Stumped!!

[Rosebery]

Replacement bathroom fit. Conventional gravity installation.

Static head 2m between water level in CW tank and highest part of bath mixer.

Cold feeds direct from CW storage tank in roof in new 22mm Hep across floor of loft then straight down into bathroom. Take-off for loo first in 15mm then 15mm for WHB finally still in 22 to bath shower mixer.

Hot feed from HW storage cylinder via old (1957) 3/4" steel barrel from tank then under bedroom floor then convert to 22mm Hep in bathroom. 15mm take off for WHB, 2nd 15mm take-off for HW tap in kitchen then to BSM in 22.

Hot flow at kitchen tap excellent (not surprising - good head) old washer tap. Not mixer BTW. Cold in kitchen is direct from mains - separate tap.

Both BSM and new WHB mixer tap are 1/4 turn ceramic disk type rated for min pressure 0.2 bar - so perhaps a tad marginal. Both have U shaped Both fitted with flexi connectors and service valves. WHB is monobloc so 8mm screw fitting into base of tap.

All gate valves / service valves fully open. Both hot and cold cleared for airlocks using w/m connections in kitchen using mains. For cold airlock check used cross flow method hot to cold in BSM.

Flow at both fittings is carp. Haven't measured actual flow rate though. Basin livable with (just). Shower really not good but expected that. Diverter valve operation is via lever operated cam - doesn't require pressure to hold it up. Probably add pump when can afford it. Bath tap flow is appalling though and bath takes eons to fill and that is current problem.

Also although flow rate at bath in both hot and cold approx the same and pressure is same (both from CW storage tank) cold always overrides hot when both fully open on the mixer.

Pressure could be increased by pumping or raising CW tank I guess. 1st a possibility but 2nd rather over the horizon at present.

Any other ideas please as either to cause or solution? I'm fresh out!!

Thanks

 

[Softus]

When you say "highest point of bath mixer", is this the spout or the shower handset?

If the former, then 2m from water level to spout isn't enough for taps that need a 0.2 bar minimum. For the WHB taps the situation is worsened by the 15mm Hep2o and then the 8mm flexibles.

Other thoughts:

Are those flexible hoses kinked?

What type of service valves have you used?

If you unmount the BSM and connect both inlets to a mains cold supply, e.g. adapted from the garden tap, do you get a decent flow?

 

[Rosebery]

When you say "highest point of bath mixer", is this the spout or the shower handset?

Sorry - should have been clearer. Spout which is an up and over U shape. This highest point is about 9" above the level of the edge of the bath.

If the former, then 2m from water level to spout isn't enough for taps that need a 0.2 bar minimum. For the WHB taps the situation is worsened by the 15mm Hep2o and then the 8mm flexibles.

Nothing can be done about the flexis on WHB monobloc I think. Live with it or change the tap??

Are those flexible hoses kinked?

No not at all.

What type of service valves have you used?

Compresion Ballofix on WHB but not full bore as the 8mm screwin flexis that came with it seemed to be limiting factor. On bath they are pushfit valves (plastic screw adjust) integrally mounted on flexi with 3/4" tap connector at other end. BSM is normal 3/4" tap connector fitting.

If you unmount the BSM and connect both inlets to a mains cold supply, e.g. adapted from the garden tap, do you get a decent flow?

Haven't unmounted it but used mains from washing machine cold feed first into redundant hot wash m/c feed to clear any possible airlock in hot then using crossflow method in BSM to clear cold. Although in both cases the mains would have been fighting the gravity (I guess) with the BSM divertor set to taps rather than shower the flow was only marginally better. Should I try it direct with both hot and cold gravity feeds off?

 

[Softus]

If the former, then 2m from water level to spout isn't enough for taps that need a 0.2 bar minimum. For the WHB taps the situation is worsened by the 15mm Hep2o and then the 8mm flexibles.

