Mechanical Air Pressure Gauges

Topic: Mechanical Air Pressure Gauges (Read 1142 times) previous topic - next topic

Mechanical Air Pressure Gauges

February 01, 2017, 10:38:16 pm

I have pulled together some messages from a classified listing (which will disappear after six months) and another thread. I want to further explore the concept of using mechanical air pressure gauges. My main interest is to be able to monitor the remaining air pressure in my front and rear air tanks.

Trent.

Quote from: Falconguy – January 18, 2017, 11:28:50 am

I recently changed my air pressure gauges to direct reading. These are the electric ones that were removed.

Quote from: TulsaTrent – January 18, 2017, 01:27:24 pm

By direct reading, do you mean mechanical, so they keep reading after the engine is turned off?

If so, which ones did you use?

Quote from: Falconguy – January 18, 2017, 03:40:01 pm

Yes, they read after the engine is shut down.

Replaced them with VDO units that look identical except they only say air and are a better scale.

Air Pressure | By Type | Instruments, Displays and Clusters | VDO Instruments...

Quote from: Roger & Susan in Home2 – November 23, 2016, 10:20:45 am

When your electronic air pressure gauges fail replace them with mechnical ones, much better since they show the pressure all the time even if the coach is off.

Re: Mechanical Air Pressure Gauges

Reply #1 – February 01, 2017, 11:09:10 pm

From the above messages, I conclude that my existing VDO air pressure gauges are electrical, not mechanical. To me, that means that mine have an electrical signal from some kind of transducer that sends an electrical signal to the VDO gauge display, while the power is supplied. When the engine is shut off, then the needle on the gauges, goes back to zero.

However, when I open the dash, I see an air hose going to the back of each air pressure gauge. I think they are classified as mechanical gauges by VDO. I did find a pair of VDO mechanical air pressure gauges that match the existing gauges, but one says Front, and one says Rear. They are about $60 each.

I do not want to buy them and replace my existing gauges, and find out that they, too, go to zero when the power is off.

Would someone who already researched this, and maybe already replaced theirs, please tell me what I am misunderstanding?

Thank you,

Trent

Re: Mechanical Air Pressure Gauges

Reply #2 – February 01, 2017, 11:53:50 pm

I changed my electronic gauges to the VDO Front/Rear mechanical gauges they continue to read air pressure after engine is shut down. A benefit in my view. Check the plumbing.

Re: Mechanical Air Pressure Gauges

Reply #3 – February 02, 2017, 12:06:47 am

Quote from: Roger & Susan in Home2 – February 01, 2017, 11:53:50 pm

I changed my electronic gauges to the VDO Front/Rear mechanical gauges

Roger,

Did your old gauges already have air hoses going to the back of them?

Trent

Re: Mechanical Air Pressure Gauges

Reply #4 – February 02, 2017, 09:21:21 am

Nope, the air tanks had transducers then wires to the gray(later blue) box then wires to all of the gauges from the gray box. Something unrepairable and unreplacable died in the gray box. I think the gauges are OK, it was something in the gray box. The new gauges are easier to read, much better lighting and show air pressure after you shut the engine off. My start battery voltage moves when you turn on the ignition but it no longer reads anything. I am going to replace it with another air pressure gauge connected to the HWH air tank.

150-112: Vision Black Air Pressure Gauge | VDO Gauges | eGauges.com
150-105: Vision Black Mechanical Engine Pressure Gauge | VDO Gauges |...
150-106: Vision Black Mechanical Engine Pressure Gauge | VDO Gauges |...

Re: Mechanical Air Pressure Gauges

Reply #5 – February 02, 2017, 10:08:04 am

I replaced mine to VDO as well. Much better but had to leave the old ones wire tied behind the dash or I think would set off the low air alarm

Re: Mechanical Air Pressure Gauges

Reply #6 – February 02, 2017, 10:22:26 am

Trent, mine have air lines going to them and they show pressure after ign is off, so what was changed as we are same year build?
JohnH

Re: Mechanical Air Pressure Gauges

Reply #7 – February 02, 2017, 10:41:09 am

Quote from: John Haygarth – February 02, 2017, 10:22:26 am

they show pressure after ign is off, so what was changed as we are same year build?

