Oil Pressure Sender

[builderflyer]

the question from ;Art,,,,Sonex taildragger #95,,,Jabiru 3300 #261
is ;I had looked for a pinhole coupling ??????
a may be answer to the question is """Wicks aircraft supply""" part #ea22r-o,,,,,,,restrictor fitting 1/8npt ,,orifice size .040
....good day / rick

Good find, Rick.........that's what I was searching for..........thanks.

Art,,,,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,Jabiru 3300 #261

[lpaaruule]

Here’s another source. You can chose brass or stainless steel. Many orifice sizes to choose from too. I may buy a smaller orifice and drill bigger if needed.

https://www.mcmaster.com/orifice-fittin ... -type~npt/

Edit: I bought the Stainless Steel one with the 0.01" orifice, and installed it last night. During a ground run the pressure was very stable, and appears to still allow the pressure reading to react plenty fast enough, which was one of my concerns. My other concern is the orifice getting clogged. I suppose only time will tell, but the oil filter should remove any particles that are big enough to clog it.

[lpaaruule]

I finally got a chance to see how the 0.01" orifice fitting worked in flight. I think that this may be the first time I've flown where I didn't get a pressure warning. The pressure was 46psi the entire flight, maybe varying one or two psi with RPM changes. I only got a pressure warning after I landed and the engine was idling at 900 RPM. The pressure was just below 31psi. I had taped up the oil cooler intake a little too much, and my oil temp was around 208F during flight. Made for some toasty cabin heat though.

The 0.01" orifice may be smaller than needed, but I'm leaving it alone unless it gets clogged.

[builderflyer]

Good going, Paul. I also purchased the stainless steel restrictor except I went with the one with an orifice diameter of 0.029". Why? Because that's what the diameter of the orifice was on the VDO type sender that I removed to replace with the Kavlico transducer. Before deciding on the 0.029" diameter, I attempted to determine what the rate of escape of oil would be for various orifice diameters but I eventually gave up. My engineering degrees are way too distant in the past. It'll take someone like Jeff or David A. or someone else to make this calculation. If any one cares to try, these are the parameters that I'd like to see addressed.......orifice diameter 0.029", 54 psi, 20w50 oil viscosity, and other assumptions needed to solve the problem such as entrance loss coefficient.

Art,,,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,Jabiru 3300 #261

[GordonTurner]

Just looking at the McMaster chart for water at 40psi...

.010 gives .016gpm which is 62 minutes to flow one gallon.

.029 gives you only 8 minutes.

I’m not sure at what point during the leak scenario you would likely be able to notice and conclude you had a leak, but if the .010 orifice works it sure gives you a better chance to get on the ground.

[builderflyer]

Just looking at the McMaster chart for water at 40psi...

.010 gives .016gpm which is 62 minutes to flow one gallon.

.029 gives you only 8 minutes.

I’m not sure at what point during the leak scenario you would likely be able to notice and conclude you had a leak, but if the .010 orifice works it sure gives you a better chance to get on the ground.

Gordon, as you probably know, the viscosity of aircraft oil is much higher than the viscosity of water. And the viscosity of the fluid dramatically affects it's ability to flow through an orifice of any given dimension. That's why I suggested that maybe someone smarter than myself could do the calculation to determine more closely the rate that oil, not water, would escape through the 0.029" orifice. VDO may have known what they were doing when they sized their sender orifice. Hope so.

Even so, if one lost all their engine oil in less than an hour, it better have been a very short flight.

Art,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,Jabiru 3300 #261

[GordonTurner]

Hi Art. Of course I didn't mean to imply the times given with water at 40 psi applied to hot motor oil at xx psi, but I would be surprised if the relative time difference, about 8x for about a 3x difference in diameter would change. I was trying to point out the advantage of the smaller orifice, assuming that it is shown to work effectively, in some kind of relative numbers.

Thinking about a 1/8” line with no orifice, egads. You’d be out of oil in less than a minute I guess.

[GraemeSmith]

My high pressure pulsing seems to be temperature related. Especially on cold days - even when the oil has got good and warm - it still sometimes pulses. So I thought I would start with the easy: Shield the pressure sender from a cold air blast.

Where top mounted on my AeroVee - the sender is sufficiently "far" from the engine case that perhaps it just doesn't stay warm enough.

So I wrapped a bit of AlClad around it as a quick and dirty trial baffle to keep the air off it - and it seems to have solved the problem this morning when the ground temp is -5C - typical for when it happens. Once the oil was warmed up - it stopped happening.

Going to refine the baffle a bit now.

(for some reason my correctly sized pics won't upload this morning - but basically - I just kept the cooling air blast off the sender.)

[gammaxy]

My high pressure pulsing seems to be temperature related. Especially on cold days - even when the oil has got good and warm - it still sometimes pulses. So I thought I would start with the easy: Shield the pressure sender from a cold air blast.

Are you using the VDO sender? If so, this sounds awfully similar to how they behave as the slider inside wears out. Higher resistance is measured as higher pressure. If the slider has a poor connection inside, it's possible for the measured pressure to pulsate between the actual pressure and some much higher pressure. It'll be interesting if shielding it continues to work for you.

Amusingly, I replaced mine with the Kavlico sender and was going to post about how much better it was until the exact model I used became subject to the Service Bulletin due to leaks. And the new model seems so huge that it really needs to be mounted remotely (in reality, they should all probably be mounted remotely).

[Friesen5]

I ordered and installed the Swift sender in my Sonex with a GRT EIS. It is mounted on the motor mount near the firewall and is fed with a braided hose from the front of the engine. Not intentional, but I have a restrictor fitting at each end of the braided hose. Oil pressure is read on Aux 2, with the settings suggested by GRT. The pressure readings are similar to the previous VDO sender. I notice a bit more variation than previous. Maybe it’s a bit more sensitive. My hope is that it won’t wear out as quickly as the VDO.

Mervin Friesen
Sonex 122