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kgwilson

Oil Pressure off the scale

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Thanks jetboy. I have never noticed a second port , I'll have a look soon. There was a mod some years ago to change the oil pump to reduce pulsations which were causing oil filters to leak. Is this relevant?

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Will be the sender as pictured

I had one flicker and show falling pressure in cruise, ew sender all good

Orifice is to level out pressure pulses which Jabiru has heaps of

In the second port I have a normal low pressure switch and light on panel, gives comfort if gauge playing up

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If your aircraft is a 19 Rego, or similar, you might want to check out Speco gauges. Much cheaper than VDO. My Speco oil pressure indicator (gauge & sender) lasted well over 700 hrs (I have a conversation on this somewhere)

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I'll back Skippy on the Speco gauges, they're good, I've used them for many years on ground equipment applications.

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Thanks for the info. I have installed a new VDO sender and as I was given it for free it seems a good solution. If it fails I'll have a look at the Speco gauge.

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Posted (edited)

Bruce, there is a range of Speco fuel pressure gauges, but they all read 0-15psi. I have never personally come across a fuel pressure gauge that only reads 0-5psi.

 

The full range of Speco gauges is in the catalogue link below.

 

http://www.speco.com.au/Downloads/SpecoGaugeCatalogue2005b.pdf

Edited by Guest
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reading any pressure that low is difficult electrically and don't want a fuel tube coming inside either for a mechanical type ...…...

Whoever Dynon uses, Kavlico?? have one and measuring fuel pressure in Jab bounces around from 3.5 - 0 all the time

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reading any pressure that low is difficult electrically and don't want a fuel tube coming inside either for a mechanical type ...…...

Whoever Dynon uses, Kavlico?? have one and measuring fuel pressure in Jab bounces around from 3.5 - 0 all the time

 

Following your earlier comments - why not make up an "in line" fitting with a very small orifice. This is a pretty common way of reducing the effects of pulsing/fluctuations - may make the gauge a little slow to react however this is probably better than a needle jumping around.

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Whoever Dynon uses, Kavlico?? have one and measuring fuel pressure in Jab bounces around from 3.5 - 0 all the time

I was thinking about my small oil pressure fluctuations, especially at lower rpm (in a Rotax) and thought how great it would be if dynon added some sort of adjustable electronic buffer in their system to smooth out pulses and fluctuations....

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yes that's what we have in industrial signal conversion, averaging smooths this stuff out, can widen range on screen and these minor changes don't register as much but may as well not have it then

With the fuel pressure I think maybe its real pressure variation as float opens and closes, air in fuel lines also makes these variations worse, could be spring regulated mech pump working against float valve.

the pressure drop, and drops over ~5 sec then bounces back to high and drops again

No needle just coloured electrons bouncing around and they love it

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Posted (edited)

Float (with needle) operations are usually erratic, rather than steady. "play" in the linkage makes it worse. Nev

Edited by Guest

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There was a Jabiru directive about pressure fluctuations from the oil pump which caused oil coolers to leak. The gauge was not reacting to the high-frequency fluctuations and it needed an oscilloscope instrument to see them. Jabiru had to apologise to the oil-cooler makers. The fix was a small mod to the oil pump to prevent too sharp a valve closure.

I find it very possible that something like this could happen on the fuel side, but it would take more sophisticated instrumentation to see it than an ordinary gauge.

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I find it very possible that something like this could happen on the fuel side, but it would take more sophisticated instrumentation to see it than an ordinary gauge.

The fuel supply and metering systems are quite a bit different to the oil system.

A dedicated fuel pressure regulator would probably be the solution to any fluctuations and supply a steady pressure/flow.

Manufacturers don't obviously see the need and complexity but it would be interesting to try one.

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I'm not sure the supply side of it is the issue in the case of fuel. The actual float needle will operate in an irregular way when keeping the fule at (roughly) the correct level in the float bowl.

In an oil system both the pump and the relief valve could contribute to uneven pressure.. The pump is either a trochoid or a gear pump, generally and will probably be anything but silent if you put a stethoscope on a feed pipe.. Nev

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