John,

Because of my plumbing and your description, it is probably just my memory. Mine does have some air leaks, which is why I have it up on stands. The fact that it doesn't show much air after a while may have convinced my almond-sized brain that it did not retain its setting. (I have wasted a LOT of time researching mechanical air pressure gauges. Will try to share that info with the forum.)

Trent

Re: Mechanical Air Pressure Gauges

Reply #8 – February 02, 2017, 10:46:17 am

The VDO gauges at less than $40 are pretty good, red, green or white lighting. My gauges do drop aftre a day or so the are down to 50 psi or so. After 10 days down to about 20 psi. I have a check valve leaking somehwere, nothing else seems to be leaking. Don't overcomplicate it.

I can live with it.

Re: Mechanical Air Pressure Gauges

Reply #9 – February 02, 2017, 11:34:28 am

If you just want to replace your existing electronic air pressure gauges with VDO mechanical air pressure gauges, The best price I have found is at O'reilly Auto Parts. They sell the VDO 150-307 for only $32.99 each. It has a chrome trim ring and a white pointer. The way they are mounted in our 2000 Foretravels, the chrome will not be visible. The only appearance difference will be the white pointer instead of a red pointer like the other dash gauges. (Actually might help recognize them in a scan of your gauges.)

http://www.oreillyauto.com/site/c/detail/VDO0/150307/N0827.oap?ck=Search_N0827_-1_3904&pt=N0827&ppt=C0134#itemDetailTab_

Trent

Re: Mechanical Air Pressure Gauges

Reply #10 – February 02, 2017, 11:34:54 am

My links go to the single unit prices, $35-39 each. Bulk is about $6 less.

Like John, I left the transducers and wires to the gray box. Low pressure alarm was dinging with or without the wires connected or the dead dead gauges hooked up. A 4-5 volt signal to the ding maker on that circuit should make it stop. Or like I did put in a switch to shut the dinger up. Added wiring from turn signal feeds from the smart wheel plug with some diodes to make it ding for the turn signals.

In the 2001 the chrome rings would show.

Re: Mechanical Air Pressure Gauges

Reply #11 – February 02, 2017, 11:39:29 am

Roger,

You are right; one of these days I am going to have to learn to read. I have removed my erroneous message.

Thanks,

Trent

Re: Mechanical Air Pressure Gauges

Reply #12 – February 02, 2017, 11:50:07 am

In all your remodel work don't forget you have a Low Air Alarm somewhere in your system, it must remain.

Re: Mechanical Air Pressure Gauges

Reply #13 – February 02, 2017, 03:43:18 pm

we have been parked here for 12 days and pressure is front 65 rear tank 55, and most of that loss is with the step cylinders which I have to address yet. other than that I am fine with this loss to date.
JohnH

Re: Mechanical Air Pressure Gauges

Reply #14 – February 02, 2017, 07:12:33 pm

John, I would love to have no air leaks, mine seem to be hard to track down but I am not too concerned about them. We get somewhere, level up, shut the HWH off and the little compressor off and we are still level two weeks later. Works for me.

Re: Mechanical Air Pressure Gauges

Reply #15 – February 02, 2017, 09:35:18 pm

Like I said Rog' I am happy too even with the loss I have now. I kow I can make it better and will do once those step cylinders are done but not a big deal.
JohnH

Re: Mechanical Air Pressure Gauges

Reply #16 – February 02, 2017, 10:55:00 pm

It would probably be easier if you knew someone with a pit!

