Why do service valves (15mm and 22mm) have an arrow indicating direction of flow?

Rednadnerb wrote:
Why do service valves (15mm and 22mm) have an arrow indicating direction of flow?

Because the pressure in the direction of flow tends to help them seal.
It is the same with most valves but not all.

To seal what? there is a compression joint at each end and a ball valve in the middle.

On Tuesday, 15 November 2016 17:51:34 UTC, Rednadnerb wrote:
To seal what? there is a compression joint at each end and a ball valve in the middle.

To prevent water passing through the valve when it is in the "off" position.

Rednadnerb wrote:
Why do service valves (15mm and 22mm) have an arrow indicating
direction of flow?

It's so that you put the arrow on the valve pointing away from the
pressurised end, eg, the incoming water main, so that somone can turn it off
and cut into the pipe on the other side without flooding the house with
mains pressure.

Most pipework isn't always fully visible and in full view...it's all pretty
obvious if it's 12 inches away from a toilet or basin, but what if it's
halfway along a horizontal pipebox in a bedroom?

On 11/15/2016 7:04 PM, Phil L wrote:
Rednadnerb wrote:
Why do service valves (15mm and 22mm) have an arrow indicating
direction of flow?

It's so that you put the arrow on the valve pointing away from the
pressurised end, eg, the incoming water main, so that somone can turn it off
and cut into the pipe on the other side without flooding the house with
mains pressure.

Most pipework isn't always fully visible and in full view...it's all pretty
obvious if it's 12 inches away from a toilet or basin, but what if it's
halfway along a horizontal pipebox in a bedroom?


Well that helps, but I am still with Harry on the basic reason.

Sorry, I still don't get it.
If I installed it with the arrow pointing in the wrong direction would it not work?

Rednadnerb wrote

Sorry, I still don't get it.

If I installed it with the arrow pointing in the wrong direction would it
not work?

Not necessarily as well, particularly when the flow is turned
off completely, it may leak a bit if its installed the wrong way.

On 11/15/2016 7:46 PM, Rod Speed wrote:
Rednadnerb wrote

Sorry, I still don't get it.

If I installed it with the arrow pointing in the wrong direction would
it not work?

Not necessarily as well, particularly when the flow is turned
off completely, it may leak a bit if its installed the wrong way.

What a day. Agreeing with Harry *and* Rod.

newshound wrote
Rod Speed wrote
Rednadnerb wrote

Sorry, I still don't get it.

If I installed it with the arrow pointing in the wrong direction would
it not work?

Not necessarily as well, particularly when the flow is turned
off completely, it may leak a bit if its installed the wrong way.

What a day. Agreeing with Harry *and* Rod.

I'd have you publicly flogged if you hadn't enjoyed that so much the last
time.

Rednadnerb wrote:
Sorry, I still don't get it.
If I installed it with the arrow pointing in the wrong direction
would it not work?

Yes it would still work, but if you turned it off and then undone the
compression fitting at the end the arrow is pointing, that side would still
be live and the other end would be dead

Phil L wrote:
Rednadnerb wrote:
Sorry, I still don't get it.
If I installed it with the arrow pointing in the wrong direction
would it not work?

Yes it would still work, but if you turned it off and then undone the
compression fitting at the end the arrow is pointing, that side would still
be live and the other end would be dead




Now *that* is the most plausible reason given so far for having a direction
arrow on the valve.

Tim

--
Please don't feed the trolls

Rednadnerb wrote:

Why do service valves (15mm and 22mm) have an arrow indicating direction
of flow?

Not long ago I asked the same question on here and was given the answer,
although I have forgotten who told me. Being curious I tested it, on a
couple of good quality (Pegler) 15mm, not full bore, ball valves. In
practice, with 2 bar pressure on the side away from the arrow they don't
leak With 2 bar on the side with the arrow point they leak quite
briskly. If you look into the ends the plastic seal is squeezed firmly
between the ball and the machined and polished fitting at the arrow
point side, while on the opposite side there is a wide space closed by
some sort of clip where the ball and seal are inserted. So pressure
from the opposite side to he arrow head forces the seal and ball closed,
while in the other direction it tends to depressurise it and pull the
seal away from the housing.

(Neither would seem to affect leaking from the spindle seal, which is
how they generally fail in my experience, but maybe the better ones
don't do this. I live in hope. I suspect this seal works if it is
either used every day, or never used at all.)

--

Roger Hayter

Thanks to all and especially Roger, that's the kind of detail I was looking for.