible that both are. The CWST is a Ferham FLT 40 coffin type tank, with a Lid on each end of the Tank. I have limited access to each end of the tank also by a loft hatch each end. My question is, is there any reg or reason I could not if another Ball valve on the other end of the Tank to Decrease the rate at which the tank level drops when the shower pump, and also other shower are in use , Mains water pressure to the tank is good, so I'm sure there is enough pressure to sustain two supply's to the tank. If not possible, are there faster filling Ball valves that may be an option to prevent tank level becoming to low to quickly.. Maybe 40 Gallon tank will be plenty ???

2) The hot water supply for the Pump will be coming from the side of the HWC. There is a Secondary return plug in just the right position, just below the dome of the tank and above Pump position. Instead of using an Essex Flange ( Don't have the Bottle to cut a hole in the tank, and due to Tank being close to the slope of the roof, no room to use one of the recommended Top fitting flanges unless I uncouple the tank and move it over to fit the Flange) I have a 1" to 22mm fitting that I will replace the Plug with. I have ground the pipe stop from inside the fitting , so the 22mm pipe will go through into the Tank. Has anybody done or heard of this before, or foresee any problems with this idea ?

Any advice would be appreciated
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Assuming both showers are both pumped and pump both cold & hot ?. Having recently looked into this - 40 gallons for your CWST should be fine. However, I don't think you have enough hot water to run two showers anyway (either simultaneously or one after another) without it running cold so the size of your CWST becomes irrelevant if you don't have the hot water capacity.
Mark 9002,
Maybe 40 Gallon tank will be plenty ???

Have you measured the usable capacity of your coffin 40 gallon tank ? Usually the usable capacity is taken for granted but for your unique proposed pump install its important.

If you want the storage tank to fill quicker,fit a low pressure ball valve but consider the effects of aeration in the 40 gallon tank :!:. The low pressure ballvalve could result in noise while filling but the pump noise will be louder :(.

Also consider water starvation in relation to prevention of scalding.

The heat source to the hot water cylinder has to be sufficient to provide quick reheat,Dont want to be running out of stored hot water.

Personally i would advise an unvented cylinder is correctly installed, then you wont need 2 shower pumps (y)
Many Thanks for the reply's.
The shower that is being replaced downstairs was an old Mira Gravity fed mixer shower ( fitted in 1992). The flow through a single head was OK'ish but not invigorating. Our heating is normally with the Oil boiler ( No mains gas up here in Orkney islands ) Up to now, we heat the water for an hour in the Morning, and the Missus used downstairs shower, I used Power shower upstairs and it still seems like there's enough hot water to do the dishes in the evening. I appreciate that having 2 pumped showers will change this. If I believe Miras Bumf that the new shower has dramatically increased flow technology, ( min Pressure 01. bar and I guess it would get 0.2 ish) so maybe would be a bit more than OK'ish Gravity fed. The main concern of mine was not to run the CWST / Shower pump dry, and if the water starts getting cold we could put on 3KW immersion and Oil heating for quick reheat. This is our usual procedure when family stay. Like I mentioned earlier, both showers are never in use at the same time anyway unless family stay. As a standby, I am thinking to fit bypass pipes between pump inlet and outlet Piping with Ball Valves for isolation. After closing pump isolating V/Vs and unplugging pump, the shower could then go on gravity if it gives a reasonable flow,and looks like 2 showers will be in use at one time. to reduce the demand on CWST and hot water. This is just going to be a short term plan.
Just a couple more questions if I may
Fitting a low pressure V/V to CWST seems like a viable alternative to my thought of fitting another float V/V. It may be more noisy but I could try and wrap more insulation around the tank. The Shower suctions are at the opposite end of the tank to the inlet so hopefully most aeration
may have dissipated ???.
The long term plan. At some time in the future we were planning on fitting en suite in one bedroom. My thoughts were leaning towards an Electric shower for this, but I had never considered getting a closed vent tank installed. Not sure really how this system works, but does it also need a change of boiler ???
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If you have circa 22l/p and 2+ bar from your incoming main and can route this in 22mm pipe to where you would put a UV cylinder, then that would be the best option for you as space in the loft is obviously very tight... You can then lose the CWSC completely. It will work exactly the same as your current O/V cylinder but will just be fed by main rather than tank. Should be no need to change boiler but will need to be installed and serviced annually by a G3 engineer... It will also need a suitable route for safety discharge pipework.
The ball valve is quite restrictive to flow. It's possible to fit a larger 3/4" valve (which fits a 22mm pipe) instead of the usual 1/2" valve which fits 15mm pipe. I found it also runs quieter, as well as delivering water quicker. This is a fairly easy swap, but you will need an adaptor on the pipe. If you can manage to run a new 22mm pipe, so much the better. Look at any service valves or stopcocks on the supply and change them for full-bore ones, to get the best flow.

Downside is that the 3/4" is more expensive, and a replacement washer is harder to find (buy a spare cone and washer and leave them in the packet tied to a handy rafter next to the tank)
Thanks to All that have helped me here.
JohnD Re the Ball V/V's, my plan is to fit 22mm pipe work & Ball V/Vs to and from the Pump ( although it has 15mm connectors ) and reduce again to 15mm just before the shower connections. This would also include the Bypass pipes I intend to fit. I'll try and use swept bends in Pipe work where possible to give as little flow restrictions to the shower as possible.
The seed of though has definitely been planted in my head now Re UV cylinder which I had never considered. Mains pressure is good. We only open the stop cock approx. 1/2 of a turn, or else there to much pressure on the Kitchen tap, so 22 LPM should be no problem. the 22mm mains feed to the CWST Runs up the slope of the roof just above the HWC in the airing Cupboard so I guess that's the future feed for UV cylinder and I'm guessing safety discharge pipework can go straight from Cupboard through Facia or soffit which is just next to Cupboard. Yes, definitely think this will be the way to go when the Future En suite goes ahead. Just need to make enquiry's if there's a G3 installer available Locally. Does anybody have a rough Ball park figure on cost of installation ?

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