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04-26-2011, 10:24 AM
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Join Date: Jan 2005
Location: Powder Springs, Ga
Posts: 309
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Different Approach
Dan,
Go back and ask for what they have and given them the specs. you need. Opening and closing temps, length and dia. They will come back with several items that match your specs and maybe you can narrow it down from there. We have to do this at work to get around the agreements between OEM and vender.
__________________
Kurt Lohmueller A&P, DAR
Powder Springs, Ga
RV6A "Kurt's Toy" - Flying
RV12 - Flying - Sold
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04-26-2011, 04:00 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Ahhh, the joy of education and recreation....
Last night I started thinking about how it works. A few things had no apparent answer, and that sent me back to the hangar.
Today's lesson: do not remove the core from the holder before you boil it.
When removed from the holder you'll find a length of 1/4" dia rod inserted into a deep bore in the butt end of the core. What you don't know (and can't see) is that the end of the rod is against an internal piston. When the core is heated the internal piston pushes the rod, which pushes against the holder. That forces the entire core out of the holder against the pressure of the small diameter spring, which is stopped against the retainer clip in the slot.
Heating the core without the other parts just moves the internal piston. You won't see any length change on the outside. Unlike some illustrations out there, the rod in the nose of the core (with the nut) never moves. It is a stationary post upon which the seat cone can slide in the event oil pressure (because of a blocked cooler) overcomes the pressure of the large diameter spring.
When heated as an assembly, look for the length increase between the holder and the seat for the big pressure relief spring:
When it cools, the small diameter spring forces the core to retract into the holder.
The measurements in the drawing are for my vernatherm....yours may be slightly different.
Careful measurement says the depth of the bore in the oil filter adapter into which the assembly is screwed meets the factory spec, 3.277" deep from the seal surface to the seat edge of the bypass passage. A plot of length change vs temperature says the cone should touch the seat (and block the bypass) at about 188F. That's about right; the holder is marked "85C", which would be 185F.
No crime in ignorance if you don't stay ignorant, right?
BTW, looks like the valve is in the Rostra 3255 series:
http://rostravernatherm.thomasnet.co...lves/pn-1011?#
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Last edited by DanH : 12-23-2014 at 06:29 AM.
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04-26-2011, 04:07 PM
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Join Date: Nov 2005
Location: Davis, CA
Posts: 1,156
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Reading between the lines, yours is functional?
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Lars Pedersen
Davis, CA
RV-7 Flying as of June 24, 2012
960+ hours as of June 30, 2020. Where did the time go?
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04-26-2011, 04:15 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Well, I think so, but at this point I have my antenna up....wondering if I've missed something else. God is in the details.
For example, consider the pressure relief spring. As mentioned in the previous post, careful measurements says the cone should contact the seat at about 188F....but that doesn't mean it will seal. There is a pressure difference between the two sides of the bypass hole. The cooler pressure drop per the SW chart is 3.5 psi at 235F OT and 46 lbs/min. Add hoses, fittings, and a more realistic oil temp (more viscosity) and the total difference is probably 10 psi or more. The bypass seems to have an area about 0.25 sq in, so the vernatherm will actually need to extend far enough to compress the pressure relief spring to 2.5 lbs. Put another way, it won't actually seal at 188F. Full sealing will require some higher temperature.
I have the vernatherm in my hand right now, and I can compress the spring about 0.125" with just my thumb and forefinger. Don't know the actual spring rate, but I'll find out tonight. It's not real stiff:
Here's the thing. Recall that temperature vs length plot? Unloaded there's only 0.040" between 190F and 212F.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Last edited by DanH : 12-23-2014 at 06:31 AM.
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04-26-2011, 06:52 PM
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Join Date: Dec 2008
Location: Big Sandy, WY
Posts: 2,567
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Maybe you just have really strong fingers, eh. Seriously though, am I thinkng right that you could shim from the back to increase seat pressure as a test experiment? I know you know how little leakage it takes to affect oil temp. You're pretty confident with the seat fit?
