Vintage Tire Pressure Gauge Calibration

Posted by Ryan Mar 14, 2023 at 12:56 PM and filed under Projects

Updated on Mar 14, 2023 at 12:56 PM

I’ve been collecting and using vintage tire pressure gauges since I can remember really… Mostly because I just really appreciate their aesthetic and the way they feel in my hand. Age brings a tactile feel and a personality that the newer offerings just can’t match.

Recently, I’ve been asked quite a few times about their accuracy. When you find them, they are hardly ever broken but it’s rare to find one that is accurate. Thankfully, however, most of these 1950’s to 1980’s gauges feature a very similar mechanism and calibrating them is dead easy.

So, I decided to make a little video hoping to save a few more gauges. If you are into such a thing, check it out:

View thread (34 replies)

bowbridge

Well-known member

Mar 14, 2023

How do you know that the gauge that you are calibrating the old gauges to is accurate?

Ryan

Administrator

Staff member

Mar 14, 2023

bowbridge said:
How do you know that the gauge that you are calibrating the old gauges to is accurate?

I have a pretty well regarded Jaco digital gauge that I compare them against. Close enough for the girls I go out with anyway…

engineer2

Well-known member

Mar 14, 2023

On a Bourdon tube pressure gauge there are three things to consider: Zero, linearity (around mid scale), and span (pressure at the max reading).
First thing to do is get "as found" readings at 0%, 25%, 50%, 75% and 100% of full scale.
It's difficult to say what the claimed accuracy originally might have been. Typically 2-3-2% (low, mid, high end), but super cheap might be ±5% of full scale.
Cheap digital gauges typically claim ±0.5% or ±1% FS accuracy.
Any gauge used for calibration should be at least 4 times more accurate than the gauge being calibrated.
Since you Jaco gauge claims to be ±0.5%, it should be fine to check any ±2% gauge.
Accuracy specs apply at room temperature and error increases at high or low temperatures.
Most of the inexpensive round digital gauges you see are made by the same companies in China. I've found them to be accurate enough for passenger car tires. Caution: They are not designed for liquids.

Back to Bourdon tube gauges.
Span is adjusted as you have described in your video, but may vary depending on who made the gauge.
Zero is often done by pulling the needle off and pressing it back on so it reads zero. It's usually best to use a needle pulling tool to avoid damaging the axle/gear mechanism. On these inexpensive gauges it might be difficult to tweak linearity.
If you set your tires to 30-32 psig for example, the main concerns would be zero and best calibration at 30 to 32 psig.

Last edited: Mar 14, 2023

Ryan

Administrator

Staff member

Mar 14, 2023

engineer2 said:
Back to Bourdon tube gauges.
Span is adjusted as you have described in your video, but may vary depending on who made the gauge.
Zero is often done by pulling the needle off and pressing it back on so it reads zero. It's usually best to use a needle pulling tool to avoid damaging the axle/gear mechanism. On these inexpensive gauge it might be difficult to tweak linearity.
If you set your tires to 30-32 psig for example, the main concerns would be zero and best calibration at 30 to 32 psig.

You are an engineer. I can tell. I like that.

So my tire pressure gauges are generally used in the 22 to 42 pound range on passenger car tires. When I set up one of these vintage dials in the way explained above, I might have a .5 pound difference in that range between the vintage gauge and my modern digital... And that's perfectly fine with me... and certainly better than a pencil gauge.

Sumboodie

Well-known member

Mar 14, 2023

bowbridge said:
How do you know that the gauge that you are calibrating the old gauges to is accurate?

Enter button get jammed?

I had to scroll 6 or 7 page lengths through that! Haha.

mercifiknow

Well-known member

Mar 14, 2023

engineer2 said:
On a Bourdon tube pressure gauge there are three things to consider: Zero, linearity (around mid scale), and span (pressure at the max reading).
First thing to do is get "as found" readings at 0%, 25%, 50%, 75% and 100% of full scale.
It's difficult to say what the claimed accuracy originally might have been. Typically 2-3-2% (low, mid, high end), but super cheap might be ±5% of full scale.
Cheap digital gauges typically claim ±0.5% or ±1% FS accuracy.
Any gauge used for calibration should be at least 4 times more accurate than the gauge being calibrated.
Since you Jaco gauge claims to be ±0.5%, it should be fine to check any ±2% gauge.
Accuracy specs apply at room temperature and error increases at high or low temperatures.
Most of the inexpensive round digital gauges you see are made by the same companies in China. I've found them to be accurate enough for passenger car tires. Caution: They are not designed for liquids.