Nothing can be done about the flexis on WHB monobloc I think. Live with it or change the tap?

Yes, or pump it (as you'd already suggested).

What type of service valves have you used?

Compresion Ballofix on WHB but not full bore as the 8mm screwin flexis that came with it seemed to be limiting factor.

I think you're making what I suspect is a common mistake, in thinking that the smallest point of constriction is the only factor in reducing flow. This isn't the case. There would be a significant difference between 22mm and 15mm pipework leading to the same 8mm bore flexible. Every single swept bend, elbow, reducer, valve, and every coupling and straight length of pipe, each adds resistance and/or turbulence to the flow of water. If you want to give your taps the best supply, then use only full bore valves and fittings.

On bath they are pushfit valves (plastic screw adjust) ...

Do you mean John Guest service valves? Those are very restrictive.

If you unmount the BSM and connect both inlets to a mains cold supply, e.g. adapted from the garden tap, do you get a decent flow?

Haven't unmounted it but used mains from washing machine cold feed first into redundant hot wash m/c feed to clear any possible airlock in hot then using crossflow method in BSM to clear cold.

I didn't meanfor the purpose of clearing air, but for measuring the flow you'd get if the supplies were form the mains.

...Although in both cases the mains would have been fighting the gravity (I guess) with the BSM divertor set to taps rather than shower the flow was only marginally better.

I surmise that with the gravity supplies still connected to the taps, water would emerge from the DHW vent (or, if the rate was slow, from the DHW cold feed at the CSS outlet) - this wouldn't give you the right indication of what flow rate could be achieved with a pump.

Should I try it direct with both hot and cold gravity feeds off?

Yes. Off from the taps that is. Under no circumstances should you, for example, close the cold feed to the cylinder and block the DHW vent, because that would pressurise the cylinder - damaging it would be both messy and expensive.

 

[Rosebery]

If the former, then 2m from water level to spout isn't enough for taps that need a 0.2 bar minimum. For the WHB taps the situation is worsened by the 15mm Hep2o and then the 8mm flexibles.

Nothing can be done about the flexis on WHB monobloc I think. Live with it or change the tap?

Yes, or pump it (as you'd already suggested).

Thanks.

What type of service valves have you used?

Compresion Ballofix on WHB but not full bore as the 8mm screwin flexis that came with it seemed to be limiting factor.

I think you're making what I suspect is a common mistake, in thinking that the smallest point of constriction is the only factor in reducing flow. This isn't the case. There would be a significant difference between 22mm and 15mm pipework leading to the same 8mm bore flexible. Every single swept bend, elbow, reducer, valve, and every coupling and straight length of pipe, each adds resistance and/or turbulence to the flow of water. If you want to give your taps the best supply, then use only full bore valves and fittings.

OK I'll change the WHB ones to full bore. BTW the 22mm run goes right underneath the WHB so the 15mm element is only the riser.

On bath they are pushfit valves (plastic screw adjust) ...

Do you mean John Guest service valves? Those are very restrictive.

Well they're similar but look more like This

If you unmount the BSM and connect both inlets to a mains cold supply, e.g. adapted from the garden tap, do you get a decent flow?

Haven't unmounted it but used mains from washing machine cold feed first into redundant hot wash m/c feed to clear any possible airlock in hot then using crossflow method in BSM to clear cold.

I didn't meanfor the purpose of clearing air, but for measuring the flow you'd get if the supplies were form the mains.

Yes I see what you mean but I'd thought it might have been giving me some indication of what mains would be like coming out of the taps.

...Although in both cases the mains would have been fighting the gravity (I guess) with the BSM divertor set to taps rather than shower the flow was only marginally better.

I surmise that with the gravity supplies still connected to the taps, water would emerge from the DHW vent (or, if the rate was slow, from the DHW cold feed at the CSS outlet) - this wouldn't give you the right indication of what flow rate could be achieved with a pump.

From the relevant outlets in the CW storage tank.

