Anyone build or buy engine dehumidifier?

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Here is a photo of the MIL-PRF-131 dessicant bag. It's multiple layers and very strong. I am convinced that Protective Packaging could fabricate a barrier bag that would encase the entire cowling of a Cessna 140. There website shows what appears to be a sealing tape on large items, such as jet engines. If you can make the barrier bag successful, it requires only dessicant ($5 for 2 pounds), a humidity plug, a shop vac, and a heat sealer. The bag and heat sealer are the most expensive items, but can be reused.

Again, my situation is unique with the engine stored outside the aircraft, but some ingenuity could be applied to do something similar for an engine inside of a Cessna 140 cowling. I could imagine a very large bag that when around the propeller and exhaust stacks with the only field seal back at the firewall where the cowing mates to the fuselage. I see that Protective Packaging does cell a jet engine inlet kit to seal the inside of an engine from the outside air. The pictures on their website seem to suggest a seal made with some kind of tape.

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Forgot the photo of the engine inside the bag before sealing

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Those look like a great set up for long term storage... I'm looking more for helping in between flights, but if I'm going to have to put her away for a while I am going to remember those!

I'm going to build one but without the drying bulb- I think that just overcomplicates the set up. I'm going to do a closed loop, but hook it open for a few minutes to blow the worst out the vent, then close the loop. I plan on putting an battery operated hygrometer in the system, when its not keeping up I'll swap out the silica for a fresh dried bucket of it...

BTW the cheapest silica is silica kitty litter at wally world. Its just plain straight silica w the blue indicators, but it truly is straight silica gel like they sell at Michael's or wherever ppl buy silica, its like $7 for 5lbs...

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If you decide to go that route, attached are some photos of the David Barker dehydrator kit that I built. You're correct in that the self-rejuvenating dessicant light bulb adds complexity, including a scuba valve that opens up when the bulb is on to allow the water vapor in the dessicant to escape. Barker's design is ingenious, but I could never figure out if it was working because I was not sampling the relative humidity of the air inside the engine.

The photos are of the kit on top of the crate I was using at the time to store my engine. All the plastic tubes ran to the spark plug holes and engine breather/filler cap through the crate. I purchase an inexpensive oil filler cap for experimental aircraft and cannibalized it to insert a barbed end fitting for the Tygon hose. I bought the hose and barb fittings from McMaster Carr.

One recommendation I would make is that you replace the aquarium pump with something more substantial like a vacuum pump to pull air through at a greater flow rate and circulate it through the dessicant more effecively. Another idea if you want to forgo the pumping and drying aspect is to purchase a small 2,000 psi nitrogen bottle like the ones used to pressurize beer kegs and a regulator and bleed dry nitrogen through your engine. You'll not be able to reclaim the gas of course, but there are no moving parts involved. Since nitrogen and air are about the same density, once you flood the inside of the engine with nitrogen, you should not need much flow to keep the blanket intact.

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Last photo of David Barker dehydrator kit assembled.

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One recommendation I would make is that you replace the aquarium pump with something more substantial like a vacuum pump to pull air through at a greater flow rate and circulate it through the dessicant more effecively. Another idea if you want to forgo the pumping and drying aspect is to purchase a small 2,000 psi nitrogen bottle like the ones used to pressurize beer kegs and a regulator and bleed dry nitrogen through your engine. You'll not be able to reclaim the gas of course, but there are no moving parts involved. Since nitrogen and air are about the same density, once you flood the inside of the engine with nitrogen, you should not need much flow to keep the blanket intact.

For discussion sake, I'm going to argue the idea of a faster pump... I would assume the advantage of the slow pump is the slow drawing of air through the desiccant, instead of fast... So the silica has more time to absorb the moisture...Seems like the low flow over time would be just as effective, if not maybe more that pulling through the desiccant quickly... Though that thought seems more geared towards an open system where you have to continually dry "new" air.... My concern with a fast pump, especially on the open system is it would suck ambient air through the Silica so fast that it wouldn't give it much chance to absorb the moisture. I may be more inclined to agree with the faster pump for purging the nasty air right after shut down.

Does any of that make sense?

Let me ask this about the Nitrogen... is that something one could "weep" into a closed loop drying system, I guess I'll have to study more on the nitrogen concept..

I guess I have time too as the pre-buy/annual keeps getting delayed... tomorrow now I'm hoping...

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The David Barker dryer kit is a closed loop system, which is what I built. So, it recycles the air in the engine crankcase by pulling from the breather port and then puts it back into the oil cap. So, all I was saying is that with all the flow losses of the tubes and dessicant bed, I recommended a stronger pump. I presume the aquarium pump was chosen by Barker because it was inexpensive and low energy consumption. Other than leakage thorough other parts of the engine that introduces moisture laden air into the circuit, once the air has been dried in the crankcase, it should stay dry. The higher flowrate pump should achieve the dry air end more rapidly, albeit, it could increase the leakage of moisture laden air into the engine through say the crankshaft seal by setting up a greater pressure differential. I have not thought about how to turn a vacuum pump into a closed loop pump, but even in the Barker kit, the aquarium pump needed to be modified to make it closed loop. There may be other pumps out there that are like aquarium pumps but provide a higher flowrate.

The use of N2 would be a substitute for the dessicant drier. Jet engines are stored long term in cans with a positive pressure N2 atmosphere. If I was to set up an N2 system for an aircraft store in a hangar say, I would pump N2 into the oil dipstick cap, and let it purge the crankcase air out the crankcase breather port. Then, I would plug the breather port by attaching it somehow to a relative humidity indicator plug or gage. This would allow you to monitor the RH inside the engine. If the RH increased slowly enough over time, you could the re-purge the engine by opening up the N2 regulator a bit to repurge th system.

With any setup, there are going to be leaks that prevent indefinite preservation without some kind of maintenance action. Generally speaking, positive pressure setups are easier to maintain a controlled atmosphere rather than vacuum systems because vacuum seals are harder to make.

In any system you choose, you'll have to run a experiment to see how much maintenance action is needed to keep RH < 40%.

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Makes complete sense! Just thinking what if you took small air compessor and built or bought an airtight container for it, and ran it metered out very slow but more oomph that a fish pump... you could make dessicant inline filters, even placing then outside the box, so air was going through them in and or out.... you could get a water seperator too to grab some of the water.... compessor wouldnt run much most likely....

Hmmm am i onto something or nuts?

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One like this

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Rough Sketch of my thought... I understand a closed system isn't truly "sealed" so perfect air tight may not be necessary but relatively so it wasn't just constantly new ambient air going to compressor. Probably would need to put the compressor in the box full so it wasn't forced to pull air through any leaks to compress it. I would also run the drain from the tank out the airtight box to drain that outside the box... sketch shows water separator in the box, but may be easier to mount that on the outside of the box but before the desiccant filter so anything it gets can be drained. So the air would get some "dehydrating" from the compression too, so would take some "heat" off the desiccant filters. I would also think a fibrous or paper filter would be smart too after the filter to make sure no silica dust was being pushed through... I'm kinda thinking this would be the bees knees...