What's with them? The lowest scale I can find is 0-15 psi, and I have one of those. Is that the lowest practical size to use a Bourdon tube?

I mounted it to the dash of the ol' brass picup today, and the electric fuel pump puts out only 1.5 psi. It's nonsensical to have a 0-15 gauge for that.

The only lower pressure gauges I could find are at McMaster.com for $60 and up, and they are fugly. Summit Racing has 0-15 gauges for $10.

I want to measure fuel pressure from my new exhaust pressure setup, and I expect it to hover around half a psi or less.

rdr

Why measure it Ralph? Isn't the exhaust pressure going to be so predictable that you don't need to?

In love with gauges or something.....?

Seth

No, Seth I try to keep the T uncluttered; no sidelamps, no carbide tank, etc. . I can use the temporary gauge I have now to learn the traits of my setup, but I'm likely to tinker quite awhile.

I'm as interested in the lack of 0-5 gauges as anything.

rdr

Ralph,

McMaster-Carr has a 0-3 psi gauge (4026K2)
for about $40.

Be_Zero_Be

I have (IIRC) a 0-5psi gauge. It's on a carb tester for checking the pop-off pressure of needle seats so I know they're made. I just don't think you'll find one that's "dash compatible" as far as bezel-beauty or mounting compatibility. Another application for low pressure gauges is fan testing. I forget the scientific name but they're out there--Possibly in the HVAC industry.

Side note, not to hijack the thread, but:

Was working in an aircraft shop long ago. A Continental powered aircraft came in with a heck of a lot of blowby on one engine. Upon contacting the Continental rep. we were told to find a plug on the engine and attach tubing to run into the cabin and hook up an airspeed indicator! It seems they'd found when the propeller shaft seal leaked it would pressurize the crankcase with air, shoving oil out the breather. One would think that a leaking prop shaft seal would've resulted in an oily engine, but no; the air pressure inside the nacelle was high enough to force air into the engine rather than letting oil out. Weird!

Back to the thread:

I guess an ASI would provide some indication of very low pressure, but I have no idea what the conversion from Pitot tube pressure to PSI would be.

Thanks, B0B. Dunno where you got the $40, but it's $53 plus shipping and tax online. Besides that, it's bottom feed, and 2 1/2", too big for a permanent install in a T. I'd like 1 1/2" like I have in a 0-60 for EFI, or smaller.

Interesting, John. I used an old manifold pressure gauge to measure exhaust backpressure in my 914 with new CAT, back before life in a T. I have some ASI around, too, but they'e all 3 1/8". 1" Hg is something like 146 mph.

Keep the ideas coming, please.
rdr

Bob, your catalog must be old. That number show $54+ now. But... Mc-C also has oz/in gauges too. A 0-60 in 1 ounce increments would seem to be a fairly accurate gauge for testing. (0-3.75psi)

Hi Ralph, keep looking! I found a NICE 4 lbs gauge that says "gasoline pressure" at Bakersfield for $25.00!

Ralph, I bought one for $20 that is zero to five pounds for #22, at Grainger on the West side of Long Beach. It has a modern plastic bezel but if you get a busted up old Sears and Roebuck Vacuum guage the cover for it fits and looks old. Just trade the front covers and you are in the game and it looks old . . . . Look at the picture below.

OK - OK - OK

My McM-C catalog is vintage, (#108) but, I never used to be older !

Be_Zero_Be

Hmmm, I think I've come up with a true T era fuel pressure gauge. Take a sight gauge like this 1U929 from Grainger:


Plumb the top port to a small sealed air tank, and feed the pressurized fuel at the bottom. The size of the tank, vs. volume in sight gauge will determine the pressure scale.

Here's what I have now:


rdr

Ralph,

I believe that "tank" you are talking about connected to the top port won't be necessary at all. If you just seal the top port, I think you'll have what you are looking for. True that not all of the gauge will be used at 1/2-1 psi.

Seth

You might find a gauge that reads in inches of water that has the resolution you are looking for. 0-60 inches of water maybe? 1.5 psi is something like 45 inches of water.

Be aware that the gauges that read in inches are generally a diaphram type guage. Make sure the diaphram material is good for gasoline vapor.

I have seen several oil gages from old Dodge Brothers cars at swap meets. They go to 6lbs.
They work greak for fuel pressure and have that period look.

There was one of those on my Speedster when I bought it and thought it was in ones not tens, So I put in one and a half pounds and popped the tank because it was actually 15 pounds. So I had the tank fixed and got a zero to five pound gauge. One and a half pounds on that little gauge is hard to see and is actually the thickbness of the needle over the zero mark. I also have a pressure relief valve because the hot direct sun can build the tank pressure up too high even on cool day.

Thanks for all the inputs, guys, and thanks especially for the caution about the diaphragms. As I wrote this morning, I am proceeding with a sight gauge for a fuel pressure gauge. I found a copper canister in my junk to use for the accumulator, and the way I have it figured, the gauge will be self-calibrating. I'll show pix when it's assembled.

I've ordered parts from McM, which will arrive Monday. Sure hope I get outbid on the gauges on Tbay I'm winning. If you're interested in them:
http://cgi.ebay.com:80/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=110380235437&ss PageName=ADME:B:BCA:MOTORS:1123

and the seller has two others that I bid $9 on.

rdr

The diaphragms are usually brass or bronze just like the Bourdon tube. Don't see how that makes a difference.

How about an altimeter? Pretty sensitive to low pressure changes. That is, Zero to 1000 ft. is a change of 0.52 psi.

Good thought, Terrence. I have some old altimeters lying around, and they would be ok for a temporary install.

I need to get back on the project, as it's almost completed. I don't know the pressure, but I am getting low oxygen ullage into the tank, so getting some safety benefit.

rdr

We have often used low range antique oil pressure gages for fuel pressure gages. The face detail is easily changed from drab to magnificent. Words like Frontenac, Rajo, Paco, etc. may be used. We probably should do a "How To" presentation on this subject. Larry Young, aka "Cam Man" is the expert on this.

One psi is 2.3 inches of water. Go the hardware store and get some clear plastic tubing, and yardstick. Use these materials and a little bit of water to make a manometer. You could mount them on wood panel and make them pretty if you wished. It would be more accurate than any gage.

Some great information in this thread! I'm off to Grainger's. Now if they only made a 0-3k RPM tach that I could put an antique face on...

Got to thinking about it, and I have some old airspeed indicators, too, and 1" of mercury equals 146 mph or so, and they are not so delicate as altimeters.

Reminded by the renewal of this thread, I did some more work on the setup this afternoon. I'm getting enough exhaust pressure to keep the gas tank aired up, but not enough to feed the high mounted carb through the electric fuel pump when it's not powered.

rdr

Hmmm - which is heavier - a pound of water or a pound of mercury???
But seriously ....
One Lb. per sq. inch = 2.036 inches of mercury or 27.70 inches of water.