Trent

Re: Mechanical Air Pressure Gauges

Reply #17 – December 26, 2021, 12:18:10 pm

Quote from: Roger & Susan in Home2 – February 02, 2017, 09:21:21 am

Nope, the air tanks had transducers then wires to the gray(later blue) box then wires to all of the gauges from the gray box.

Where does this box live? And do you know what years had the box vs. mechanical?

Re: Mechanical Air Pressure Gauges

Reply #18 – December 26, 2021, 12:41:35 pm

Quote from: Elliott – December 26, 2021, 12:18:10 pm

Where does this box live? And do you know what years had the box vs. mechanical?

On mine it is under dash cover to the left of the center of dash

Re: Mechanical Air Pressure Gauges

Reply #19 – December 26, 2021, 12:43:15 pm

Quote from: Roger & Susan in Home2 – February 02, 2017, 11:34:54 am

My links go to the single unit prices, $35-39 each. Bulk is about $6 less.

Like John, I left the transducers and wires to the gray box. Low pressure alarm was dinging with or without the wires connected or the dead dead gauges hooked up. A 4-5 volt signal to the ding maker on that circuit should make it stop. Or like I did put in a switch to shut the dinger up. Added wiring from turn signal feeds from the smart wheel plug with some diodes to make it ding for the turn signals.

In the 2001 the chrome rings would show.

Did you add diodes for oil pressure and engine fault indications or are they too silenced
DOT requires a low air pressure audible alert as I recall also
Scott

Re: Mechanical Air Pressure Gauges

Reply #20 – December 26, 2021, 12:45:02 pm

Elliot,
I think i remember reading something about a blue box behind the dash.
not sure if you can see it if you look up from the pedals.
I have a rear tank gauge thats pegged out, sometimes goes back to normal then back to pegged out. it's on my to do list someday.

Re: Mechanical Air Pressure Gauges

Reply #21 – December 26, 2021, 01:00:38 pm

Quote from: dsd – December 26, 2021, 12:43:15 pm

DOT requires a low air pressure audible alert as I recall...

Unless I am mistaken, DOT requires either audible OR visible warning signal, PLUS a functioning air pressure gauge.

"A warning signal that is audible or visible to a person in the normal driving position and provides a continuous warning to the driver whenever the air pressure in the service reservoir system is at (55 psi) and below, or one-half of the compressor governor cutout pressure, whichever is less."

https://www.govinfo.gov/content/pkg/CFR-2012-title49-vol5/pdf/CFR-2012-title49-vol5-sec393-51.pdf

Re: Mechanical Air Pressure Gauges

Reply #22 – December 26, 2021, 01:05:28 pm

Lift up the curved part of dash cover above the instrument panel and the blue box will be right there.

Re: Mechanical Air Pressure Gauges

Reply #23 – December 27, 2021, 10:08:45 am

Quote from: dsd – December 26, 2021, 12:43:15 pm

Did you add diodes for oil pressure and engine fault indications or are they too silenced
DOT requires a low air pressure audible alert as I recall also
Scott

Diodes in the left and right turn signal circuits allow the beeper to beep without any feedback from left to right or the other way. There is only one flasher that makes either flash and without isolating diodes to the beeper, turning on the turn signal, either way, would make all of the turn signals flash.

The blue (or in mine gray) boxes are not replaceable and not repairable. It provides the 5v signal to the pressure transducers and the return voltage indicated the level of pressure. Both of my electronic gauges quit reporting at the same time. There was no signal to the gauges from the gray box. And later I detected no 5v at the transducers. Some internal thing in the gray box detects know pressure from the transducer and sends a signal through a different set of wires to the dash warning light and another to the dinger. When mine failed the dinger dinged for 2 days until I got somewhere warm enough to dig into the dash and add a switch to the dinger.

As I recall there was a red light on the electronic gauge that was the warning light.

There are in-line low-pressure sensors that will trigger an alarm indicator, light, or noise. I have not added those.

We may be governed by these DOT rules but the motorhome is not a commercial vehicle and is not registered with the DOT.

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