Vacuum Pump?

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spiritwoodturner

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I've been reading Steve (Stevers) great tutorial about building a pressure/vacuum pot, and find that the vacuum pump he recommended in that article is no longer available. I've written to him privately, and he recommended I ask here. I actually bought this red plastic encased vacuum pump they now have, but it's kinda hunky and I'm not quite sure how I'll mount it to a pot, but it's about all I can find. Steve wondered if the same, smaller, inline pump is inside this contraption, but I just got it today and haven't had a second to look at it yet.

If anyone knows where I might find the one similar to Steve's example, I think it would fit on the pot easier, and would be greatly appreciated.

Thanks,
Dale
 
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I presume you are talking about the "AIR VACUUM PUMP WITH R134A AND R12 CONNECTORS" that Harbor Freight sells. If this is the case, you can disassemble it and use the venturi pump that is inside.
 
That's what I did....disassebled the HF "pump" and took out the venturi valve. It's not really a pump at all. Google "venturi valve" and you'll see the physics behind it. You just need an air compressor and it works great. I built a PV pot almost identical to steves (though I used smaller valves because the big ones like he used are 3 times the price). I just used it last night for a poly stabilizing test. The vacuum on my pot works great, but the pressure causes some air to escape b/c the top only has 4 spots to hold the lid on. I have to put additional C-clamps in place if I want to get over 40 psi.
 
Thanks guys, I think that's the ticket. I'm familiar with the concept, I've got a Holdfast vacuum pump for my reverse chucking of bowls, but can't really use that as it's mounted next to my lathe and has plumbing that won't work for the pot and it's being used constantly anyway. It just didn't dawn on me that HF would repackage it with all the crap around it, but so be it. That's the one I got, Scott, with red plastic housing around it. I'll demolish tonight...

And thanks again, Steve, for writing such a great tutorial on the subject in the first place. Complete with pics, perfect for a genius like me!

Dale
 
Well, Steve, it's close! It has an air inlet, and a vacuum out port, a bypass hole to create vacuum, but no port with screws to take a block out? It's solid, no getting into this little jewel without hacking it in 2. Hey, it was 13 bucks, if it doesn't work it's no big deal. I'll report back right after Christmas when my kids surprise me with my new presssure pot!!!

Thanks,
Dale
 
I too received a red vacuum pump from HF and was told the blue ones have been discontinued. Ended up taking apart the pump and found what appeared to be the same block inside as in the tutorial. Only problem is I never marked which hole was air and which one was vacuum so I haven't hooked it up yet. Not sure if I hook it up wrong will do any damage or not. The little bypass hole that Dale mentioned threw me off.

Thanks, Bill
 
Bill, the holes are pretty easy to tell apart. You see how there's one side that has a threaded hole and nothing else, and the other side has a threaded hole and a smaller non-threaded hole beside it? The side with the threaded hole ONLY is the side you hook the compressor up to, and the other side, the one with the non-threaded hole beside it is the one that draws the vacuum. You can just Google how a Venturi valve works and it will all make sense what's going on inside that little thing. Now, I have the old valve that was in the blue casing, but I'm assuming it's the same concept (Venturi's haven't changed in a while!).
 
OK, I'm confused with the concept of the vacuum setup. What is that V-block thing and how is that used to pull a vacuum? Is that hooked up to an air compressor? I actually have a vacuum pump that my father found (long story), but I'm confused as heck as to how hook the dang thing up to my pot. I have a tiny air compressor that I used for airbrushing my model cars and it looks kind of like that, only bigger. Should I just get one of those V-block things instead? I'm lost.
 
babyblues said:
OK, I'm confused with the concept of the vacuum setup. What is that V-block thing and how is that used to pull a vacuum? Is that hooked up to an air compressor?
Click to expand...

The vacuum "pump" being described here is nothing more than a tube that restricts airflow, and provides an inlet (that, in this case, is used to draw air from the tank) to suck air.

