Adjustment of an old brass steam gauge?

I have "adjusted" several gauges by dropping them. I can't say that I would recommend this method.

CarlBoyd

All of the gauges I've adjusted (deliberately ) have followed the same pattern.

1) you cannot "calibrate" most bourdon-tube gauges, except at a single pressure -- that may be why it's 25psi off, or maybe not. The spring quality of the tube is usually the only spring element, and its tension is not readily adjustable. IF it has a separate balancing spring, there may be room for doing some range adjustments. 2) you rotate the hand on the shaft to calibrate it. Sometimes that involves loosening a hold-down screw that penetrates the hand; sometimes the hand is held on by friction.

It almost always involves holding the pinion behind the face with some sort of grasping tool so as not to over-stress the rack assembly.

LLoyd

Lloyd, I just called Ashcroft, and they have someone who knows how to support old brass gauges. (!)

That guy told me how to do it:

1) Put a little penetrating oil between the arrow hub and the shaft 2) Wait 1 day 3) Pull off the arrow carefully 4) Reinsert it at proper adjustment.

We did talk about linearity. At this point, it does not appear to me that it has a linearity problem, but I will double check with a notepad.

I've seen a number of gauges with a tiny pinion tool to adjust the needle, usually on higher end calibration gauges. The pinion has a pilot which engages a hole in the needle, with the gear engaging a gear on the retaining nut. I can't make out anything like that on your gauge, but there does appear to be some sort of nut. The first thing would be to determine how to get access to the front of the gauge. Does the bezel screw off?

Pete Keillor

Is it possible the gauge is not calibrated in PSI? I have a similar gauge and it reads in "feet of water" feet of water * 0.4335 =3D PSI.

40 feet* 0.4335=3D17.3 psi 40psi?-17.3psi=3D22.7psi (approximately 25)

Cool gauge either way. Good luck, Andy

--Next time you have a gauge you want to test you might want to build one of these:

I've found it to be tremendously useful and I take it on 'road trips' to steam events so's others can check their gauges.

"Ignoramus27827" wrote: ( clip) That guy told me how to do it: clip) 3) Pull off the arrow carefully (clip) ^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^ There are pullers for this job. If you don't have one, can't find one or don't want to buy one, you could make it. Attach a couple of hooks to a nut. Grind down a screw to go in the nut that fits into the hole in the hand-hub.

Yes, the guy told me that there are pullers for this. I will make something along the lines that you suggest. Will weld something during the TIG class tomorrow.

i >

Not to discount the other excellent ideas, but often times gauges displaying this kind of behavior have simply been spiked. When they are, the pinion has ran off the end of the rack and skipped one or more teeth. It's necessary to reset the pinion, or you loose reference to any springs in the mechanism.

Carefully see if you can gently wind the pinion to the end of the rack, and reset it. It might be helpful to pressure the gauge almost to the limit while you work on it, to avoid unnecessary stress on the components while you do so.

Can't be certain, but something else you might consider.

What do you mean by spiked?

I guess I do not really know how these gauges are build, so I cannot quite visualize what you say, but I think that I have some idea.

Either gauge has seen a pressure large enough that not only did the needle reach, it exceeded full-scale,

-or- the pressure to the gauge didn't exceed the gauge's max pressure, but the pressure ramped up so quick that once all the bits were moving, momentum carried the pieces beyond the applied pressure and their normal range.

Dave

"Ignoramus27827" wrote: What do you mean by spiked? ^^^^^^^^^^^^^^^^^^^^ The bourdon tube has a curved rack at the end, (a part of a gear) which is meshed to a pinion on the needle shaft, If the gauge is over-pressured, it is possible for the pinion to rotate past the proper mesh by clicking on the last tooth of the rack, sort of like a ratchet. It may be that one tooth produces a 25 psi error--or maybe 2 teeth, or n teeth. This would produce the kind of "suppressed zero" and constant error you are seeing.

That's probably what Eliot means by "spiked." This is a very good comment. If you rotate the needle slightly past full scale with your finger you will start to get clicks. If you do this carefully, one click at a time, you may be able to reset it without pulling the needle.

Exactly.

Iggy, once you have removed the cover it will become clear. By carefully exercising the gauge, and examine the design, you should be able to tell if over pressuring the gauge COULD cause this. You can also count the pinion teeth and compare it to the face, and see if one tooth might cause a 25 psi error. You can also consider the direction of rotation of the pinion as pressure increases, and consider of over pressure would cause a plus, or minus error.

If the answer to these questions are all, YES. Then I would bet that is the problem. Further, most gauges have a very gentle spring that needs to stay in sync with it's overall calibration. If this is the problem, and you correct it by removing and remounting the needle, it could forever affect accuracy. Also, depending on the gauge and your level of caution, it might be easier and less risky to reset the pinion as well.

More than anything be EXTREMELY gentle. Bending an of the components can be instantly fatal. Treat it like a live butterfly.

Seems like a very easy thing to try, and it makes sense. Thanks

"Elliot G" wrote: (clip) You can also consider the direction of rotation of the pinion as

^^^^^^^^^^^^^^^^^^^^ I think you can reason this out, and it I think it will. If you imagine the gauge reaching and exceeding full scale, so that the sector moves, while the pinion clicks, you are bringing the pinion to an engagement that's closer to the start of the sector. So, as the moves back toward zero, it will hit the stop pin before the pressure is completely gone. Thus, it will take some amount of pressure (maybe 25 psi) to start to move the needle upscale.

I fixed it, it works great now, all the way from 0 to 140 PSI.

i