[graham]

I'm looking at buying a vacuum gauge, but they nearly all have BSPP
(male) threads - can anyone tell me how these are supposed to be sealed
when fitted to the BSPP female?
I've come across mention of copper crush washers and bonded washers, but
i've no idea if this is the standard technique.
Would the "crush washer" be sized to fit over the BSP thread, or inside
the female?

thanks,
graham.

[Roger Mills[_2_]]

On 06/07/2013 17:07, graham wrote:
I'm looking at buying a vacuum gauge, but they nearly all have BSPP
(male) threads - can anyone tell me how these are supposed to be sealed
when fitted to the BSPP female?
I've come across mention of copper crush washers and bonded washers, but
i've no idea if this is the standard technique.
Would the "crush washer" be sized to fit over the BSP thread, or inside
the female?

thanks,
graham.


Parallel threads normally seal on a flange and face - with a fibre or
squashable copper washer in between. Does the male thread on the gauge
have a flange?

If not, you may get away with some liquid PTFE thread sealant, but
that's not ideal.
--
Cheers,
Roger
____________
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

[graham]

Roger Mills wrote on 06/07/13 17:27:
On 06/07/2013 17:07, graham wrote:
I'm looking at buying a vacuum gauge, but they nearly all have BSPP
(male) threads - can anyone tell me how these are supposed to be sealed
when fitted to the BSPP female?
I've come across mention of copper crush washers and bonded washers, but
i've no idea if this is the standard technique.
Would the "crush washer" be sized to fit over the BSP thread, or inside
the female?

thanks,
graham.


Parallel threads normally seal on a flange and face - with a fibre or
squashable copper washer in between. Does the male thread on the gauge
have a flange?

If not, you may get away with some liquid PTFE thread sealant, but
that's not ideal.

Doesn't look like much of a flange to me - this is typical of the ones I
see: http://www.wika.co.uk/213_53_en_co.WIKA
Actually, looking at the "operating instructions" for that model it has
a little picture with the end of the BSPP thread labelled "sealing face".
So maybe a squashable washer in there?
Would htat require a special female fitting or are female BSPP threads
always a specific depth with an accurately flat bottom to the hole?

[Nightjar]

On 06/07/2013 17:07, graham wrote:
I'm looking at buying a vacuum gauge, but they nearly all have BSPP
(male) threads - can anyone tell me how these are supposed to be sealed
when fitted to the BSPP female?
I've come across mention of copper crush washers and bonded washers, but
i've no idea if this is the standard technique.
Would the "crush washer" be sized to fit over the BSP thread, or inside
the female?

A bonded washer is intended to go over the male thread and to seal
between the faces of the two fittings. A crush washer is intended to fit
inside the female fitting and be crushed by the extended male thread
that pressure gauges have. That should allow you to get the gauge facing
the right way when tightening it down and still get a seal. I have no
idea whether vacuum gauges work the same way, as I have never needed vacuum.

Colin Bignell

[Dave Plowman (News)]

In article ,
graham wrote:
Doesn't look like much of a flange to me - this is typical of the ones I
see: http://www.wika.co.uk/213_53_en_co.WIKA
Actually, looking at the "operating instructions" for that model it has
a little picture with the end of the BSPP thread labelled "sealing face".
So maybe a squashable washer in there?
Would htat require a special female fitting or are female BSPP threads
always a specific depth with an accurately flat bottom to the hole?

That looks like it's designed to take a pipe cap nut, where the flare in
the pipe does the sealing. Like brakes on a car.

--
*People want trepanners like they want a hole in the head*

Dave Plowman London SW
To e-mail, change noise into sound.

[Tim Watts[_2_]]

On Saturday 06 July 2013 17:27 Roger Mills wrote in uk.d-i-y:

On 06/07/2013 17:07, graham wrote:
I'm looking at buying a vacuum gauge, but they nearly all have BSPP
(male) threads - can anyone tell me how these are supposed to be sealed
when fitted to the BSPP female?
I've come across mention of copper crush washers and bonded washers, but
i've no idea if this is the standard technique.
Would the "crush washer" be sized to fit over the BSP thread, or inside
the female?

thanks,
graham.


Parallel threads normally seal on a flange and face - with a fibre or
squashable copper washer in between. Does the male thread on the gauge
have a flange?

If not, you may get away with some liquid PTFE thread sealant, but
that's not ideal.

It seems depressingly common that random gauges come with BSPP threads. I
had one supplied with a water pressure regulator (so it wa not a case of the
wrong choice of base). There is no way it would reach down for a washer nor
was there a decent flat shoulder to seal on.

I used several turns of Gas PTFE until it was "very tight" then wound it in
to th eposition I wanted.

However, water is rather more forgiving than gas, so I think in the OP's
case I would use a vacuum approved (gas grade) thread sealant.