The principle at work is that as the velocity of a fluid increases, its pressure decreases. So, if we take a stream of air (the fluid) and constrict its flow, we force it to speed up in order to fit through the constriction. This increase in velocity causes a drop in pressure - and if we port the tube, air will be sucked in through the port due to the relative low pressure area inside. Now, if we hook up this port to a sealed container (the vacuum tank), air will be sucked out of the tank but not replaced (because it's sealed) and thus a vacuum (well, it ain't a vacuum, but that's a whole 'nuther discussion) is created.

If you want a description that makes sense, Google "venturi effect" and "Bernoulli's Principle" - and you'll know as much as anyone.

Why do I know about this? This effect is part of what makes planes (and thus me) fly :)

Cheers!

Gary
 
Brian, you mentioned you have to add clamps to hold pressure. I cast in my HF pot at 50 psi and have no problems, now. Pull the rubber gasket out of the lid, clean it and the groove in lid, get some "plumbers grease", a silver dollar size tin of almost sticky silicone like "stuff" from local hardware store and apply thin coat to both sides of gasket and re-assemble. Put 30 or 40 psi in pot and spray all fitting with water and dish soap solution. any leaks will blow bubbles like crazy. Retape these with the white teflon tape and check again. After doing this to my pot, I can pressure it up, close valve and 3 days later it will still have good pressure. Might lose 2 or 3 pounds. No extra clamps, just the original 4. Hope this helps.
 
Does anyone have a new link for the vaccuum pump from HF that will work with the pressure pot??? I am looking to set mine up and now want to incorporate both vaccuum and pressure like the one steve has. thanks for the reply.
 
CaptG said:
Brian, you mentioned you have to add clamps to hold pressure. I cast in my HF pot at 50 psi and have no problems, now. Pull the rubber gasket out of the lid, clean it and the groove in lid, get some "plumbers grease", a silver dollar size tin of almost sticky silicone like "stuff" from local hardware store and apply thin coat to both sides of gasket and re-assemble. Put 30 or 40 psi in pot and spray all fitting with water and dish soap solution. any leaks will blow bubbles like crazy. Retape these with the white teflon tape and check again. After doing this to my pot, I can pressure it up, close valve and 3 days later it will still have good pressure. Might lose 2 or 3 pounds. No extra clamps, just the original 4. Hope this helps.
Click to expand...

Thanks Gary, I'll have to give that a shot. Throwing the extra clamps on was the "quick and easy" solution, but it would be nice to have it working right moving foward. Thanks for the tips!:biggrin:
 
JT,

Don't have the link offhand, just search for "vacuum pump", it's the only one they have. It's a big red plastic covered deal, just take it apart (takes 2 minutes) until you get to the little metal block inside. I must say for the 12-15 bucks I paid for it, it seems a bit pricey for that little block and a bunch of debris, but hey, whaddaya gonna do?

Good luck,
Dale
 
Thanks, stopped by HF today and picked one up. Little by little I am getting all the parts to put my pot together. This aught to open a whole new experience up by casting.
 
OK, put my pot together (Steve's pressure/vacuum combo) and after getting the gasket to work with the help of some plumber's grease, it's holding pressure fine.

The problem I'm having is with the vacuum. I can not get it to produce ANY vacuum at ANY input pressure, from zero to 80 lbs. I say that because my Holdfast vacuum pump for my lathe has a "sweet spot" pressure range, and anything above or below that produces little or no vacuum, so I figured I'd try that on this thing. I have that little HF piece of crap on my pot, and I have to wonder if that's the weak link. I have it set up in correct order, I believe, with supply air pressure coming into the end opposite the air bypass hole, with the airflow OUT of the block right next to the bypass. But all I can get is for air to blow into the tank, no suction at all. Does anyone know if I have to modify the vacuum block in any way? I can't see that happening as there is no entry into it, but I'm stumped.

HELP!!!

