Miniature pressure gauges

[Anonymous]

Posted by JasonB on 16/01/2017 13:26:18:

Who is up for the challenge?

Not me, I've got a traction engine to build. And if you believe that you'll believe anything!

Andrew

[JasonBModerator @jasonb]

So being the awkward sod squad that you are you won't be tempted to use the simple link and pivot innards like Henry's article in ME in preference to gears. I assume the geared ones have the needle pivot in the centre of the dial and it needs to move in a larger circle than the type where the needle pivots at the bottom of the dial and only needs to swing 45-60degrees?.

Out of interest what is the WP of your boiler?

J

PS for anyone tempted this is the ME issue

Edited By JasonB on 16/01/2017 14:29:34

[Anonymous]

Posted by JasonB on 16/01/2017 14:19:31:

So being the awkward sod ………………..

I've been called a lot worse than that, even on this forum!

A simple link won't work. By placing the link closer to the pivot of the pointer you can reduce the 'linear' movement required, but it still needs to move over the same angular rotation as the pointer. So if I want the pointer to move over 270° then the link also needs to move over 270°. If you think of a basic crank and rod you simply can't get that movement with a pull in one direction. Theoretically the best you can do is 180°.

I think many commercial pressure gauges have a central pointer with a 270° scale for better resolution. An alternative to gearing is to make the Bourdon tube in the form of a helix which terminates at the centre. As the Bourdon tube comes under pressure the termination point just rotates, in theory. For a given pressure the angular movement of a Bourdon tube is proportional to the total angle of the un-pressurised tube. So if you have multiple turns then you get a much bigger angular movement that the classic C shape. I did consider making a helical Bourdon tube, but decided it was going to be rather tricky. And since there are no adjustable linkages it would be difficult to calibrate.

The working pressure of my boilers is 170psi.

Andrew

[Gordon WParticipant @gordonw]

This may be off course– I remember taking a pressure gauge apart once and the drive to the pointer was rack and pinion. 'fraid that's all I can remember.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 16/01/2017 13:26:18:

And just to derail the thread further I was looking at an old ME yesterday and there was a write up on a Bourdon Engine. Used a Bourdon tube as a single acting "piston" with one end connected to the conrod, the other to a simple valve to fill or empty the tube.

Who is up for the challenge?

J

.

Would you care to share that article, Jason ?

Oops … I posted my response before finishing reading the thread 

… Sounds very interesting [even from this armchair perspective]

MichaelG.

Edited By Michael Gilligan on 16/01/2017 16:25:01

[Neil WyattModerator @neilwyatt]

Posted by Gordon W on 16/01/2017 16:06:53:

This may be off course– I remember taking a pressure gauge apart once and the drive to the pointer was rack and pinion. 'fraid that's all I can remember.

My original Bourdon dual gauge has rack and pinion :

So does the movement I have that would fit a 4" diameter gauge.

Neil

[Michael GilliganParticipant @michaelgilligan61133]

Andrew,

This may be daft [quite likely, given my premature reply to Jason] but: A fine thread wrapped around the arbor of the indicator might provide the requisite 'gearing' … without resorting to gears !!

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 16/01/2017 16:25:39:

My original Bourdon dual gauge has rack and pinion :

.

With respect, Mr Editor … That is not a rack; it's a sector of a circle.

MichaelG.

[JasonBModerator @jasonb]

Though often refered to as a quadrant and pinion even though the "rack" part may be more or less than a quater of the circle.

Andrew I can see your need for gearing of some sort if you need the needle to swing a 270degree arc

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Gilligan on 16/01/2017 16:39:18:

With respect, Mr Editor … That is not a rack; it's a sector of a circle.

.

… and to fend-off any pedantry, I should add "of finite radius"

MichaelG.

[Ray HulockParticipant @rayhulock43360]

Posted by John Alexander Stewart on 14/01/2017 02:49:28:

Hi Julian;

Here you go – the pressure gauge build is in Kozo Hiraoka's Climax book, back pages. I think it's also described in his Heisler book (in inches) and, probably in Live Steam magazine.

I do have the ME articles in my files – all are good designs, by master craftsmen – but what Kozo Hiraoka brings to the table is a clear description of the manufacturing process that lets those like me follow along.

