![]() |
Rivethead,
Nice writeup and setup. One tube is connected to an old oil fill cap. Where's the other tube connected to the engine? Thanks Tom H. |
Design consideration
I looked into building my own dessicator before finally purchasing a Tanis dehydrator. While expensive, it does have a built in heater for renewing the silica crystals.
The unit also has a digital thermo / hygrometer that records hi and lo readings. I use this in concert with the blue colored crystals to determine when to renew the silica. I've been using the unit for over two years now, and I'm glad that I purchased the unit, as I find myself using the heating unit far more often that just every couple of months. During dry periods, I've gone 2+ months, but there have been a couple of periods where I had to dry out the crystals after only 4 weeks. After seeing the unit first hand, I've often thought about how to go about duplicating the unit. It is essentially a toolbox with a gasketed / hinged lid, and a small plastic centrifugal blower over the top of a tub of silica inside of the box. Also buried in the tub with the silica is an insulated heating wire (similar to a water pipe heater to keep them freezing in the winter). It takes between 4 and 6 hours to dry out fully saturated crystals, but I normally put the system in the renew mode while I'm out flying, and rarely do I have to do a full heating cycle. The draw side of the blower fits to the oil dipstick tube (works great for pulling out water vapor just after flying), while the pressure side goes into the crankcase breather. When I know I'll be away for more than a few days, I stuff a red rag into both exhaust stacks -- be sure to leave some hanging out so you remove them before start. Don |
Doug, I got a 30-60 gallon pump and don't consider it enough even though it may be.
|
I finished mine last month for under $40 which included a new plastic Stanley 16" tool box from WalMart. Mine is a closed loop system drawing through the breather vent tube, into the tool box holding the silica bottle at one end and sucked out through the other end via the aquarium pump with a stone filter buried in the silica. The dry air then is pumped into the oil filler tube sealed with a rubber stopper. I like Rivetheads use of an old filler cap to screw on and will modify mine to do the same. My stopper worked loose one time. Its a nice portable system with everthing self contained in the tool box.
|
Todays flight to Pueblo was uneventful. Upon return home and after putting the plane in the hangar I removed the oil filler cap and some vapor came out. This was five minutes or so after engine shutdown.
I left the cap unscrewed to allow vapor to escape and came back about 30 minutes later. No obvious vapor. I put the dehydrator output into the crankcase breather hose bottom and plugged the system in as I was looking at the oil filler tube. After less than a minute I believe that I saw more vapor coming out. No flashlight so this observation has some uncertainty. If correct, it appears that my lowly 30-60 gallon Tetra whisper pump is doing some good. This is not a closed system at this point. |
In answer to a couple of questions. There was a choice between a 10, 20, 40, 60, or 100 air pump. I have no idea what the numbers actually stand for so I assume (I hate asking store help anything) they are suggested aquarium size. I chose the 60 as a guess and found that the air moves quite enough. I have access to an anesthetic machine and at some point may measure the actual air flow using the meter on that unit. A conservative guess from anecdotal evidence shows me that the unit moves about **.5 cfm. I consider this way more than enough since the entire internal volume of an assembled engine can't be more than a couple of cubic feet and is probably far less. Pumping air 24/7 .5 cfm becomes a lot of air exchange. Return air is sent back into the engine via the breather. Pictures of that area were so poor I didn't bother resizing them to post. I have a question of my own now for dtw_rv6. In the system you bought you say it dries your silica gel using a fan to move air over the crystals. Q: Where does the water vapor go after it leaves the gel? Is it somehow vented back to the general atmosphere? I'm assuming it's not being returned to the engine that's been dried out but I'd like to know how it's done with a, closed?, system. Also another point bothered me. I spend to much time dwelling on minutia and every new project I enter into begins with more research than it probably deserves, but. From what I've discovered, and I've mentioned this before, Silica gel takes several hours in a hot oven to thoroughly dry on the other hand Cobalt Chloride, the blue stuff, readily dries in a fairly short time at a significantly lower temp, 250* hot. All of the suggested temperatures I've found are hotter than most plastic tool boxes that I've ever seen can stand. With that said "Thoroughly" becomes a key word. There is a technique used in preserving art using Silica gel to hold air in an enclosed space at desired humidity level. The process used is a type of "tempering" of the gel to work only in a very small range. I'm wondering here (I'm not trying to disparage your unit) if your not actually training your dehumidifier to keep the air at a higher than optimal level for your engine.
(edit) I'm noticing people liking the use of my dip stick cap as a modified tube inlet. I used the old cap rather than using a rubber stopper or cork because occasionally it rains in my hanger and I really didn't want to find a puddle of water settling into my oil filler tube around a stopper. So far the old hanger only gets damp with a few local areas of leaking water from the roof in bad rain storms. I've never had any part of the engine actually get wet other than a little dew so in this case it's precaution. That old cap was available and turned out to be very easy to drill out. (another edit) ** Curiosity got the better of me so I measured the air flow. Turns out to be 7 liters per minute @ the return end of the system. |
I followed the Barker instructions for the 2 liter soda bottle type and it came out great. Also, it is a closed system and cost about $30.
|
Quote:
|
Danny, the stone filter/bubbler appears to be a way to keep desiccant dust out of the engine. Why do you suggest that it is not needed?
|
I have avoided the return system cus I didn't want to get oil vapour into the dessicant. Notsure if it will or not. So I use a once thru using ambient air. I did find that using a 5 foot tall column made the dessicat last longer....trouble is this added to the pressure drop so I had tochange to a bigger pump. Petco have those own brand now and for $12 I bought one that is a monster compared to my tetris thing. Pumps way more air.
Oh ifound cheapest place for dessicant was good old harbor freight at $5 for 2.2lbs and this is the indicating type |
| All times are GMT -6. The time now is 08:17 AM. |