Isolation valves - a question

[Roger Hayter]

I'm talking about the little 15mm in-line, often scewdriver operated ball valves for isolating plumbed-in tiems, in this case a Myson fan radiator. They are marked with a flow direction; is this:

a) unimportant (not very satisfying to those with obsessive tendencies); b) related to flow resistance; unlikely given full-bore geometry; c) related to pressure resistance to leaks.

The significance of this (apart from the fact that mine always leak from the spindles within a few months of fitting especially if ever operated) is that if c) is true then the one on the central heating return pipe needs fitting the wrong way round, as the high pressure side when offf is not the side flow is from in use.

Anyone any views on this question? Thanks in advance.

[Tim+]

Can't see why they would be flow sensitive. As you've found though, they're a) crap and b) restrictive. Use full bore valves if you ever hope to get a decent output from your myson.

Tim

[John Rumm]

They will certainly work both way, although some may perform better long term if used in the "correct" direction.

Ought not make any difference - you may get slightly more turbulence and hence noise in the wrong direction, but not a dramatic difference in flow.

Can't see it making any difference.

If you get decent branded ones, then you should not see any leaks.

Do you even need one in the return pipe? Either way, that is a case where a quality full bore leaver version would be preferable.

[Roger Mills]

It might matter if it's switching a mains supply with a pressure differential of several bar across it - but is unlikely to matter in a CH circulation system.

[DerbyBorn]

John Rumm wrote in news:U5- [e-mail]:

If the heater needs to be removed then yo uneed two valves.

[John Rumm]

Yup sorry, I was assuming it would have normal rad valves as well, but depending on what type it is, it might not.

[harry]

There is a soft seating material in most ball valves to make them leak resistant. This is often only on one side of the ball. So at high pressures the ball may not seat correctly with reverse flow.

Taking one to bits is quite illuminating.

[Roger Hayter]

Thanks. (And thanks to all others' comments.) So this may be a reason for using them the right way round. Of course, my argument about putting the return on the wrong way round only applies when they are both off, which should not normally be the case.

In the absence of any other convincing points I shall probably assume you are right.

I would also be tempted not to use them, but I do need building control approval in this case. And actually if one doesn't want a pipefull of water in the electrics they are quite handy in my particular arrangement. The alternative is drain valves and they are generally even worse (anyone found heatproof washers for them - I don't think they exist?)

[Archibald Tarquin Blenkinsopp]

Harry is probably right regarding the seats on metal valves, but the upvc we normally fit have the flow direction toward the screwed seat. This has the effect of putting the pressure against the exterior side of the clamping ring. The downstream side of the valve is the "closed" side of the valve body.

The net effect is to provide a "sealing" force on the clamping ring [and seat]. If fitted backwards there would be a force trying to separate out the valve components.

I don't think this is common knowledge even amongst professional fitters as large numbers of valves get fitted in the wrong direction. I have to rectify problems produced during and after manufacture. I have never to my knowledge had a problem through fitting a ball valve the wrong way, except maybe from clients who like to display their superior knowledge and snag these faults.

I don't have one to hand, but I seem to recollect that 15mm ball valves for CH have a phosphor bronze securing clamp at one end. This would no doubt be the end to which flow is directed, thus aiding the clap pressure.

AB

[John Rumm]

I think you are over thinking this... buy a decent valve like:

slap it in, it won't leak, and it does not care which way round you install it!

[Roger Hayter]

I was tempted, but I'd have to take the levers off to fit them in the space. I did get expensive Yorkshire screwdriver operated ones and i'lll report here when they start leaking.

[John Rumm]

You can get the same with a "butterfly" lever - they need less space to operate.

[PeterC]

Personally I prefer to use Pegler - more expensive but, I hope, good quality.

several on that page.

At work I always used stainless steel full-bore ball valves. Haven't seen any on plumbing sites.

[Tim+]

.

Full bore?

Tim

[harry]

Bigger ball valves have a loose ball/shaft fit that lets the ball move to assist with the seating.(Which might be metal to metal). The small one have balls fixed to the shaft, they rely on the seating material being distorted (by the stuff being transported) to make the seal.

Drain valves never get hot, they are on a "dead leg" ie there is no passage of hot material nearby. Except during a drain down. And even then the (water?) is usually cold.

[Muddymike]

Why are the red topped ones more expensive than the blue?

Mike

[charles]

I buy ones which come with both red and blue tops and you use which one you need.

[Roger Hayter]

They may never reach the full temperature of the heating fluid but they can get pretty hot by conduction in the copper. Heat cycling and hardening of the rubber washer seems to combine to make them loose. (Discounting the crass error I have committed in the past of soldering them without removing the spindle and washer!)

[Roger Hayter]

Sadly not. There is barely room for the increased lenght of the full bore ones between radiator and ceiling, let alone levers, even short/butterfly ones.

[Roger Hayter]

Thanks for this. The valves are Pretex 1254. The behaviour as isolation valves is exactly what you predict. If the flow in iside is to the high pressure they resist 10 bar with no leakage at the spindle or past the ball. If you put them the other way round there is still no spindle leakage but there is a steady, brisk trickle through them at less than 1 bar. Since I want them to be effective isolation valves with the CH pressurised up to 2 bar then I shall put them both with flow in side towards the system. I can't believe the differential pressure due to flow in the open state can make any difference, and they are not going to be used in a partially closed condition.

I expect they'lll start leaking round the spindles in a year or so and I will have to remove olives and cut the pipe or more likely use a new bit to fit full bore ones which are longer, but I am not going to bother to do that now, it was hard enough to get the pipes where they are anyway.