Electrical Experts

[Poptart]

If anyone knows how to convert an air pump into a vacuum pump, please enlighten me. The basic design of the two units is shown below; I have the top one and want to make it into the bottom one. The company won't help. As it is, the unit pumps air through the outlet but has almost no draw through the inlet. There is a pair of duckbill valves in each head; the inlet v's down and the outlet v's up. I have tried reversing power lead polarity (no effect) and switching inlet and outlet fixtures (tubing) but not valves. I know there is a simple solution here.

 

[lightwriter]

I am assuming that it is a piston type compressor.
The pump function is deignated by it's mechanical configuration. Changing polarity and reversing the rotation of the pump will still result in the same function b/c the duck bill valves open and close by differentials in pressure. When the piston goes down, the pressure drop in the cylinder opens the inlet valve and closes the outlet valve. When the piston goes up, the pressure buid up in the cylinder opens the outlet valve and closes the inlet valve.

The air moved, air leaving the outlet, equals the mass of the air entering the inlet. If you want to get more of a differential pressure at the inlet (vacuum), you need to reduce the opnening of the inlet. This will increase the pressure drop, but also reduce the total mass flow as there will now be a restriction. All this is assuming that it is NOT drawing air from somewhere else. This could be happening as it is easier for the piston rings to seal under pressure than under vacuum. Put a plastic bag with a big piece of foam in it and tape it tight. See what happens. It should compress the foam but it will take it a little while to get all the air out.

Give me more info. I can help. Model and actual pics would help as well as what you will be using for. If you are modifying it for a fiberglass application it has to function really well. What kind of vacuum numbers are you trying to acheive.

 

[Poptart]

So if I change the inlets to small diameter nipples the vacuum will be there? I tried the smaller ones on the intakes but nothing seemed to change. I need enough vacuum to power my printing frame, which has 600 1/16" holes in its surface.
http://www.apollopumps.com/ is the mgf's website.

 

[lightwriter]

They are diaphragm type pumps according to the website. The principal is still the same. They are actually better at pulling a vacuum than a piston type because the diaphragm is the seal. These types of pumps do not have the ability to move large amounts of air very quickly. They still pull a vacuum; you just have to give them time to "suck" all the air out. Per their specs your pump, in the vacuum configuration, would take nearly a minute to move the air in a one gallon container at 0 vacuum (i.e. no restrictions) It has the ability to pull 2.3 psi of vacuum at 0 flow. This does not seem like very much to me. I would find out what the requirements of the printing frame are.

Changing the inlet to small diameter nipples will give you more vacuum at the nipple because the air would have to speed up in order to maintain mass flow. Now that I see what you are doing I would leave that part alone. You should let the end process be the restriction.

 

[Nick R.]

Poptart,
If you're close to the NYC area, I can lend you a vacuum pump. Otherwise, it'd be pricey to ship.
-Nick

 

[Bill K.]

Poptart,

Have you tried a small Shopvac. They have good suction and are not expensive.

Regards,

Bill K.

 

[Poptart]

I actually did start with a vacuum fan. I understand though that they're better at moving air than at creating a vacuum, and my initial tests indicate that the suction created is weak. Also, the motor is really noisy. I also have a "Re-Air" refillable compressed air can pump that's quiet but I can't even find a vacuum inlet. It's a piston type design. It has a great blower/fan that I could cannibalize but then the thing is useless as a compressor.

Per their specs your pump, in the vacuum configuration, would take nearly a minute to move the air in a one gallon container at 0 vacuum (i.e. no restrictions) It has the ability to pull 2.3 psi of vacuum at 0 flow. This does not seem like very much to me. I would find out what the requirements of the printing frame are.

These are supposed to be good miniature pumps; are you sure the 5-series is too weak? The outlet part seems pretty stong.

Changing the inlet to small diameter nipples will give you more vacuum at the nipple because the air would have to speed up in order to maintain mass flow. Now that I see what you are doing I would leave that part alone. You should let the end process be the restriction.

That's good. I'll try hooking up twin poly tubing at the inlets and see whether I can suck the air out of something. (Perhaps my head.)

 

[Poptart]

The pump from an old refrig will pull 27.5" to 29" of vacuum.

I've used many of them to pump down auto A/C systems.

That's what a Mother Earth article recommended--the hermetically sealed type of the old frige compressors. I haven't gone looking for one yet, but I may.

 

[Poptart]

Poptart,
If you're close to the NYC area, I can lend you a vacuum pump. Otherwise, it'd be pricey to ship.
-Nick

Alas, Colorado. But thanks.