I assume this is only for soft vacuum work?
--
Tim Watts Personal Blog: http://squiddy.blog.dionic.net/

http://www.sensorly.com/ Crowd mapping of 2G/3G/4G mobile signal coverage

Reading this on the web? See:
http://wiki.diyfaq.org.uk/index.php?title=Usenet

[graham]

Nightjar wrote on 06/07/13 18:04:
On 06/07/2013 17:07, graham wrote:
I'm looking at buying a vacuum gauge, but they nearly all have BSPP
(male) threads - can anyone tell me how these are supposed to be sealed
when fitted to the BSPP female?
I've come across mention of copper crush washers and bonded washers, but
i've no idea if this is the standard technique.
Would the "crush washer" be sized to fit over the BSP thread, or inside
the female?

A bonded washer is intended to go over the male thread and to seal
between the faces of the two fittings. A crush washer is intended to fit
inside the female fitting and be crushed by the extended male thread
that pressure gauges have. That should allow you to get the gauge facing
the right way when tightening it down and still get a seal. I have no
idea whether vacuum gauges work the same way, as I have never needed
vacuum.

Colin Bignell



ahh, thanks. Does one need a special female fitting suitable for a small
crush washer or is t a standard shape of all female BSPP fittings?

graham

[graham]

Tim Watts wrote on 06/07/13 20:04:
On Saturday 06 July 2013 17:27 Roger Mills wrote in uk.d-i-y:

On 06/07/2013 17:07, graham wrote:
I'm looking at buying a vacuum gauge, but they nearly all have BSPP
(male) threads - can anyone tell me how these are supposed to be sealed
when fitted to the BSPP female?
I've come across mention of copper crush washers and bonded washers, but
i've no idea if this is the standard technique.
Would the "crush washer" be sized to fit over the BSP thread, or inside
the female?

thanks,
graham.


Parallel threads normally seal on a flange and face - with a fibre or
squashable copper washer in between. Does the male thread on the gauge
have a flange?

If not, you may get away with some liquid PTFE thread sealant, but
that's not ideal.

It seems depressingly common that random gauges come with BSPP threads. I
had one supplied with a water pressure regulator (so it wa not a case of the
wrong choice of base). There is no way it would reach down for a washer nor
was there a decent flat shoulder to seal on.

I used several turns of Gas PTFE until it was "very tight" then wound it in
to th eposition I wanted.

However, water is rather more forgiving than gas, so I think in the OP's
case I would use a vacuum approved (gas grade) thread sealant.

I assume this is only for soft vacuum work?


It's for a veneer press, so in the region of -750mBar (relative).
I don't know if that counts as "soft", though apparently it is a
"rough", "low" or "coarse" vacuum!

It does seem odd that nearly all the vacuum gauges in the uk are
parallel threads, whereas it's all NPT in the states - I'd have thought
a male + female tapered thread would be the ideal. otoh, if parallel is
so common it must work.

g

[Nightjar]

On 06/07/2013 20:14, graham wrote:
Nightjar wrote on 06/07/13 18:04:
On 06/07/2013 17:07, graham wrote:
I'm looking at buying a vacuum gauge, but they nearly all have BSPP
(male) threads - can anyone tell me how these are supposed to be sealed
when fitted to the BSPP female?
I've come across mention of copper crush washers and bonded washers, but
i've no idea if this is the standard technique.
Would the "crush washer" be sized to fit over the BSP thread, or inside
the female?

A bonded washer is intended to go over the male thread and to seal
between the faces of the two fittings. A crush washer is intended to fit
inside the female fitting and be crushed by the extended male thread
that pressure gauges have. That should allow you to get the gauge facing
the right way when tightening it down and still get a seal. I have no
idea whether vacuum gauges work the same way, as I have never needed
vacuum.

Colin Bignell



ahh, thanks. Does one need a special female fitting suitable for a small
crush washer or is t a standard shape of all female BSPP fittings?


I've never seen a female fitting where you can't use a crush washer, but
I couldn't swear that they don't exist.

Colin Bignell

[Nightjar]

On 06/07/2013 20:22, graham wrote:
....
It does seem odd that nearly all the vacuum gauges in the uk are
parallel threads, whereas it's all NPT in the states - I'd have thought
a male + female tapered thread would be the ideal. ...

There would be no guarantee that you could get the gauge facing the
right way with that arrangement.

Colin Bignell

[graham]

Nightjar wrote on 07/07/13 10:46:
On 06/07/2013 20:14, graham wrote:
Nightjar wrote on 06/07/13 18:04:
On 06/07/2013 17:07, graham wrote:
I'm looking at buying a vacuum gauge, but they nearly all have BSPP
(male) threads - can anyone tell me how these are supposed to be sealed
when fitted to the BSPP female?
I've come across mention of copper crush washers and bonded washers,
but
i've no idea if this is the standard technique.
Would the "crush washer" be sized to fit over the BSP thread, or inside
the female?

A bonded washer is intended to go over the male thread and to seal
between the faces of the two fittings. A crush washer is intended to fit
inside the female fitting and be crushed by the extended male thread
that pressure gauges have. That should allow you to get the gauge facing
the right way when tightening it down and still get a seal. I have no
idea whether vacuum gauges work the same way, as I have never needed
vacuum.

Colin Bignell



ahh, thanks. Does one need a special female fitting suitable for a small
crush washer or is t a standard shape of all female BSPP fittings?


I've never seen a female fitting where you can't use a crush washer, but
I couldn't swear that they don't exist.

Colin Bignell


I won't hold you to it then

graham.