Today's Message Index:
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1. 05:41 AM - Re: Variable Oil Pressure Reading (rampil)
2. 06:05 AM - Re: Variable Oil Pressure Reading (Roger Lee)
3. 10:20 AM - Re: Variable Oil Pressure Reading (JohnF)
4. 01:56 PM - Re: Variable Oil Pressure Reading (Roger Lee)
Message 1
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| Subject: | Re: Variable Oil Pressure Reading |
Hi Barry!
Cavitation requires massive pressure changes usually caused by flow in
hydrodynamic systems, high speed flow and shear. There is essentially no
flow in a dead end tube to a pressure diaphragm. If there is a bubble,
maybe you will get a bit of to-and-fro, but not the kind of shear to create
cavitation. Same reason bends really don't affect pressure transducer lines.
Small pressure changes like 0 to 60 psi would have to occur with huge
acceleration to cavitate oil, a fluid designed to have high surface tension.
Adding a length of tubing increases inertance and a wee bit of resistance.
Burping these engines is all about refilling the reservoir and preventing
entrained bubbles from blocking oil channels in the block which would
depress lubrication and heat transfer. Nothing to do with resonance
phenomena.
--
If you can't measure something accurately, you can't understand it:
paraphrased from Lord Kelvin
For the curious, check out the electrical analog, a pi filter here at
https://en.wikipedia.org/wiki/Capacitor-input_filter
--------
Ira N224XS
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=470322#470322
Message 2
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| Subject: | Re: Variable Oil Pressure Reading |
Hi John,
You didn't say if you did a full oil purge? If you didn't you still need to do
one before a flight. Yes air in the system can cause pressure swings and sometimes
after a purge, but should go away.
--------
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=470323#470323
Message 3
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| Subject: | Re: Variable Oil Pressure Reading |
Thanks for your suggestions/ideas. As I suspected last evening at home while thinking
over the problem it struck me that when doing the air purge after replacing
fuel and oil hoses that upon reflection that evening that I had "pumped"
a lot of oil out of the engine while doing the purging. I had originally put in
3-liters of new Aeroshell Sport Plus 4, but I suspected I had emptied too much
while purging.
This morning I refilled the oil to the top of the flats on the oil dip stick, purged
the oil system again, buttoned up the plane, and ran it up.
One thing I wanted to do is monitor the operation of the Thermostasis unit. It
worked perfectly, and got me up to 50-degrees C in a few minutes, high enough
to apply takeoff power if need be.
The oil pressure was rock solid, moving from 66psi/81-degrees F, to 55psi-122-degrees
F in those 3 or 4 minutes.
Problem was low oil quantity...now fixed. Reminds me what a mechanic once told
me: If you have a problem, look at the last thing you did.
Seems good advise still.
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=470333#470333
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| Subject: | Re: Variable Oil Pressure Reading |
Hi John,
Glad it worked out. I usually put in 3.5 liters for a good oil purge. One thing
about the oil purge is you don't need a lot of oil to come out. A small quantity
is fine. You're just trying to make sure the lifters have oil and there are
no huge air voids in the engine. It doesn't take that much excess oil to do
that. If you run low on oil during a purge you can pump air into the system and
cause those air voids.
--------
Roger Lee
Tucson, Az.
Rotax Instructor & Rotax IRC
Light Sport Repairman
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=470346#470346
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