Recalibrating old Boiler Gauges?

Hot_n_Cold

Another silly late-night thought...
I took an old Winters Boiler Pressure Gauge from a melted boiler, decided to open it up. I noticed some springs and gears... at atmospheric, it would read -10vac... I found that I could press on the spring and actually kinda recalibrate the baseline near 0. It says "Internal Syphon"
I have no clue how this thing works, but I really want to understand it. I'd love to learn more about this old type of gauge and if there's any possibility of repurposing it. (I love tinkering with old broken things)

Pumpguy

That's a bourdon tube compound gauge measuring to 30" Hg. on the vacuum side and 15 PSI on the pressure side.

The bourdon tube flexes as the pressure changes. The linkage at the end of the bourdon tube is connected to the gauge's needle to indicate the pressure.

I have no idea what the purpose is of that flat brass coil spring.

Sometimes when resting at atmospheric pressure the needle is not quite at the zero. If that's the case, the needle is usually a friction fit on its pivot, so tweaking it a little so it rests at zero will bring everything in line.

Jamie Hall

And just to add to @Pumpguy 's comment, the things are about as close to bulletproof as a gauge can be. So long as they have never been seriously overpressured, all they need is to be rezeroed from time to time.

Hot_n_Cold

Jamie Hall said:

And just to add to @Pumpguy 's comment, the things are about as close to bulletproof as a gauge can be. So long as they have never been seriously overpressured, all they need is to be rezeroed from time to time.

This one was on a boiler that melted down because of LWCO failure. Was pretty bad.
Any hope for it? lol

Pumpguy said:

That's a bourdon tube compound gauge measuring to 30" Hg. on the vacuum side and 15 PSI on the pressure side.

The bourdon tube flexes as the pressure changes. The linkage at the end of the bourdon tube is connected to the gauge's needle to indicate the pressure.

I have no idea what the purpose is of that flat brass coil spring.

Sometimes when resting at atmospheric pressure the needle is not quite at the zero. If that's the case, the needle is usually a friction fit on its pivot, so tweaking it a little so it rests at zero will bring everything in line.

Bourdon tube?
I noticed it seems like there's 2 somewhat seperate metals in the 1/8" male thread pipe that would screw into the boiler. But it seems like they're kinda welded together...
This one boggles my mind...

PRR

Bourdon tube--- if you bend a tube, then apply pressure, it straightens out like a limp balloon going stiff. It's really about the metal elasticity and dimensions, so pretty darn stable. Yes, the Zero likes to shift, and is trivially changed. (Squeeze/pry the J-arm.)
You also need a reading at a Known Pressure to check the proportionality. If that is wrong, you could make the tube longer or shorter or flatter/fatter; really easier to re-mark the numbers.
I think the fine hair-spring just takes-up the slop in the gears, for consistency and so it don't look jerky.

Jamie Hall

"This one was on a boiler that melted down because of LWCO failure. Was pretty bad.
Any hope for it? lol"

No problem. The abuse which can kill them is enough pressure to distort the bourdon tube or break the gears. And that's at least twice the rated pressure -- which is usually at least twice the maximum scale reading. That one looks OK.

Sylvain

Hot_n_Cold said:

I have no clue how this thing works, but I really want to understand it.

Put a garden hose coiled on the ground with the faucet closed (the other end must be open such that there is no pressure trapped in it). Then open the faucet. You will see the hose will try to straighten itself.
That is how it works.

Rezeroing and calibrating are two differents things.
For calibration you will need a precise and accurate reference gauge for comparison. Then you can write down, a calibration chart.

PRR said:

I think the fine hair-spring just takes-up the slop.

I agree

Pumpguy

I have a 20 ton capacity hydraulic shop press I use for pressing shafts out of pump rotors, and similar press work. The hydraulic ram has a 14000 PSI pressure gauge and the H frame is of rather light construction.

When I have something that's a bit stubborn, the H frame flexes as the pressure builds until there's enough to move the shaft with a loud BOING!. Now the pressure gauge is showing 200 PSI with no pressure.

I think I need a shockproof gauge.

SteamingatMohawk

Would a pressure gauge snubber work? Pressure could be kinda high.

Pumpguy

SteamingatMohawk said:

Would a pressure gauge snubber work? Pressure could be kinda high.

Maybe..... The threads are a strange form so connecting could be problematic. I just use the gauge as a rough indicator anyway. I'm not concerned about actual pressure.