Are all pressure gauges the same?
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  1. #1
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    Default Are all pressure gauges the same?

    As the title suggests, would a fuel pressure gauge register air pressure accurately?

    I notice most industrial type gauges state that they will work with oil/air/any fluid that will not corrode the device?

    I just need a simple small pressure gauge for boost (it doesn't need to be hyper accurate as it's not for setting boost, just for secondary indicator).

    There are several 1 1/2 fuel pressure gauges and industrial pressure gauges around but no 1-1/2 inch boost gauges...

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    COL
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    Default Pressure Guage

    Hi mistareno

    Yes it should work o.k.
    You will probably need a guage with a range of 0 to 20 PSI (0 to 140 KPa)
    Regards Col

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    1000+ Posts Frans's Avatar
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    Yes all are the same. They work by means of a Bourdon Tube. It is an oval tube bent in a halfmoon shape. With pressure inside they try to go straight, almost like these blow whistles kids have at parties where you blow into it and it rolls out.
    On the end of the tube is a linkage mechanism that activates a little rack and the needle have a pinion that deflects and give you the press. All pressures (water or air) deflect the same amount for the same pressure.
    Frans
    Old enough to know better
    Young enough to do it anyway.

  4. #4
    bob
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    G'day Richard,

    agree with the others, except that in our plastics age you may find active elements that are of the space age wonder material :-)

    Arrange your feed tube so that it naturally drains away from the gauge to get rid of any condensates that may cause you grief. Sometimes gauge feeds are arranged with a syphon in the tube with a "friendly" fluid in the syphon but you shouldn't need to go to that extent.

    cheers,
    Bob

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    Quote Originally Posted by COL View Post
    Hi mistareno

    Yes it should work o.k.
    You will probably need a gauge with a range of 0 to 20 PSI (0 to 140 KPa)
    Thanks for that, I had almost convinced myself that it would be okay, so thanks for the confirmation.

    I can get one gauge that is 0-15psi or another that is 0-30psi - I think the Fuego would have a meltdown if I tried putting anywhere near 30psi through it so I should be safe with the 15psi version

    This is the 30psi gauge -

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    Richard

    At one stage I was offered half a trailer load of aircraft boost gauges to sell on behalf of Hughes Trading that was then located in Sydney Road. I took some of them to Bendigo swap meet to try and sell, but found no interest at all from buyers, so returned them to Hughes trading. Bill Hughes relocated to the Kyneton area and for a while operated a disposal place in one of the main streets.

    I have the feeling that Bill may have passed on, as a few years later a lot of his old aircraft and motor vehicle stock was being sold at Bendigo swap meet.

    As you know the Kyneton area well, you may be able to locate the family, they had a property near Kyneton with a large shed and relocated a lot of stock there as the Coburg business was wound down, they may still have lots of unusual items including some of the boost gauges etc.

    Ken

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    Quote Originally Posted by Kenfuego View Post
    Richard

    At one stage I was offered half a trailer load of aircraft boost gauges to sell on behalf of Hughes Trading that was then located in Sydney Road. I took some of them to Bendigo swap meet to try and sell, but found no interest at all from buyers, so returned them to Hughes trading. Bill Hughes relocated to the Kyneton area and for a while operated a disposal place in one of the main streets.

    I have the feeling that Bill may have passed on, as a few years later a lot of his old aircraft and motor vehicle stock was being sold at Bendigo swap meet.

    As you know the Kyneton area well, you may be able to locate the family, they had a property near Kyneton with a large shed and relocated a lot of stock there as the Coburg business was wound down, they may still have lots of unusual items including some of the boost gauges etc.

    Ken
    Thanks Ken, that might come in handy.

    I'm using the smaller 40mm gauges so I can hopefully fit 2 gauges a shift light and a couple of warning LED's all on a pod attached to the top of the steering column.

    With 40mm gauges (1-1/2") I will still get a good view of everything on the dash except the oil level gauge (that I don't really use anyway) and all the info will be in close clear view which should make up for the fact that the gauges are small.