Should I try it direct with both hot and cold gravity feeds off?

Yes. Off from the taps that is. Under no circumstances should you, for example, close the cold feed to the cylinder and block the DHW vent, because that would pressurise the cylinder - damaging it would be both messy and expensive.

Yes I understand.

Have you any idea why the cold would override the hot in the BMS though in a system with roughly equivalent (albeit slow) flow and the same static head?

Thanks your help.

 

[Softus]

BTW the 22mm run goes right underneath the WHB so the 15mm element is only the riser.

Noted.

On bath they are pushfit valves (plastic screw adjust) ...

Do you mean John Guest service valves? Those are very restrictive.

Well they're similar but look more like [img]

Hm. They're still quite narrow and they're spherical (aka ball-o-fix) valves.

I didn't mean for the purpose of clearing air, but for measuring the flow you'd get if the supplies were from the mains.

Yes I see what you mean but I'd thought it might have been giving me some indication of what mains would be like coming out of the taps.

Not a hope - the mains will find the path of least resistance, and the existence of the open vent will make a mockery if trying to shepherd the water through the bath taps.

I surmise that with the gravity supplies still connected to the taps, water would emerge from the DHW vent (or, if the rate was slow, from the DHW cold feed at the CSS outlet) - this wouldn't give you the right indication of what flow rate could be achieved with a pump.

From the relevant outlets in the CW storage tank.

OK, but the vent was still open, wasn't it?

Have you any idea why the cold would override the hot in the BMS though in a system with roughly equivalent (albeit slow) flow and the same static head?

I've seen the same thing even with taps that give great flow with very little head. I would expect gravity cold to always defeat gravity hot at low flow rates.

 

[Rosebery]

Hm. They're still quite narrow and they're spherical (aka ball-o-fix) valves.

I'll replace them with full bore valves then. Still use flex or should I do the last bit from the valve to the tap in copper?

Not a hope - the mains will find the path of least resistance, and the existence of the open vent will make a mockery if trying to shepherd the water through the bath taps.

Yes - forgot about the vent.

OK, but the vent was still open, wasn't it?

Errm well yes it was!

Have you any idea why the cold would override the hot in the BMS though in a system with roughly equivalent (albeit slow) flow and the same static head?

I've seen the same thing even with taps that give great flow with very little head. I would expect gravity cold to always defeat gravity hot at low flow rates.

So if I get the flow rate up then it should be OK?

 

[Softus]

I'll replace them with full bore valves then. Still use flex or should I do the last bit from the valve to the tap in copper?

Personally, I avoid flexibles wherever I can. If you have copper tails that fit then go for it, but sometimes the 'O' rings don't sit in the right place to make a seal. You can but try.

So if I get the flow rate up then it should be OK?

Finding the answer to that is the purpose of the experiment.

So, without changing anything (yet), I would find out what the flow is like when you put cold mains through the flexibles and the taps. If good, then you know that you've merely got to increase the pressure/flow, which a pump would achieve. However, you might gain enough improvement with the other ideas such that you could make do without a pump.

 

[Softus]

( stopping supply to cylinder & blocking vent will damage it)

That's correct, which is why I already advised the OP not to do that.

Change your cold supply to mains fed for a start.

That will result in unbalanced supplies to the BSM, so is a ludicrous thing to do.

 

[Rosebery]

Change your cold supply to mains fed for a start.

Well even I know thats total f......... nuts with gravity hot into a bath shower mixer.

Oh I get it bambi. First change to cold mains, then you might as well have a combi and get rid of the tanks as well. But won't the BSM struggle with a combi. Oh well never mind I'll change that too!

 

[Rosebery]

Thanks Mod 9. Sorry - but he was winding me up. At least he did apologise before that one went as well.

 

[Rosebery]

Mmmm. Clearly a long running saga between you two guys.

Thanks for your input Softus. I'll have another go next weekend.