Specifically, the boiler-side ball valve is connected the wrong way
round. I purchased a pre-made Pegler set of valves and flexible tube
and noticed it was pre-made in the same incorrect way as the ball valve
I was replacing. These small ball valves have a "flow direction" arrow
on them but are actually, unlike some taps[1], generally indifferent to
flow direction. What the arrow does relate to is the side which best
withstands static pressure when they are closed. Theory and some
practical tests suggest that pressure from the side at the back of the
arrow forces the ball against its seating and reduces the chance of
leaks. When used in a filling loop, the flow direction is towards the
boiler, but only for a tiny fraction of the life of the valve while the
boiler/CH circuit is actually being replenished. Most of the time there
is little or no pressure in the actual flexible hose and the valve is
closed against the pressure from the heating circuit, of the order of 1
or 2 bar. Therefore, for reliability the valve should be mounted
against the nominal flow direction with the back of the arrow towards
the heating circuit the arrow *towards* the loop. It seems that both
Pegler and my plumber think differently, which is perhaps why I am
having to replace the valve because of a leak round the spindle after a
year of very occasional use. I am aware that they tend to leak when
unused for a long time and then turned, but perhaps this is more likely
if lime-bearing water has got into the seal because mounting them the
wrong way round allows a slight space to develop under pressure.

[1] Taps with a washer on a rotating jumper behave oddly or completely
fail to open when operated in the wrong flow direction. The hole in a
ball valve is symmetrical and there are minimal forces in either direct
on the ball when it is opened.


--

Roger Hayter

Roger Hayter wrote:

Specifically, the boiler-side ball valve is connected the wrong way
round. I purchased a pre-made Pegler set of valves and flexible tube
and noticed it was pre-made in the same incorrect way as the ball valve
I was replacing. These small ball valves have a "flow direction" arrow
on them but are actually, unlike some taps[1], generally indifferent to
flow direction. What the arrow does relate to is the side which best
withstands static pressure when they are closed. Theory and some
practical tests suggest that pressure from the side at the back of the
arrow forces the ball against its seating and reduces the chance of
leaks. When used in a filling loop, the flow direction is towards the
boiler, but only for a tiny fraction of the life of the valve while the
boiler/CH circuit is actually being replenished. Most of the time there
is little or no pressure in the actual flexible hose and the valve is
closed against the pressure from the heating circuit, of the order of 1
or 2 bar. Therefore, for reliability the valve should be mounted
against the nominal flow direction with the back of the arrow towards
the heating circuit the arrow *towards* the loop. It seems that both
Pegler and my plumber think differently, which is perhaps why I am
having to replace the valve because of a leak round the spindle after a
year of very occasional use. I am aware that they tend to leak when
unused for a long time and then turned, but perhaps this is more likely
if lime-bearing water has got into the seal because mounting them the
wrong way round allows a slight space to develop under pressure.

[1] Taps with a washer on a rotating jumper behave oddly or completely
fail to open when operated in the wrong flow direction. The hole in a
ball valve is symmetrical and there are minimal forces in either direct
on the ball when it is opened.

On reflection they also fail when used as usually-open isolating valves
and unused for many years, so the above is not the only failure mode.
But I think it is one cause of early failure.


--

Roger Hayter

On 27/09/2018 15:14, Roger Hayter wrote:
Specifically, the boiler-side ball valve is connected the wrong way
round. I purchased a pre-made Pegler set of valves and flexible tube
and noticed it was pre-made in the same incorrect way as the ball valve
I was replacing. These small ball valves have a "flow direction" arrow
on them but are actually, unlike some taps[1], generally indifferent to
flow direction. What the arrow does relate to is the side which best
withstands static pressure when they are closed. Theory and some
practical tests suggest that pressure from the side at the back of the
arrow forces the ball against its seating and reduces the chance of
leaks. When used in a filling loop, the flow direction is towards the
boiler, but only for a tiny fraction of the life of the valve while the
boiler/CH circuit is actually being replenished. Most of the time there
is little or no pressure in the actual flexible hose and the valve is
closed against the pressure from the heating circuit, of the order of 1
or 2 bar. Therefore, for reliability the valve should be mounted
against the nominal flow direction with the back of the arrow towards
the heating circuit the arrow *towards* the loop. It seems that both
Pegler and my plumber think differently, which is perhaps why I am
having to replace the valve because of a leak round the spindle after a
year of very occasional use. I am aware that they tend to leak when
unused for a long time and then turned, but perhaps this is more likely
if lime-bearing water has got into the seal because mounting them the
wrong way round allows a slight space to develop under pressure.

[1] Taps with a washer on a rotating jumper behave oddly or completely
fail to open when operated in the wrong flow direction. The hole in a
ball valve is symmetrical and there are minimal forces in either direct
on the ball when it is opened.



I had endless trouble with the filling loop, with a stooopid little
plastic lever on the valve. Replaced it with a proper stopcock and
problem solved.

GB wrote:

On 27/09/2018 15:14, Roger Hayter wrote:
Specifically, the boiler-side ball valve is connected the wrong way
round. I purchased a pre-made Pegler set of valves and flexible tube
and noticed it was pre-made in the same incorrect way as the ball valve
I was replacing. These small ball valves have a "flow direction" arrow
on them but are actually, unlike some taps[1], generally indifferent to
flow direction. What the arrow does relate to is the side which best
withstands static pressure when they are closed. Theory and some
practical tests suggest that pressure from the side at the back of the
arrow forces the ball against its seating and reduces the chance of
leaks. When used in a filling loop, the flow direction is towards the
boiler, but only for a tiny fraction of the life of the valve while the
boiler/CH circuit is actually being replenished. Most of the time there
is little or no pressure in the actual flexible hose and the valve is
closed against the pressure from the heating circuit, of the order of 1
or 2 bar. Therefore, for reliability the valve should be mounted
against the nominal flow direction with the back of the arrow towards
the heating circuit the arrow *towards* the loop. It seems that both
Pegler and my plumber think differently, which is perhaps why I am
having to replace the valve because of a leak round the spindle after a
year of very occasional use. I am aware that they tend to leak when
unused for a long time and then turned, but perhaps this is more likely
if lime-bearing water has got into the seal because mounting them the
wrong way round allows a slight space to develop under pressure.

[1] Taps with a washer on a rotating jumper behave oddly or completely
fail to open when operated in the wrong flow direction. The hole in a
ball valve is symmetrical and there are minimal forces in either direct
on the ball when it is opened.



I had endless trouble with the filling loop, with a stooopid little
plastic lever on the valve. Replaced it with a proper stopcock and
problem solved.

The little ball valves are generally rubbish. I hoped the Pegler one
would be better than average, but I'm not very confident.

--

Roger Hayter