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12-28-2008, 08:21 PM
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Join Date: Aug 2005
Location: Estacada, OR
Posts: 787
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The system dries for the crankcase, not the cylinders, keeping a positive pressure there and most of the air probably goes out thru the vent. Use dessicant plugs to protect the cylinders if you aren't going to fly for awhile.
Here's another approach for the crankcase, or one you can use in addition to the dryer. Every time you put the plane away after flight, open the oil filler cap, then put a wet/dry vacuum on the crankcase vent while the engine is still hot. The vacuum will suck out vapors before the crud condenses on the metal. The air you suck in thru the oil filler cap contains less moisture and none of the corrosive byproducts of combustion. Only takes a couple minutes. Does it work or is it a crackpot idea? A guy who ran his Bonanza engine for 2,600 hours, about 800 beyond TBO publicized the idea. You can smell the crud while you run the vacuum, so you know it's sucking stuff out. I think it works; it can't hurt.
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Richard Scott
RV-9A Fuselage
1941 Interstate Cadet
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12-28-2008, 08:44 PM
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Join Date: Jun 2005
Posts: 3,275
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Richard, a few weeks ago I opened the oil filler cap just after a flight and there was vapor of some sort coming out. Sounds like a plan if I can just remember it. Still need to finish that engine dehydrator.
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12-28-2008, 09:13 PM
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Join Date: Jan 2005
Location: SoCal
Posts: 2,061
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Sounds like a fine idea as long as the vapors you're sucking through the shop vac are non-combustible. Those motors are not without sparks.
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Steve Zicree
Fullerton, Ca. w/beautiful 2.5 year old son 
RV-4 99% built  and sold 
Rag and tube project well under way
paid =VAF= dues through June 2013
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12-28-2008, 09:34 PM
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Join Date: Oct 2006
Location: Glendale, AZ
Posts: 256
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venting the crankcase
I open my oil filler cap and let it vent every time I land for the day. A fair amount of visible water vapor escapes. I have no data on whether it really helps, but I feel better getting all that water vapor out of the crankcase. Never tried the vacuum, preferring to just let nature and heat do its thing. Interesting idea.
Quote:
Originally Posted by RScott
Every time you put the plane away after flight, open the oil filler cap, then put a wet/dry vacuum on the crankcase vent while the engine is still hot.
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Roger Whittier
RV7A Quick Build, Tip Up
N1MY Reserved - Canopy finished - Wings mated, Engine hung, electrical 95%
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12-28-2008, 10:19 PM
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Join Date: Jan 2006
Location: PA
Posts: 264
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Quote:
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Every time you put the plane away after flight, open the oil filler cap, then put a wet/dry vacuum on the crankcase vent while the engine is still hot. The vacuum will suck out vapors before the crud condenses on the metal. The air you suck in thru the oil filler cap contains less moisture and none of the corrosive byproducts of combustion. Only takes a couple minutes.
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Or modify an old hairdryer to disable the heating elements, put a reducing cone on the output end, and run it on a low setting for a few minutes through the oil fill/dipstick tube to blow the worst of the vapors out the 'case vent.....
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Ken
Helicopter mechanic (A&P)
USAFR KC-10 Boom Operator, on final approach to retirement
My RV-9/8/7 dream may be on life support, but it ain't dead yet!
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12-29-2008, 10:17 AM
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Join Date: Mar 2007
Location: Corvallis Oregon.
Posts: 680
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This is very timely for me. Since moving my project out to my hanger it has become a little more exposed to the relative weather. I have been looking for some sort of fan or air pump to use for a closed circuit air dryer. Good post, it gives me a little more hope of actually being able to come up with something.
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02-05-2009, 07:27 PM
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Join Date: Mar 2007
Location: Corvallis Oregon.
