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.




--

Roger Hayter

Roger Hayter wrote:
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.


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

--
Trolls AND TROLL FEEDERS all go in my kill file

On 30/06/2016 15:00, Roger Hayter wrote:
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);

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

b) related to flow resistance; unlikely given full-bore geometry;

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.

c) related to pressure resistance to leaks.

Can't see it making any difference.

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

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

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.

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.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 30/06/2016 15:00, Roger Hayter wrote:
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.





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.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

John Rumm wrote in news:U5-
:

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.

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

On 30/06/2016 17:00, DerbyBorn wrote:
John Rumm wrote in news:U5-
:

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.

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

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


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Thursday, 30 June 2016 15:00:16 UTC+1, Roger Hayter wrote:
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.





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.

harry wrote:

On Thursday, 30 June 2016 15:00:16 UTC+1, Roger Hayter wrote:
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.





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.

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?)




--

Roger Hayter

On Thu, 30 Jun 2016 19:46:06 +0100, (Roger Hayter)
wrote:

harry wrote:

On Thursday, 30 June 2016 15:00:16 UTC+1, Roger Hayter wrote:
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.





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.

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?)

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


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On 30/06/2016 21:08, Archibald Tarquin Blenkinsopp wrote:
On Thu, 30 Jun 2016 19:46:06 +0100, (Roger Hayter)
wrote:

harry wrote:

On Thursday, 30 June 2016 15:00:16 UTC+1, Roger Hayter wrote:
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.





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.

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?)

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.

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

http://www.screwfix.com/p/full-bore-...lve-15mm/80413

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




--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm wrote:

On 30/06/2016 21:08, Archibald Tarquin Blenkinsopp wrote:
On Thu, 30 Jun 2016 19:46:06 +0100, (Roger Hayter)
wrote:

harry wrote:

On Thursday, 30 June 2016 15:00:16 UTC+1, Roger Hayter wrote:
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.





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.

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?)

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.

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

http://www.screwfix.com/p/full-bore-...lve-15mm/80413

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

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.



--

Roger Hayter

On 01/07/2016 00:14, Roger Hayter wrote:
John Rumm wrote:

On 30/06/2016 21:08, Archibald Tarquin Blenkinsopp wrote:
On Thu, 30 Jun 2016 19:46:06 +0100, (Roger Hayter)
wrote:

harry wrote:

On Thursday, 30 June 2016 15:00:16 UTC+1, Roger Hayter wrote:
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.





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.

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?)

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.

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

http://www.screwfix.com/p/full-bore-...lve-15mm/80413

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

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.

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


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Thu, 30 Jun 2016 21:53:18 +0100, John Rumm wrote:

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

http://www.screwfix.com/p/full-bore-...lve-15mm/80413

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

Personally I prefer to use Pegler - more expensive but, I hope, good
quality.
http://www.screwfix.com/c/heating-pl...ves/cat3830014
several on that page.

At work I always used stainless steel full-bore ball valves. Haven't seen
any on plumbing sites.
--
Peter.
The gods will stay away
whilst religions hold sway

---
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Roger Hayter wrote:
John Rumm wrote:
..

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

http://www.screwfix.com/p/full-bore-...lve-15mm/80413

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

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.


Full bore?

Tim

--
Trolls AND TROLL FEEDERS all go in my kill file

On Thursday, 30 June 2016 19:46:10 UTC+1, Roger Hayter wrote:
harry wrote:

On Thursday, 30 June 2016 15:00:16 UTC+1, Roger Hayter wrote:
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.





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.

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?)



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.

On 01/07/2016 08:38, PeterC wrote:
On Thu, 30 Jun 2016 21:53:18 +0100, John Rumm wrote:

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

http://www.screwfix.com/p/full-bore-...lve-15mm/80413

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

Personally I prefer to use Pegler - more expensive but, I hope, good
quality.
http://www.screwfix.com/c/heating-pl...ves/cat3830014
several on that page.

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

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

Mike

In article , Muddymike
wrote:
On 01/07/2016 08:38, PeterC wrote:
On Thu, 30 Jun 2016 21:53:18 +0100, John Rumm wrote:

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

http://www.screwfix.com/p/full-bore-...lve-15mm/80413

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

Personally I prefer to use Pegler - more expensive but, I hope, good
quality.
http://www.screwfix.com/c/heating-pl...ves/cat3830014
several on that page.

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

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

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

Mike

--
from KT24 in Surrey, England

harry wrote:

On Thursday, 30 June 2016 19:46:10 UTC+1, Roger Hayter wrote:
harry wrote:

On Thursday, 30 June 2016 15:00:16 UTC+1, Roger Hayter wrote:
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.





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.

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?)



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.

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

Tim+ wrote:

Roger Hayter wrote:
John Rumm wrote:
.

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

http://www.screwfix.com/p/full-bore-...lve-15mm/80413

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

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.


Full bore?

Tim

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

harry wrote:

On Thursday, 30 June 2016 15:00:16 UTC+1, Roger Hayter wrote:
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.





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.

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.

--

Roger Hayter