Megaflow or open vented system

[blueagle78]

Also got to ask a question about hot water cylinder. Based on your recommendations I was thinking of getting OSO Super S hot water cylinder but the problem is its too big for my airing cupboard. We won't be able to fit 570mm diameter cylinder in there as space is tight and 570mm would mean door won't shut properly.
Another local plumb shop sells RM with 25 years warranty and as the diameter is 545mm it would fit in the airing cupboard. I would like to know if one of you have used RM unvented cylinder and if so what you think of them?

 

[Agile]

I measured the water flow based on stopwatch and bucket method as suggested. I got just over 20l/min. While I did it I was getting the new pipe from mains anyway. So I measured the flow again last night once the new pipe was fitted and we had 22mm pipe indoors rather than 15mm. I must say I got around 24-25l/minute. So now hopefully I shouldn't have problem with the water pressure even when 2 or 3 showers are being used at the same time.
.
Thanks

I keep telling you that you need to measure the dynamic flow rate.

But you just measure the open pipe flow rate!

Tony

 

[mysteryman]

Someone mentioned the balanced pressure cold offtake. This is for shower or other mixers only - it is NOT for all cold outlets in the house.

Also, check the heat transfer power of the coil in your OSO - they were only 10kW on some versions, which is not enough.

 

[muggles]

Someone mentioned the balanced pressure cold offtake. This is for shower or other mixers only - it is NOT for all cold outlets in the house

That's an interesting observation. Care to explain why?

Also, check the heat transfer power of the coil in your OSO - they were only 10kW on some versions, which is not enough.

It's 26kW on the 250l, as it is in the rest of the range except the smallest one, which is 12kW, none of them are 10kW

 

[mysteryman]

It is specifically there to provide a balanced pressure cold supply to mixers such as showers. Taking cold taps and loo cistern supplies from it defeats the purpose.

 

[Norcon]

But in a large property mm that means piping an additional cold supply upstream of the UV combination valve. Extra pipework = extra cost!
For very little benefit imo.
A shower mixer say in an ensuite using 12l/min with 60c hot supply and 5c cold will use 33% cold and 66% hot to deliver 41c.
So its not a big demand on the balanced cold and the pipe sized appropiately.

 

[mysteryman]

That is not the problem. The first problem is: when someone opens a cold tap fully, the pressure drops along the cold supply pipe, while the hot is unaffected, and the shower runs hot. The other problem is: there's a fault on the cylinder or the immersion. The cold supply is turned off. Most of the cold taps and the loo cisterns have no supply - because of a cylinder problem.

Which bit of "Balanced pressure cold supply for mixers" don't you understand?

A bit of extra cost should not stop you doing your job properly.

 

[Norcon]

The first problem is: when someone opens a cold tap fully

In an ensuite thats rare when someone is in the shower. And even if they did, with the basin flow set, it will not affect the shower.
You size the pipes accordingly. No need for an extra pipe run.

 

[mysteryman]

It is not just the taps in the en suite. You are trying to justify doing something wrong.

 

[Norcon]

Nothing wrong about balanced h&c supplies to an ensuite using two pipes.
Then you have towel rail f&r, (say an uf heated property) and secondary return. Thats five.
And you want a sixth one added.

 

[holty]

come on lads, i can see either point . in a real world it would be good to repipe with mysterymans suggestion, but as norcon has said its a lot of cost. for no real gain. when times are hard and people what little cost.most will balance a house as any other way will be non cost effective. as to the OP. think agile is trying to tell you something. and another poster came up with what would needed to be done. e.g getting 24l a min is great at one tap. till you go round and see what each outlet it will produce. seen 20l plus at kitchen taps then when a basin up stairs for e.g. a tap is introduced or a toilet flushing. the flow rate can decrease at some outlets from 16 down to 6l a min. then causing future problems when a shower is introduced. going around sticking a pressure gauge on and checking only one tap aint all its about.

 

[holty]

p.s by the way for the sake of a few extra quid. some full bore valves or one valve and a check valve. its easy to isolate the cylinder but bypass the balanced feed.

 

[mysteryman]

This is a DIY forum, and I am trying to explain to them how it should be done. They are not on here looking for advice on how to do it wrongly from you guys who should know better.

As I said before, which bit of 'Balanced pressure cold supply for mixers' can't you understand?

 

[transam]

RM cylinders fitted quite a few , 25 year warranty well like alot of these eye catching long warrantys offered by various manus ect , time will tell maybe ???

unvented / Accumulaters , they can be used in conjuction with a patented mains pump which has wras approval , a type booster for the accumulater , supplied by RM cylinders .

 

[Norcon]

As I said before, which bit of 'Balanced pressure cold supply for mixers' can't you understand?

The part that requires an extra run of pipe work to say an ensuite for no extra benefit and a lot of extra cost.

And also, since you seem to be advocating connecting the basin upstream of the uv combination valve with an extra run of pipe you then will likely have unbalanced pressures to that tap. (ie. main incoming prv set to 4 bar and uv prv set to 2 bar)

So take a tap that mixes in the body and seals fail or the tap goes porous and you then have a high pressure back feed to the unvented cylinder!
Yeah very clever. So its call back time or some poor s*od over the internet,, help help , my unvented cylinder is reading 5 bar pressure and the instructions say it shouldn't go past 2 bar. What should I do? Someone says they can explode help help.