Back to Bourdon tube gauges.
Span is adjusted as you have described in your video, but may vary depending on who made the gauge.
Zero is often done by pulling the needle off and pressing it back on so it reads zero. It's usually best to use a needle pulling tool to avoid damaging the axle/gear mechanism. On these inexpensive gauges it might be difficult to tweak linearity.
If you set your tires to 30-32 psig for example, the main concerns would be zero and best calibration at 30 to 32 psig.

I think I'm going to buy Bourdon's gauge. Terribly afraid of cheap imports from certain countries.

It's true...about the later...not the former. lol

The Cobbler

Super Moderator

Staff member

Mar 14, 2023

thanks for the tips!

Farmer J.

Well-known member

Mar 14, 2023

I check the accuracy of my gauge against the calibrated one in a professional tyre shop. It's local, and I know and trust them. Haven't needed to adjust my gauge, it's one of those circular old 'Made In USA' ones I got years ago and still reads correctly.

bigredcornhead

Well-known member

Mar 15, 2023

No one has asked yet lets see the collection, i have one that of the same vintage as the OP pic! I'll get a shot of it this evening to share!

Last edited: Mar 15, 2023

SteadyC

Well-known member

Mar 16, 2023

Or going off a known "good" mark gauge + or - X and no internal adjustments are necessary(If within span of desired measurement). Just connect regulated air to a manifold and check all gauges and mark accordingly.

Sumboodie

Well-known member

Mar 16, 2023

Most anything i have +- 20% wouldn't be a problem. More important that all 6 or 10 tires are close to equal pressure.

bbbarracuda

Well-known member

Mar 16, 2023

I never worry about how accurate any tire gauge is.
The important part is consistency.
Now, if the gauge reads 30 when it's actually 10.....

softailgarage

Well-known member

Mar 16, 2023

I have that exact pressure gauge and have had it since High School, 44 years. Its always been kept in a glovebox and I have yet had any problem with it, but maybe I should re-calibrate to be sure.

engineer2

Well-known member

Mar 17, 2023

I never worry about how accurate any tire gauge is.

Use a tread depth gauge to check for wear across your tires. As long as it is even, you are good to go.
Edge wear = underinflation or lots of cornering like a maniac.
Center wear = overinflation.

Ricky Joe

Well-known member

Mar 24, 2023

Very nice video. I wish they were all concise and informative, rather than the flowery, painfully tedious ones that take so long to even start to get to the point.

Here is the only dial one that I have.

HoosierBuddy

Well-known member

Mar 28, 2023

When you get tired of playing with those little old gauges, you can always step up to the big leagues.

So...I was compelled to restore this old thing. LONG/Pics

Gosh...the things I find myself spending (or perhaps wasting) time on. This is a Foxboro 2 pressure chart recorder, which I think was made in 1963. I was at work about a month ago when this thing came in from the field, covered in rust and full of spiders. A crew had gone out to mount some...

www.garagejournal.com

tool_scrounge

Well-known member

Mar 28, 2023

i had a job in College working around pumps and I spent a lot of my time calibrating gauges for pump testing. The two gold standard methods then were:

1) Dead weight tester. Imaging an instrument with a sealed oil reservoir and a piston pressing on it. you placed calibrated weights on the piston to generate a known accurate pressure. You took a data at a bunch of different pressures and generated a correction curve for that gauge.

2) For lower pressure gauges, we used a mercury manometer. Super accurate but the EPA would probably stroke out now having a gallon of mercury in your laboratory.

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Farmer J.

Well-known member

Mar 28, 2023

So that's how it's actually done, properly.. Thanks.

bowbridge

Well-known member

Mar 30, 2023

tool_scrounge said:
i had a job in College working around pumps and I spent a lot of my time calibrating gauges for pump testing. The two gold standard methods then were:

1) Dead weight tester. Imaging an instrument with a sealed oil reservoir and a piston pressing on it. you placed calibrated weights on the piston to generate a known accurate pressure. You took a data at a bunch of different pressures and generated a correction curve for that gauge.

2) For lower pressure gauges, we used a mercury manometer. Super accurate but the EPA would probably stroke out now having a gallon of mercury in your laboratory.

.

