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Feb 23, 2018, 11:36 PM
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Thread OP
Build Log

DIY Vacuum Pump Rig


Hey everyone, I've decided to try my hand at some nice shiny composite planes. Been kicking it around for a while and picking up pieces here and there. I initially tried a couple weeks ago to just use a bleeder valve to set the vacuum level but the oil vapor from the pump after a few hours filled the garage and the pump was around 140 degrees Fahrenheit so I bought a vacuum switch.

It's a zeny pump off Amazon, an airtrol vacuum switch, some PVC pipe for a reservoir and a vacuum gauge. Total cost was around $150, which is well under half the cost of a ready to go pump kit from most places. I'm bagging cheap white foam for now so it's set to 8 inches Mercury max, but it's nice and adjustable.

The documentation for the airtrol switch says it's rated up to 10 amps max by default, when I opened the pump wiring cover I was surprised to find a self resetting circuit breaker, rated at 4.5 amps. The switch should have no issues and not need a relay. I built a long pivot cutter hot wire bow and am hoping to get a wing bagged for a test this weekend.

YouTube overview

UPDATE: If you build a rig using a pump like this, at the minimum you need a check valve between the reservoir and the pump. After 8 hours of cycling overnight most of the oil migrated from my pump into my reservoir/layup...
Last edited by Space Goast; Feb 26, 2018 at 11:18 AM.
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Feb 23, 2018, 11:47 PM
Scott
Pylonracr's Avatar
I prefer very light white foam for my wings as well. As such, I set my vacuum switch to 5 Hg. I found that much more than that will crush the foam. Nice set up. My vacuum storage tank is some 4" ABS pipe, a vacuum switch from Joe Woodworker (very similar to yours) and 2 resin traps on ball valves so I can run 2 bags at once. Same idea as yours but a tad larger. You should be able to do just about anything RC related with that.

Scott
Feb 24, 2018, 11:34 AM
The Junk Man
If that is an oil-filled pump I would caution you about running it indoors. Oil pumps emit a fine mist of oil out the exhaust. It is very fine and almost unnoticeable until you start finding a thin film of oil over everything in your workshop. Not to mention breathing the stuff.

Most oil-filled vacuum pumps are for refrigerant checks and repair and are not meant to run in a confined space for very long.

Tom
Feb 24, 2018, 04:25 PM
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Tom, you've exposed my secret car preservation scheme! Forgive the mess, I actually spent all day cleaning the shop because I didn't have any clean workspace.

In all seriousness, I learned that lesson the hard way a couple weeks ago. I'm going to install a large exhaust fan that goes through the wall, I built the garage this past summer and already noticed it has poor ventilation while working. I'm also considering running a tube from the pump exhaust to the window, but since I put the vacuum switch in the duty cycle may be so short it's not needed.

Do you typically use a diaphragm style pump?
Feb 24, 2018, 05:44 PM
The Junk Man
I have half a dozen pumps. My son and I used them as hold down clamps when we were doing serious woodworking. I have built both of the Joe Woodworker vacuum systems, and still use one from time to time.

But for my toy airplanes my primary pump is a GAST diaphragm pump.

Tom

PS: Even with short-cycling an oil filled pump will emit oil mist. An exhaust hose routed outside will save you a lot of grief in the long run.
Feb 24, 2018, 09:49 PM
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I received a question via PM on the vacuum pump wiring, so I made a quick diagram.
Feb 25, 2018, 11:39 PM
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Well I started my first bagged wing, don't have high hopes for it, as I flipped it top to bottom with the glass wetted out the bottom layers shifted and I had to try to straighten them out, by the time I got that done and flipped again the epoxy had started thickening. The stuff I have from previous little projects is 20-25min pot life, I should buy some slower...

If it turns out, the plan is to make a powered plank. All I've flown so far is foamie and quads so no huge speed goals for this, probably 70mph(dives) and lower. I cut four cores to get two decent ones, a buddy cncd some templates I sent over out of aluminum. Even those two cores had some dips from the hot wire, filled them with spackle and sanded.

It's a one piece wing, 48" pw51 with 9" root chord tapering down to around 5". For layup I did two layers of 1.4oz cloth top and bottom and ripstop nylon for a live hinge. I didn't paint the mylars so I can see anything I mess up to learn... I did wax them though. I also dropped the vacuum down to just over 5" after Scott's suggestion and reading around on the forums.

