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RV-12: Manifold Pressure Hose Line

Geico266

Well Known Member
It was raining today so I pulled the top cowl to check things over. I decided to tidy up some loose wires, cables, and hoses, and look for chaffing. I noticed the black manifold pressure 1/4" ID hose that runs from the carb equalizing tube to the Dynon MP "signal converter" (mounted on the firewall) was extremely loose on the hose barb fitting. It looks like it has swelled up to a size much larger than .250 ID. The OD is .500 at the end near the carbs and the Dynon end is .435. The hose seems mushy also. I realize the Rotax is metric and the Dynon is English so finding a tube that fits both is tough, but this tube looks like it is swelling up from fuel vapors.

Any air leak will cause the engine to run lean and little rough. I don't recall the plans saying we should put any kind of clamp on it, but a little "double loop safety wire clamp" would certainly help prevent an air leak.
 
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I got a call from Marlon from MN, flying RV-12 for over 100 hours. His manifold pressure hose is swelling also. His was so loose it had almost come off. Time for everyone to check this, and add a safety wire clamp.
 
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I'll check mine in the AM

I changed the oil last weekend at 100 hours. I didn't see any problem with the manifold pressure line then; but I'll pull the top cowl and look again in the AM...thanks for the heads up Larry.

Jay Sluiter
Albany, OR (S12)
N124CS
110 hours
 
I hate to ask

an obvious question, but my aging memory says that hose may have been supplied by Van's, not Rotax, since the MP sensor wasn't Rotax. In that case it probably came out of their usual parts supply and may not be compatible with ethanol? I assume those with failing hoses are burning Mogas?

Wayne 120241
 
an obvious question, but my aging memory says that hose may have been supplied by Van's, not Rotax, since the MP sensor wasn't Rotax. In that case it probably came out of their usual parts supply and may not be compatible with ethanol? I assume those with failing hoses are burning Mogas?

Wayne 120241

Yes, I burn mogas, but I test for ethanol and I have never found any in the 92 octane I buy.
 
What is manifold pressure data used for by the rv12 operator/pilot?

You ask a good question....I just completed a Rotax Service Training class this past weekend where I asked the same question. Was basically told we use rpm as opposed to manifold pressure as our aircraft use fixed pitch props. Sorry...off topic. I likewise will check as to tightness of hose..

Maybe Scott will enlighten us on this one��
 
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an obvious question, but my aging memory says that hose may have been supplied by Van's, not Rotax, since the MP sensor wasn't Rotax. In that case it probably came out of their usual parts supply and may not be compatible with ethanol? I assume those with failing hoses are burning Mogas?

Wayne 120241

I think Wayne is spot on .... the same Van's supplied rubber hose is used for the coolant bottle and the manifold pressure. It is not a reinforced fuel line type of hose and looks like a standard rubber vacuum line to me.

I replaced that hose between the coolant expansion bottle and coolant tank with metric fuel hose because it split at the coolant bottle after a few months from being stretched to almost twice its normal size to get over the nipple on the tank .... guess I should consider replacing the manifold pressure hose with the leftover metric fuel hose and use Gieco's suggestion about using safety wire as a clamp. Actually have a tool that I picked up Oshkosh that makes nice hose clamps out of safety wire.

Happy building/flying
 
I replaced the MP this year at annual due to some minor chafing. When I reviewed the KAI it appeared this 15 inch long hose was supplied by Vans. I took it to my local ORiley auto parts and asked for a replacement on this original hose. The clerk disappeared to the back and returned with a duplicate in size, length, and rubber type. $.75 latter I was on my way and shocked at the low price.

I use a small worm clamp on the end that attaches to the crossover tube and just push the other end on the plastic receiver on the Dynon component. FYI the hose from the coolant fill location to the overflow also have a small worm clamp snugged down on both ends. This was something Jetguy suggested when reviewing his engine compartment during transition training and has served me well since 2013 and 170 hours
 
As a data point, my 2.5-year-old / 450-hour RV-12 has the originally supplied hoses and tubing and shows no signs of such distress. I have been using Mogas 91 with 10% ethanol (UGHH!) about 95% of the time. I believe it is still a good idea to keep an eye on such things since who knows what ethanol will do to various parts over time. Adding a line clamp or two probably wouldn't hurt.
 
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$.75 latter I was on my way and shocked at the low price.
You obviously didn't tell them it was for an airplane. :) Seriously though, yeah, I bought some hose from O'Reilly Aircraft Supply too when I did the 5-year hose replacement on my -12. It's pretty inexpensive even for good quality hose.
Actually have a tool that I picked up Oshkosh that makes nice hose clamps out of safety wire.
I bought one of those too, at my wife's suggestion. It's been a solution in desperate search of a problem ever since. Oh, I think I did use it once to secure a plastic water fountain hose on the pump outlet. It is a pretty cool little tool though, I'm sure some day I'll be really glad I have it.
 
Other than no MP indication, is there any other down side to capping off the fittings and reducing a potential hose leak source?

A lot of people with fixed pitch propellers use MP as the primary value when making power adjustment. On my fixed pitch RV-6A I rarely look at the RPM indication.
There are a number of discussions in the forums on the subject.

Here is one post I made previously on the subject.

http://www.vansairforce.com/community/showpost.php?p=985154&postcount=9
 
While acknowledging Scott's statement I would say that the RV-12 is the only fixed pitch prop aircraft I have flown that has MP indication. It's nice, but my primary power indication is RPM. I would not be concerned if it was not there.
 
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