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Actual repeat offender.
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04-26-2011, 07:22 PM
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Join Date: Jul 2007
Location: Keller, TX
Posts: 1,553
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Quote:
Originally Posted by DanH
No crime in ignorance if you don't stay ignorant, right?
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If ignorance WAS a crime, I know a lot of people who would be serving consecutive life sentences!!!
Lots of good information in this thread. I checked my Vernatherm a few years ago and the length change was right, but I remember the spring being much stiffer. I was not able to pull it back like Dan did. Would that imply that once it reaches the seat it would seat tighter faster with less increase in temp?
__________________
RV-8 180 hp IO-360 N247TD with 10" SkyView!
VAF Donations Made 8/2019 and 12/2019
"Cum omni alio deficiente, ludere mortuis."
(When all else fails, play dead.)
Last edited by Bubblehead : 04-26-2011 at 07:25 PM.
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04-26-2011, 07:29 PM
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Join Date: Mar 2007
Location: Sonoma County
Posts: 3,821
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Quote:
Originally Posted by Bubblehead
If ignorance WAS a crime, I know a lot of people who would be serving consecutive life sentences!!!
Lots of good information in this thread. I checked my Vernatherm a few years ago and the length change was right, but I remember the spring being much stiffer. I was not able to pull it back like Dan did. Would that imply that once it reaches the seat it would seat tighter faster with less increase in temp?
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No, it would just have a higher bypass relief pressure.
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04-26-2011, 08:05 PM
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Join Date: Feb 2005
Location: Huskerland, USA
Posts: 5,862
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Quote:
Originally Posted by Ironflight
Interesting comment, and nothing against a thermostat...but USELESS?!
I've had them in airplanes for decades - have never had one fail on me. I know that others have, of course - but since everything gets archived around here, that's a pretty extreme statement without a lot more data...
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"Useless" may have been a poor choice of words on my part. I was needing to get somewhere and posted what I was thinking.
I cannot figure out why more builder don't install oil thermostats. We have used them on Rotax 912's for a decade. Dan, you need to take a hard look at an oil thermostat. Toss that goofy vernathing, and design a modern cooling system.
http://thermostasis.com/
__________________
RV-7 : In the hangar
RV-10 : In the hangar
RV-12 : Built and sold
RV-44 : 4 place helicopter on order.
Last edited by Geico266 : 04-26-2011 at 08:22 PM.
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04-26-2011, 09:25 PM
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Join Date: Jan 2008
Location: Euless, TX
Posts: 64
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I'll show my ignorance and sign up for my life sentence but isn't a Vernatherm just a particular brand and configuration of an oil thermostat?
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Sully
RV7 N627RS
Moving into Phase 1
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04-26-2011, 09:45 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by aerhed
Maybe you just have really strong fingers, eh.
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Apparently yes
I just came from the shop and measuring the spring rate. This pressure relief spring starts compressing at 14.75 lbs. That matches Lycoming statements about the relief pressure being 60-90 psi drop across the cooler circuit; a pressure relief valve with a port area of 0.248 sq in and a 14.75 lb spring would start to open at 59 psi. The spring rate is quite flat; it only rises to 17.75 lbs at 0.110 compression.
Anyway, the spring is not soft enough require any significant vernatherm extension past initial contact in order to overcome ordinary cooler circuit pressure drop.
Quote:
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I know you know how little leakage it takes to affect oil temp. You're pretty confident with the seat fit?
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I'll take look up the bore. The cone has a nice even contact line all the way around.
Quote:
Originally Posted by Geico266
I cannot figure out why more builder don't install oil thermostats. We have used them on Rotax 912's for a decade. http://thermostasis.com/
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The referenced Rotax oil thermostat is a different vernatherm configuration in a different package. It does not include a pressure relief valve.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Last edited by DanH : 04-27-2011 at 05:46 AM.
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