Dale
 
spiritwoodturner said:
OK, put my pot together (Steve's pressure/vacuum combo) and after getting the gasket to work with the help of some plumber's grease, it's holding pressure fine.

The problem I'm having is with the vacuum. I can not get it to produce ANY vacuum at ANY input pressure, from zero to 80 lbs. I say that because my Holdfast vacuum pump for my lathe has a "sweet spot" pressure range, and anything above or below that produces little or no vacuum, so I figured I'd try that on this thing. I have that little HF piece of crap on my pot, and I have to wonder if that's the weak link. I have it set up in correct order, I believe, with supply air pressure coming into the end opposite the air bypass hole, with the airflow OUT of the block right next to the bypass. But all I can get is for air to blow into the tank, no suction at all. Does anyone know if I have to modify the vacuum block in any way? I can't see that happening as there is no entry into it, but I'm stumped.

HELP!!!

Dale
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Tell me I'm mistaken, but from what I read it sounds like you're using a Holdfast vacuum pump to suck air out through the HF vacuum block.....that's going to give you the opposite effect that you want. The HF "vacuum block" is a Venturi valve, which works with PRESSURE to create vacuum. Keep the block setup the same but use your air compressor to blow into it rather than your Holdfast.

If you want to use your Holdfast pump, you don't need the HF vacuum block, since the holdfast is already a vacuum. The HF block is only to "convert" pressure from an air compressor into a vacuum draw. I think that might be your problem.:redface:
 
GouletPens said:
Tell me I'm mistaken, but from what I read it sounds like you're using a Holdfast vacuum pump to suck air out through the HF vacuum block.....that's going to give you the opposite effect that you want. The HF "vacuum block" is a Venturi valve, which works with PRESSURE to create vacuum. Keep the block setup the same but use your air compressor to blow into it rather than your Holdfast.

If you want to use your Holdfast pump, you don't need the HF vacuum block, since the holdfast is already a vacuum. The HF block is only to "convert" pressure from an air compressor into a vacuum draw. I think that might be your problem.:redface:
Click to expand...

Uh, no, I'm not using my Holdfast vacuum pump to operate my HF vacuum pump. I used that as an example only of how input pressure may be affecting how my HF pump may or may no be working. I'm fully aware of the principle of these things, my pot vacuum setup simply isn't drawing vacuum. At any input pressure.


Dale
 
Hey Dale,
Below is a picture of my vacuum pump. The arrow shows me which way the air passed through so I wouldn't forget and install it backwards.

Just to be clear, you are doing the fallowing?

1)hook up air supply
2)open gate valve between the vacuum block and the tank
3)activate air flow
4)monitor vacuum increase
5)as soon as vacuum is reached, "close valve". This traps the vacuum in the tank.
6)then you can turn off and remove the air supply

If this doesn't help, PM me.
 

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I marked airflow before I installed it, but I guess it wouldn't be the first time I had a brain cramp and marked it wrong. I can't quite see it on yours, but my exhaust/bypass port is on the side the arrow is pointing to. Is that right? It really has to be, I believe, from my Aviation Physics degree studies! The bypass air cannot make a 180 and blow back toward the airflow. I do think it's possible this block is faulty. I have to include that when I took the long 1/4" tube off (it was 4" long-didn't want it hanging out that far to get busted off), the thread for the nipple at Home Depot was not exactly the same, and it cross-threaded a tad and cracked a tiny bit of the block edge off. I Jeld-Wen'd it in, it's not leaking, but I'm left to wonder if it cracked on the inside of the block, out of view.

At any rate, all I get is positive pressure on my 2-way vacuum gauge, not negative, and I tested the thing by holding the lid alone in my lap while introducing pressure 10 lbs. at a time, feeling under the opening to see if any vacuum developed. It never has. You shouldn't need the pressure side at all to test that. I figure the only thing left is to pick up another pump at HF and try again. They're cheap enough and I have one close. I think this time I'll leave that long tube on this time and just hook the quick-connect up to that before I try to take that off again. I'll report back to the group if that's the problem, as I think that could be a common problem with others.