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    COL
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    Default Pressure Guage

    Hi mistareno

    If you are only running low boost like 7 PSI a 0 to 15 PSI guage would be fine
    Regards Col

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    Quote Originally Posted by COL View Post
    Hi mistareno

    If you are only running low boost like 7 PSI a 0 to 15 PSI guage would be fine
    Yeah, 15 psi would be the absolute outer limits of boost for what I have planned.

    At least with the 15psi gauge, it will probably be using a fair portion of the gauge sweep which should make it a bit more accurate / easier to read at a glance.

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    COL
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    Default Pressure Guage

    Quote Originally Posted by mistareno View Post
    Yeah, 15 psi would be the absolute outer limits of boost for what I have planned.

    At least with the 15psi gauge, it will probably be using a fair portion of the gauge sweep which should make it a bit more accurate / easier to read at a glance.
    Yep that is correct
    Regards Col

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  11. #11
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    mistareno,

    One issue to keep in mind when using gauges sourced from wherever is that gauges are calibrated in two standards - Gauge or Absolute pressures.

    Gauge calibration starts from zero (at mean sea level), but Absolute starts from 14.7 PSI. If you select an instrument from any source you may pick up either of the two. If the latter it will read nearly 15 PSI with no input at sea level, but it may also be far more accurate than the alternative over its range. Any attempt to reset the pointer to zero will stuff up the accuracy of the instrument.

    Regards,

    fento

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    Quote Originally Posted by fento View Post
    mistareno,

    One issue to keep in mind when using gauges sourced from wherever is that gauges are calibrated in two standards - Gauge or Absolute pressures.

    Gauge calibration starts from zero (at mean sea level), but Absolute starts from 14.7 PSI. If you select an instrument from any source you may pick up either of the two. If the latter it will read nearly 15 PSI with no input at sea level, but it may also be far more accurate than the alternative over its range. Any attempt to reset the pointer to zero will stuff up the accuracy of the instrument.

    Regards,

    fento
    The gauges I have been looking at have a needle pointing at zero, so I assume they would be the simple gauge calibration type.

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    Maybe a bit "over the top" but I would not recommend using a mechanical boost gauge located in the cabin of the car. If you do, use quality hose and fittings to avoid leaks or hose blowing off, due to the possibility of injecting flammable air mixture into the car.

    An alternative, and I think used on production vehicles, is an electrical gauge operated by a sensor in the manifold, which avoids any physical possibilty of gas in the cab.

    Just a thought.
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    WLB
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    Quote Originally Posted by mistareno View Post
    Yeah, 15 psi would be the absolute outer limits of boost for what I have planned.

    At least with the 15psi gauge, it will probably be using a fair portion of the gauge sweep which should make it a bit more accurate / easier to read at a glance.
    In that case you will need one with a bigger scale. A Bourdon tube gauge should only be operated to ideally 2/3 of its scale and worst case 3/4. Otherwise the tube becomes stretched or distorted and you lose accuracy and the needle may end up not returning to zero. If you need greater reading accuracy, you choose a larger dial face.

    If due to boost control valves, waste-gates, etc. you ever see sudden changes in pressure then you need to fit a snubber to the gauge. This is a fitting that screws onto the inlet nipple of the gauge and contains a scintered filter or tiny orifice. These restrict gas flow and slow down the response of the needle. Without a snubber, sudden pressure changes can damage the Bourdon tube or cause the needle pinion gear to jump some teeth on the rack. This then throws the calibration out and the needle doesn't return to zero. Industrial gauges sometimes go one step further and the body of the gauge is sealed and filled with clear oil to cushion internal movement.

    If the turbo is pushing through the fuel injection body or carby and you tap your pressure before fuel is admitted, there is obviously no need to worry about petrol vapour being blown into the cabin if the hose leaks or comes off. But if it taps in after fuel is admitted, then it's a real hazard as Fordman has described. But this can also be overcome using another common industrial component. A fitting containing a diaphragm is installed at or near the tapping point and the tube between it and the gauge is filled with a light oil - often silicone oil. The air pressure moves the diaphragm and the pressure is transferred to the incompressible oil which operates the pressure gauge.

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