Vacuum pumps question revisited!

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blufive

Sr Member
I'm considering using a vacuum pump to deair my RTV and to possibly use while casting. What sort of pump do you use?

I already have the little red one from Harbor Freight but I don't know if it'll pull enough air fast enough.
 

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Jedirick

Sr Member
RPF PREMIUM MEMBER
I've seen people deair silicone with a 1 gallon empty paint can and one of those inexpensive pistol grip plastic vac pumps. Look for the one that has a built in gauge.

With RTV I don't think time is of the essence as much as ability to pull atmospheres.

If you are talking about the red pump from harborfreight that you hook up to a compressor I think it pulls between 28 and 29.

When you say "and to possibly use while casting" if you mean setting resin in a RTV mold then I would think you would want to use pressure not vaccum.
 

exoray

Master Member
Originally posted by Jedirick@Feb 13 2006, 10:11 PM
If you are talking about the red pump from harborfreight that you hook up to a compressor I think it pulls between 28 and 29.
With the HF venturi, I can get about 27/28 inches on my big compressor in the garage, with a smaller compressor that I have in the house I only get about 23/24 inches... So real world results will vary depending on your compressor and the volume of air it supplies...

Without spending a fortune you won't get much more speed on the pull then the HF one does, but you might get a little better vacuum... Try a Google search (or ebay) for Gast brand vacuum pumps... You can also go on the cheap and rip one out of an old fridge or freezer but results will vary and you will need to probably put an oil blocker inline...
 

TheSt.LouisKid

Sr Member
One shop I worked out of bought a vac pump from a auto parts supply store. Its used to vacuum out radiators or something. Its been awhile so I can't remember exactly what its used for. I imagine if you called and asked around you could get more info. Supposed to cost a few hundred less.
 

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blufive

Sr Member
Originally posted by Rylo@Feb 14 2006, 01:25 AM
Doug, didn't you get my Hi-vac?
[snapback]1183848[/snapback]​
No baby, that bulge in my pants when I left your house was all me.

:D
 

Jimbo890

Well-Known Member
The auto parts store vacuum pump is used to clear brake lines etc. of air. Works great. I have one if anyone wants it, and I have the Red Harbor Freight pump. Both of these I planned to use to test my vacuum forming system, but now don't need them.
 

LeMarchand

Sr Member
Originally posted by blufive+Feb 14 2006, 02:48 PM--><div class='quotetop'>QUOTE(blufive @ Feb 14 2006, 02:48 PM)</div>
<!--QuoteBegin-Rylo
@Feb 14 2006, 01:25 AM
Doug, didn't you get my Hi-vac?
[snapback]1183848[/snapback]​
No baby, that bulge in my pants when I left your house was all me.

:D
[snapback]1183997[/snapback]​
[/b]
I KNEW there was more going on in his workshop than vacforming when i was talking to Rylo on the Phone the other week.....

Marc
 

TheSt.LouisKid

Sr Member
Thats what I'm talkin' about. Damn, I'm gettin' old and memory is getting rusty.


Originally posted by Jimbo890@Feb 14 2006, 02:46 PM
The auto parts store vacuum pump is used to clear brake lines etc. of air. Works great. I have one if anyone wants it, and I have the Red Harbor Freight pump. Both of these I planned to use to test my vacuum forming system, but now don't need them.
[snapback]1184026[/snapback]​
 

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blufive

Sr Member
Thanks for the info, fellas. I'll have to fire up the Harbor Freight one I already have and see how well it works. I'll shoot for the auto parts version if I don't like the first one.

:)
 

blufive

Sr Member
Okay, I bought a 30 gallon compressor and attached my Harbor Freight vacuum pump to my new vacuum chamber.

The Harbor Freight pump requires a constant 90 PSI to maintain the 28-ish inches of mercury. The tank holds 155 PSI and is drained rather quickly. I'd say the air supply dips under 90 PSI in 1-2 minutes and then the vacuum isn't as effective.

Should I look at a different vacuum pump? I'm not opposed to the idea but I don't want to have to buy a larger compressor. I've only had this one for 2 weeks.
 

exoray

Master Member
Originally posted by blufive@Feb 24 2006, 07:51 PM
The Harbor Freight pump requires a constant 90 PSI to maintain the 28-ish inches of mercury.  The tank holds 155 PSI and is drained rather quickly.  I'd say the air supply dips under 90 PSI in 1-2 minutes and then the vacuum isn't as effective.

Should I look at a different vacuum pump?  I'm not opposed to the idea but I don't want to have to buy a larger compressor.  I've only had this one for 2 weeks.
[snapback]1192803[/snapback]​
Put an on/off valve on each side of the HF pump, when the compressor tank drains, close the valve between the pump and tank, and then the valve between pump and air compressor... Let the compressor build back up then open the pump to compressor valve immediatly followed by the pump to tank valve and it should then continue to pull down... Once you get down, and assuming you don't have a leak, closing the valve should hold the vacuum just fine...
 

blufive

Sr Member
I was wondering if closing a valve would hold the vacuum. I figured it would but then again, I wasn't sure if the bubbles would continue to rise with a closed valve.

Then again, I don't think everyone that vacuums RTV has a 60 gallon compressor at their disposal either.

:D
 

exoray

Master Member
Originally posted by blufive@Feb 24 2006, 08:28 PM
I was wondering if closing a valve would hold the vacuum.
[snapback]1192841[/snapback]​
Mine tank holds vacuum fine overnight, with a closed valve... Get the 1/4 turn ones, they make life a lot easier... And if you are around you can always fire up the compressor and bring it back down if it starts to rise after a few hours...

On the flipside it leaks a little while under pressure so I need to leave the compressor hooked up when pressure casting...
 

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terryr

Sr Member
I use the motor from a Fridge. It pulls a high vacuum but takes a while, but then the motor is oil cooled.
 

OhioAstromech

Well-Known Member
<div class='quotetop'>(terryr @ Feb 25 2006, 07:23 AM) [snapback]1193133[/snapback]</div>
I use the motor from a Fridge. It pulls a high vacuum but takes a while, but then the motor is oil cooled.
[/b]
This is the same thing I use for my Vacuum Chamber and it pulls 26 to 27 inches of mercury.

From what I understand 28 inches of mercury is as deep as you can get on earth and it changes depending on altitude.
People in Denver will get a better vacuum then someone in Death Valley.

Scot
 

replicaprops

Official Licensee
RPF PREMIUM MEMBER
if the mold is small enough to fit in your pressure pot, there is no need to vac the rubber. Just cure the mold under pressure and it will have better results than vac.
 

blufive

Sr Member
My vacuum pump goes to 29-30 inches of mercury. The people at Silicones Inc. told me you had to have 29 inches to properly deair RTV.

:)


<div class='quotetop'>(OhioAstromech @ Aug 7 2006, 01:06 PM) [snapback]1295587[/snapback]</div>
<div class='quotetop'>(terryr @ Feb 25 2006, 07:23 AM) [snapback]1193133[/snapback]
I use the motor from a Fridge. It pulls a high vacuum but takes a while, but then the motor is oil cooled.
[/b]
This is the same thing I use for my Vacuum Chamber and it pulls 26 to 27 inches of mercury.

From what I understand 28 inches of mercury is as deep as you can get on earth and it changes depending on altitude.
People in Denver will get a better vacuum then someone in Death Valley.

Scot
[/b][/quote]
 

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