Hopefully it turns out better than I think it will, but only time will tell...
Last edited by Space Goast; Feb 25, 2018 at 11:44 PM.
Feb 26, 2018, 09:26 AM
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Another day, another data point... Checked on it this morning before heading to work and the pump oil level had dropped a fair amount, and I could hear a gurgling sound after the pump cycled off, and it was cycling about once per minute. Turned the pump off so I didn't run it out of oil while I'm at work, clamped the line shut.

I'd seen check valves mentioned, but forgot to get one. I'll pick one up before I try again. The epoxy I used has 8-10 hour cure, so hopefully the wing turns out still.
Feb 26, 2018, 09:52 AM
The Junk Man
Yep. Those pumps are not meant to be used on anything near the duty cycle necessary for vacuum bagging. And all that oil didn't just "disappear", it went out the exhaust port into the atmosphere. You will also find the motor gets VERY hot if it short-cycles on and off... eventually burning out.

But, as my grandpa used to say, people that need experience get it, one way or the other.

Tom
Feb 26, 2018, 11:15 AM
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I actually taped a cloth over the exhaust to try to abosorb any oil that came out and it's dry. So now I'm more worried that all that oil got sucked into my reservoir and potentially the wing... I'm still trying to bandaid the system for budget reasons but I can definitely see the appeal of an oilless $400 diaphragm pump right about now...
Feb 26, 2018, 12:34 PM
The Junk Man
Quote:
Originally Posted by Space Goast
I actually taped a cloth over the exhaust to try to abosorb any oil that came out and it's dry. So now I'm more worried that all that oil got sucked into my reservoir and potentially the wing... I'm still trying to bandaid the system for budget reasons but I can definitely see the appeal of an oilless $400 diaphragm pump right about now...
GAST 704 units like mine come up on ebay all the time. WAY less than 400 bucks. And the thing about getting a quality pump is that parts are readily available and rebuilding one is a snap.

Tom
Feb 26, 2018, 07:00 PM
Entropy is happening!
Jim.Thompson's Avatar
Fridge pumps can be picked up for free. Old automotive vacuum advance mechanisms are commonly thrown out. I have read that a large syringe will also do the same job for a regulator.
My home made system, based on a recycled fridge pump cost me the price of the vac guage and the capacitor across the switch.
Both the regulated pressure and the dead band are fully adjustable.
It's been in service for all my composite building career. About 8 years or more.
Description can be found on my blog (I think?).

Jim.

edit: I vent the exhaust outside the shed. I have only added oil once or twice.
Feb 26, 2018, 09:00 PM
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The wing actually turned out better than I expected. A couple small dry spots where the epoxy started setting before I got it all on, and leading/trailing edge definitely need sanding. Definitely not winning any awards for its looks. The leading edge fiberglass tape was spray glued on and it turned a nasty brown color.

I stopped by an auto parts house and picked up a cheap check valve, stupid thing works about 10% of the time... Just blowing/sucking through it like a straw it occasionally will block airflow one way, other times it just let's air past. Put it on the pump and same result... I might keep an eye out for better pumps but since I already bought this one it makes the decision harder.
Feb 27, 2018, 08:42 AM
I build what I fly.
ibnjmn's Avatar
Quote:
Originally Posted by Space Goast
The wing actually turned out better than I expected. A couple small dry spots where the epoxy started setting before I got it all on, and leading/trailing edge definitely need sanding. Definitely not winning any awards for its looks. The leading edge fiberglass tape was spray glued on and it turned a nasty brown color.

I stopped by an auto parts house and picked up a cheap check valve, stupid thing works about 10% of the time... Just blowing/sucking through it like a straw it occasionally will block airflow one way, other times it just let's air past. Put it on the pump and same result... I might keep an eye out for better pumps but since I already bought this one it makes the decision harder.
Nice wing! I'm pretty sure that will fly.

It looks like you're using some small tubing, same as I'm using, and I found a fish pump check valve for a couple of bucks that works quite well. Maybe yours needs a higher flow rate to go off?
Feb 27, 2018, 09:18 AM
Safe landings!
Thread OP
Quote:
Originally Posted by ibnjmn
Nice wing! I'm pretty sure that will fly.

It looks like you're using some small tubing, same as I'm using, and I found a fish pump check valve for a couple of bucks that works quite well. Maybe yours needs a higher flow rate to go off?
Thanks! I've seen aquarium components mentioned, but have never messed around with aquariums but was familiar with automotive vacuum check valves. I might take a trip to the pet store and test some valves out.


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