Posts: 680
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Time for my follow up. Engine dehydrator units have become a fairly large and recurring topic of discussion at the Eugene Oregon EAA chapter meetings during the last couple of months. Our Ex president and chapter founder “Wally Anderson”, known best in our circle as the creator and driving force of Synergy Air, had visited Northern Europe where the use of home made engine dehydrators apparently is common. At our last meeting Wally brought a unit he had constructed from parts easily found or purchased. His project was inspiration to me and I set off to construct a simple unit to use on my own engine while my engine basically sits on the nose of my unfinished 7A. With slight modification to the engines inbound air connection I'll be able to continue the use of the air desiccator unit (pictured below) after the completion of my 7A project. My cost of parts (less Silica gel) came to just a touch over $30.00 and assembly of the parts assortment took about one hour and fifteen minutes. Among the parts are, Storage containers from K Mart which were to my surprise of very good quality and very air tight, three short threaded tubes (the type used to construct lamps with), One fairly high volume aquarium air pump, One medium dab of red RTV used to seal the wire excursion through the main canister wall, Three feet of vinyl hook up tubing for the air pump and Twelve feet of larger diameter vinyl tubing for the unit to engine run, One short piece of porous tubing (also found at the pet supply store) for use as an air diffuser inside the desiccant canister. I ended up with a few varieties of Silica gel. I found some fairly course gel at the local industrial compressor shop which given the size of the bag I was able to purchase didn't fill my second stage canister quite enough to please me. I found a One and a half pound bag of Silica gel at Michael's craft store. Craft store gel is similar to course beach sand and at first the grain size was a bit of a concern to me as to what it's overall compaction and resistance to air flow would be, However, it turns out that it works just fine. Water bottle tests of the finished unit show the assembly to have a very adequate stream of air being returned to the engine. So with that here is how it works. Air enters the main canister through the top. The air pump sitting on the bottom of the main first stage canister and to one side vacates the air from the large first stage canister to the small nested second stage canister via small diameter vinyl tubing which penetrates the smaller canister through a slightly under size hole. Connected to the tubing from the air pump and secured to the bottom of the second stage canister is the optional porous bubbler tubing to encourage the diffusion of air. Both canister lids are connected permanently via one of the short threaded lamp tubes. As you can see from the pictures the small canister is where the desiccant lives.

Last edited by Rivethead : 02-06-2009 at 12:10 AM.
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02-05-2009, 09:57 PM
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Join Date: Jun 2005
Posts: 3,275
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I got mine going about two weeks ago. The clay-like desiccant had no moisture indicator so I bought the Michaels desiccant with color changing crystals. I want to find some desiccant that is coarser than Michaels.
I got a 30-60 gallon pump from Walmart but want more air flow. At least I am pumping some really dry air in the engine even if not optimal.
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02-06-2009, 12:47 AM
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Join Date: Mar 2007
Location: Corvallis Oregon.
Posts: 680
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I've noticed a common misstatement throughout this thread. Although in the long run it's not important it may be good information for others that collect this sort of useless info. Silica gel doesn't turn turn pink when it's saturated, it's the indicator pellets or grains that turn pink. Indictor pellets or grains are Cobalt Chloride and are readily dried in a 250* hot oven. Apparently Silica gel takes a hotter, longer oven to dry out thoroughly, in other words your indicator will have dried out long before your Silica gel has had much of a chance to dry. To make matters worse there is a coated Silica gel (coated with Cobalt Chloride) that does turn pink when saturated but that gel becomes "worn out" after several cycles of saturation because the Cobalt Chloride migrates into the individual grains of Silica gel and loses the obvious effect of color change. From what I've been able to gather once you have your batch of Silca gel or Cobalt Chloride you pretty much have all you'll ever need so long as the quantity you need doesn't change.
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02-06-2009, 07:46 PM
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Join Date: Jan 2006
Posts: 106
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Rivethead
Last week I pulled my left magneto to replace the carbon brush and cam to comply with SB2-08 and SB3-08. I was appauled at the rust on the parts from inside the accessory case of my 100 hrs TT Aerosport O-320 Lycoming. Needless to say I?m building a dehydrator this weekend. I like your style better then the 2 liter bottle method due to the fact your system is a closed system in regards to air circulation. Leaving the pump in open air would seem to simply suck ambient moisture from the surroundings and dumps it into the dessicant. Your system should be a lot longer between drying periods of the dessicant.
As I round up parts my main question is on the pump. What is considered ?high volume?? I went to the pet store and they are classified as per 10gallon, 20gallon, etc. What size in gallons is considered adequate? The 10 gallon was $20.00, the 20 gallon=$25.00. I went with the 20 gallon, but if it is not enough I can exchange it for larger.
Also, You have any extra old oil dipstick caps laying around that can be drilled out? I liked that idea also.
Thanks
doug
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