Thanks, Steve, I really hope you're doing better. Sorry you didn't get your steak at the Hospital! Although if your Hospital was like some of the ones I was in after my plane crash, it was probably dog or yak instead of cow!

Be well,
Dale
 
spiritwoodturner said:
I marked airflow before I installed it, but I guess it wouldn't be the first time I had a brain cramp and marked it wrong. I can't quite see it on yours, but my exhaust/bypass port is on the side the arrow is pointing to. Is that right? It really has to be, I believe, from my Aviation Physics degree studies! The bypass air cannot make a 180 and blow back toward the airflow. I do think it's possible this block is faulty. I have to include that when I took the long 1/4" tube off (it was 4" long-didn't want it hanging out that far to get busted off), the thread for the nipple at Home Depot was not exactly the same, and it cross-threaded a tad and cracked a tiny bit of the block edge off. I Jeld-Wen'd it in, it's not leaking, but I'm left to wonder if it cracked on the inside of the block, out of view.

At any rate, all I get is positive pressure on my 2-way vacuum gauge, not negative, and I tested the thing by holding the lid alone in my lap while introducing pressure 10 lbs. at a time, feeling under the opening to see if any vacuum developed. It never has. You shouldn't need the pressure side at all to test that. I figure the only thing left is to pick up another pump at HF and try again. They're cheap enough and I have one close. I think this time I'll leave that long tube on this time and just hook the quick-connect up to that before I try to take that off again. I'll report back to the group if that's the problem, as I think that could be a common problem with others.

Thanks, Steve, I really hope you're doing better. Sorry you didn't get your steak at the Hospital! Although if your Hospital was like some of the ones I was in after my plane crash, it was probably dog or yak instead of cow!

Be well,
Dale
Click to expand...

I did "Exactly" the same thing. Mine is repaired with 5 minute epoxy.

This is a photo from the end. Let me know.
 

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That concerns me, because if yours works not sure why mine doesn't. And mine is hooked up exactly like your pic. Steve, do you pull vacuum at a particular input pressure range? Like I said, my Holdfast requires this (although you can't damage it if it's too high), not sure if these need this too, although I've tried it at about every range. I also wonder if these things have a flimsy diaphram that I may have blown up when I first ran it. I probably had my normal 120 lbs. from my compressor go through it.

Puzzling...

Dale
 
There is no diaphragm. It's just a series of ports that force the air to be pulled out of the tank. I don't know how to explain it.
And the pressure should have nothing (or little) to do with it. If you have a little pressure (50 or 60 psi), you will get less vacuum, say only 10 or 12 inches. If you have good pressure (95 or 105 psi), you will get better vacuum, I can pull 21 1/2 inches on a good day.
I don't understand why yours wont work. The venturi block is fairly full proof also.

I wish you could show us what you are doing. Could you at leaste send me a close up picture. If you PM me, I'll send you my e-mail.
 
Does this show you anything? It's very basic and not to scale. The ports are most likely sized diff to allow the venturi affect. But it's a general idea.
 

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Hey Steve,

VOILA!!! Success!!! I went and got a new unit at HF, and if I would have paid closer attention to your tutorial I would have saved myself some time and headache. I believe you said to use the brass fitting at the input end that came with the kit. Well, when I went to take the new one apart, I noticed the brass fitting that comes with the kit has an airflow reduction tube built into it. I believe this piece is ESSENTIAL to it working correctly, as I threw it away from the first try. That, or I somehow damaged it inside with the crossthread situation, but either way, I'm pulling 22 lbs. (is that enough?) and life is good!

Your diagram isn't exactly how I envisioned it, but close enough to get the point. I had it hooked up correctly, the 2 potential problem spots were that brass fitting or my cracking the edge, although I don't believe I did enough damage to it for that to be the case.