Camden sells the Kozo books – here's a link to the Climax book:

**LINK**

A bit expensive, but, IIRC maybe the Heisler book was advertised as for sale on this site recently??

All fun stuff – JohnS.

You could be referring to the Climax book I advertised on here quite a few months ago and, as you say, it describes in detail how to form the Bowden tube etc.

Someone responded to my ad. almost immediately but later changed his mind so I just put it back in the bookcase. Still available if anyone wants it (mint condition) @ 25gbp + post at cost.

Ray.

[Michael GilliganParticipant @michaelgilligan61133]

For anyone who wants to develop the Bourdon Engine design:

Here is a slightly tidier copy of the drawing in the PDF

.

Draughtsmen … Start your CAD packages

MichaelG.

[JasonBModerator @jasonb]

I have sourced my Bourdon tube already

[Neil WyattModerator @neilwyatt]

Posted by Michael Gilligan on 16/01/2017 16:39:18:

Posted by Neil Wyatt on 16/01/2017 16:25:39:

My original Bourdon dual gauge has rack and pinion :

.

With respect, Mr Editor … That is not a rack; it's a sector of a circle.

MichaelG.

I knew you would say that before I even revisited this thread…

Neil

[Neil WyattModerator @neilwyatt]

Posted by Michael Gilligan on 16/01/2017 18:18:56:

For anyone who wants to develop the Bourdon Engine design:

Here is a slightly tidier copy of the drawing in the PDF

.

Draughtsmen … Start your CAD packages

MichaelG.

There was a letter about an example of the above design in issue 3573 of 1977 and and up to date design in 4200 of 2003 by Colin Andrews.

Neil

[Neil WyattModerator @neilwyatt]

Posted by JasonB on 16/01/2017 18:31:21:

I have sourced my Bourdon tube already

Do you have the joke and hat to go with it?

N.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 16/01/2017 18:31:39:

I knew you would say that before I even revisited this thread…

.

Pity you didn't spot it before you posted

MichaelG.

[JasonBModerator @jasonb]

From ME 4200

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 16/01/2017 18:38:13:

There was a letter about an example of the above design in issue 3573 of 1977 and and up to date design in 4200 of 2003 by Colin Andrews.

.

Oh well … probably not worth bothering then.

MichaelG.

.

Edit: Just found this interesting variation on the theme:

http://www.old-print.com/mas_assets/full2/J0261868/J0261868138.jpg

Edit: I think Ian SC might have beaten me to it in a previous thread:

http://www.model-engineer.co.uk/forums/postings.asp?th=101682&p=2

Edited By Michael Gilligan on 16/01/2017 20:35:38

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by Andrew Johnston on 16/01/2017 13:46:58:

Thanks for the gear cutter links and ideas. PPThornton list cutters down to 0.1mod, but I'm pretty sure they're all cycloidal form, for use in clocks.

What's the problem with cycloidal gears? They are typically used in clocks, as you say, where they are used for large wheels driving small pinions with low friction. I would have thought that is exactly what you want. Am I missing something?

Russell;

[Anonymous]

But they're not tolerant of centre to centre variations, which I may need to adjust to reduce backlash.

Andrew

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Andrew Johnston on 18/01/2017 09:16:22:

But they're not tolerant of centre to centre variations, which I may need to adjust to reduce backlash.

.

Please correct me if I'm wrong, Andrew … but, I presumed the mechanism would be spring-loaded.

MichaelG.

.

Edit: maybe something like this: https://goo.gl/images/4JwKuN

Edited By Michael Gilligan on 18/01/2017 09:33:30

[paul rushmerParticipant @paulrushmer83015]

Is there not normally a hair spring around the needle spindle to keep the backlash all one way?

Paul

[Ian S CParticipant @iansc]

There's nothing new in this world, this is Bourdon's improved steam or compressed air engine. Built byM Eugene Bourdon, of Paris. illistrated in "English Mechanic and Mirror of Science" Sept 4th 1868.

Ian S C

[Neil WyattModerator @neilwyatt]

Posted by Ian S C on 18/01/2017 11:07:54:

There's nothing new in this world, this is Bourdon's improved steam or compressed air engine. Built byM Eugene Bourdon, of Paris. illistrated in "English Mechanic and Mirror of Science" Sept 4th 1868.

Ian S C

Exactly

That's an updated version of the one picture earlier 😛

Neil

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