Petco aquarium pump Pirep..:)

As some of you know I made a engine dehumidifier from two columns of coloured silica gel deissicant (Harbor Freight), a length of ABS pipe and a Petco aquarium pump..9902 I think is the model number... Its for a 60 gallon aquarium.

I have been running this pump for about 3 years and have been very happy with it. It has far more air output than the little tetris pumps.

Well the last couple of months I noticed the dessicant was lasting much longer before changing colour, I pulled the tube off the breather yesterday and found the flow had gone to almost zero.

That pump was a whole 15 bucks so feeling totally cheated I took the pump apart and found there are actually two pumps in one.. The diaprham had ruptured on the side I was using.

So I simply swapped to the other side and plugged it back in. Now of course the diapharam on the other side has been used for just as long so I don't know how long it will last.

It occured however that one could effectively double the life of the pump by removing the unused diaphram when first purschased and keeping it as a spare.

I mean why not.. Not as cheap as making your own earpices for the in ear headsets from foam earplugs but close..

Frank

What is an engine de-humidifier for? Do you hook it up to your engine after flying to get get moist air out?

Hook to the crankcase breather or where?

Curious

walkman said:

What is an engine de-humidifier for? Do you hook it up to your engine after flying to get get moist air out?

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You got it.

walkman said:

Hook to the crankcase breather or where?

Curious

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Exactly right. I just built one of my own using one of the tetris pumps. Works pretty good. I also incorporated a 100w light bulb to dry out the dessicant on occasion. There are a variety of complex ways to wire this together, but I went simple and am happy so far.

Some links with instructions.

here
and here

Thanks for the PIREP on the other pump! I'll switch when the tetris pump dies.

Cus I'm an HVAC geek, here is psychrometric explanation.

When you burn fuel you make mostly CO2 and water vapour. During flight some of that mixture gets pushed past the rings into the crank case.

Air at high temperature can hold a LOT more moisture than cold air.

So you land and you have a nice hot engine at sy 180F. The air inside the crankase is completely saturated (I know this because when i hookup the dehumidifier and crack open the dipstick tube I column of STEAM rising from the tube).

This saturated air at 180F now begins to cool, hits the dewpoint at say 150F and now condenses the rest of the moisture inside the crankcase.. The condensation probably drips all over the camshaft... My Psych chart doesn't go up to 180F so I can't give you actual numbers of how much moisture would be inside the crankcase..but its a lot.

So the dehum unit does two things..It expels this steam out of the case (at least it does before it cools and condenses into liquid) and then it continues to flush the case with very dry air..This air is so dry it picks up moisture from wherever it can..I.e it will evaporate left over moisture after the engine is cooled.

if you run a small block heater this will increase the partial pressure of the moisture.i.e it will evaporate more easily.

This is why frequent flying is recommended to keep a film of oil splashed on the cam..The cam is above the oil level in the case. A dehum unit is a more direct way to achieve the same thing for really low cost.

There endeth the lesson..

Frank

I am interested in building one of these. How have folks connected the crankcase air input fitting on a Lycoming engine? I can imagine removing the dipstick and connecting the air input fitting to the dipstick hole. Is there an easier way?

Nancy Jean

Yeah I just stuffed the tube into the crankcase breather tube and open the dipstick..allways nice to see the column of steam being blown out of the dipstick hole.

I am considering turning my open loop system into a closed loop.

The open loop system simply takes air from inside the hangar, pumps it through the two columns of dessicant (a 10' length of 1.5" abs pipe with two end caps with hose barb fittings screwed in the ends), into the breather pipe and out the dipstick tube.

For a closed loop I would take a cork drill a hole and attach a 1/4 tube. the pump would go in a sealed box and the return tube connected from the dispstick tube to the box.

This would probably make the dessicant last longer.

To recharge the dessicant I simply put it in the oven at 300F for a few hours..till it turns blue again.

The petco pump makes quite a lot of flow so there is no excuse not to feel the breeze blowing out the end before hooking it up each time.

I can take some pictures of my setup in a few days when I get back out to the hangar. It isn't quite finished though. What I have essentially done is exactly as Frank suggests for a closed-loop system. I don't have remotely as much dessicant so I want it to last a while between recharges.

I integrated the dip-stick air intake with a heating element. Specifically, this unit:

http://www.aircraftspruce.com/catalog/eppages/staywarm.php

I have a circular plug that fits in the filler tube and passes the heating element and output from the air pump. The air pump itself sits inside a very large glass jar filled with dessicant beads. The lid of the glass jar passes an electrical line for the pump and two air lines (input and output). The input connects to the engine breather tube via cork and a little tape. Mostly this was put together relatively quickly with just stuff I had laying around as a proof of concept. I'd like to fabricate a few pieces to make it a little easier to use.

Typically, I only hook this system up when the airplane is going to sit for more than 2 or 3 days.

The only point I would make is that if you don't use the dehumidifier unless the engine will sit for more than a couple of days is that you lose the benefit of extracting the steam while the engine is warm..I.e the nicely saturated hot crankcase air.

I.e as soon as the engine cools you will have liquid moisture in the crankcase which is harder for the dehumidifier to remove as it will have to evaporate first.

It might be just as effective eventually but seems to me you have the pschrometry working for you when the engine is hot so might as well take advantage of it.

FWIW.

Cooling condensation

I have know people that when landing, they open their dipstick fuller tube to let the hot moist air out. They do this at every landing where the plane will sit for a while such as, $100 hamburger stops and always at home base. Seen this for decades. Do you think this works to a degree. I have never seen any data on this method.

NickAir said:

I have know people that when landing, they open their dipstick fuller tube to let the hot moist air out. They do this at every landing where the plane will sit for a while such as, $100 hamburger stops and always at home base. Seen this for decades. Do you think this works to a degree. I have never seen any data on this method.

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I do not do that at an intermediate stop but I do when I return home. After a few hours I screw the dipstick in and install the engine dryer. I have no data but it just makes stoicheometric hydrological sense.

Yes opening the dipstick will ceratinly work to a degree..I mean if you can see vapour coming out then its coming out..which is always better than staying in...

Like you say though this is hard to quantify..If I find a psychromtric chart that goes up to 180F then I can have a stab at how much moisture ends up in the crankcase when it cools.

Frank