At any rate, for anyone reading Steve's outstanding tutorial, don't be a dope like me, read the whole thing, don't do anything differently, make sure you do use the brass nipple fitting that comes on the input side, and be very careful and give some thought before removing and replacing the 4" long nipple that comes with the unit with a close nipple. It has some funky Chinese threading and it could get you in trouble, unless you're a metal threading guy or gal (I'm not). I do know they applied some adhesive on the block end that complicates the matter, because the threading on the other side is fine.

Steve, many, many thanks, and I hope I didn't pull you away too much from USC's drubbing of Penn State! Man, I was looking for a good game today and it did NOT happen. The Bugs Bunny marathon on Cartoon Network has more drama!

Gratefully,
Dale

P.S. It did not act like my Holdfast as far as a "sweet spot" of pressure goes, as you indicated. It seemed to pull more vacuum the more I increased pressure, until about 110 lbs. where it seemed to produce diminishing returns. I figured 22 lbs was about the max, but I could not reach that at 80 lbs. If you pump 110 lbs. into my Holdfast, you get zero vacuum. You get max vacuum at about 40-50 lbs. Just interesting how they work differently.
 
Good for you. Happy to help.
I had forgotten about the brass fitting. It is essential for proper operation. Have fun and happy casting.

Oh and 22 inches is right at the best. You can only pull 23, and that's under laboratory conditions. 23 would be absolute vacuum. It is pretty much impossible for a layman like us.
 
It's going to be quite a while before I get into casting, but when I was at HF today I looked at that vacuum pump and I noticed that the box says it needs 4.2 SCF at 90 psi. I'm curious as to how sensitive it is, if your compressor only is rated at 2.4 or so would it still work, just not pull as much vacuum?

Inquiring minds want to know.

Steve
 
Steve, I have an 8.5 cfm compressor, but my sense is if a compressor can produce 100 psi, you could draw vacuum until you ran out of capacity, shut the valve behind it off, let the compressor recharge (having unhooked from the pot), rehook and quickly draw some more, and do that until you got to 20-22 lbs. of vacuum. It shouldn't take but a few minutes, and it's entirely possible your compressor could handle it in one shot. Steve (Stevers) would know better than I would.

Of course, there's no substitute for a bigass compressor!

Dale
 
spiritwoodturner said:
Steve, I have an 8.5 cfm compressor, but my sense is if a compressor can produce 100 psi, you could draw vacuum until you ran out of capacity, shut the valve behind it off, let the compressor recharge (having unhooked from the pot), rehook and quickly draw some more, and do that until you got to 20-22 lbs. of vacuum. It shouldn't take but a few minutes, and it's entirely possible your compressor could handle it in one shot. Steve (Stevers) would know better than I would.

Of course, there's no substitute for a bigass compressor!

Dale
Click to expand...

DUHHHH!!! :)redface: For some reason it never occurred to me that you could start and stop the process. Makes perfect sense now. Excuse me while I go and slap myself around the room for a while.

Steve
 
Hey, Steve, I found that out totally by accident! I was testing the pressure ranges, and thought, "Hey, I don't have to start over from zero each time, I can just close the valve behind the vacuum and pick up where I left off". Even my 8.5 cfm compressor couldn't keep up with the 10 minutes it took to complete my testing, so I just did it in stages.

My pot's been holding steady at 70 lbs. for a day and a half now! I have my resin, just need my molds from Matt and I'll be ready to play!!!

Dale
 
Awesome Dale. If you can hold a set pressure for 24 hours, your good to go. Personally, I don't like to leave my air supply connected to my pot. I would rather charge up the tank and disconnect the air line. So being able to hold a set pressure was important to me. The reason for this is that I don't like the idea of leaving my compressor plugged in without me being there.
Sounds like you've got it all ready to go. You'll have to be sure and let us know when you get your first casting done. That first one is always special.
 
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