Very nice! I looked at the price of that piece of equipment, costs around $12,000 !! I'll have to wait until Harbor Freight comes out with one.

mogandave

Well-known member

Mar 30, 2023

23' of pvc vertical, full of water will give you 10 psi, and is pretty dang accurate.

tool_scrounge

Well-known member

Mar 30, 2023

mogandave said:
23' of pvc vertical, full of water will give you 10 psi, and is pretty dang accurate.

Yup, that is a water column manometer. We used Mercury as the density is 13.5x greater than water. So with an 8 foot column we could go up to around 40 psi.

tool_scrounge

Well-known member

Mar 30, 2023

bowbridge said:
Very nice! I looked at the price of that piece of equipment, costs around $12,000 !! I'll have to wait until Harbor Freight comes out with one.

You can find them on eBay used starting at around $500.

I had one for years. It was a really nice art deco cast iron design. I finally decided to part with it. A younger guy enthusiastically buys it the minute the ad appeared. He told me it was going to be displayed as the centerpiece of his living room. I asked him if he was single. He was surprised and confirmed he was single. He then asked how I knew? Err… “Lucky guess!” I answered.

Mike'smeatshop

Well-known member

Apr 8, 2023

Were these old Schrader's designed to be calibrated?

Citation

Well-known member

Apr 17, 2023

I have that same pressure gauge in my car (the cover page gauge). Funny to see it there.

Walkers

Well-known member

Apr 17, 2023

engineer2 said:
On a Bourdon tube pressure gauge there are three things to consider: Zero, linearity (around mid scale), and span (pressure at the max reading).
First thing to do is get "as found" readings at 0%, 25%, 50%, 75% and 100% of full scale.
It's difficult to say what the claimed accuracy originally might have been. Typically 2-3-2% (low, mid, high end), but super cheap might be ±5% of full scale.
Cheap digital gauges typically claim ±0.5% or ±1% FS accuracy.
Any gauge used for calibration should be at least 4 times more accurate than the gauge being calibrated.
Since you Jaco gauge claims to be ±0.5%, it should be fine to check any ±2% gauge.
Accuracy specs apply at room temperature and error increases at high or low temperatures.
Most of the inexpensive round digital gauges you see are made by the same companies in China. I've found them to be accurate enough for passenger car tires. Caution: They are not designed for liquids.

Back to Bourdon tube gauges.
Span is adjusted as you have described in your video, but may vary depending on who made the gauge.
Zero is often done by pulling the needle off and pressing it back on so it reads zero. It's usually best to use a needle pulling tool to avoid damaging the axle/gear mechanism. On these inexpensive gauges it might be difficult to tweak linearity.
If you set your tires to 30-32 psig for example, the main concerns would be zero and best calibration at 30 to 32 psig.

Oh yeah! I spent years calibrating my gauges once a quarter when I worked at the gas utility co. You get to be a master at playing with Bourdon tubes and linkages. Still, every once in a while one goes in the scrap bin after an hour or two of not being able to dial it in.

ericg

Well-known member

Apr 27, 2023

I was wondering if anyone could tell me the correct orientation of the conical spring, the plastic washer and the rubber washer of my Milton gauge. In addition, the gauge will not hold the reading. As soon as the hose is removed from the tire valve, the pressure drops to zero. Is there an internal check valve that is not functioning correctly? Any help would be appreciated

Last edited: Apr 27, 2023

gambo53

Member

Apr 30, 2023

My 100+ year old US Gauge Co NY for balloon or standard tires, Pat'd. June 13, 1911, Made in U.S.A. Chromed gauge with original leather storage bag. Still works great!

Dragfluid

ALLIANCE MEMBER

May 2, 2023

Many moons ago, I bought one exactly like what's in the Boss's pic up on top. Had it for years, then I don't know what happened to it.

Vtor

Well-known member

Sep 3, 2023

I have accu cage like OP, but white face and it also suffers from being too suffers from being 2-4 psi off at around 30psi, but if that is all you use for balancing front/rear pressure during competition.. its OK.

Was gifted a longacre w broken glass few years ago that i restored, so that's my go to now. I do miss the super compact nature of the accu-cage. Tuck in seat cushion.. off to the next run.

Jim Sperry

Well-known member

Oct 17, 2023

Beautiful to see their gauges still used. I used to have the calibration chart from Philip Parduhn at ghmeiser but it is no longer findable

GarageDan

Well-known member

Oct 17, 2023

I never knew how to calibrate these, thanks for sharing! Now... you say you had 20 of these in your collection... you can't say that and not share some pics!