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Help choosing a vacuum pump...

 
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TK161
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PostPosted: Wed Mar 15, 2006 12:19 pm    Post subject: Help choosing a vacuum pump... Reply with quote

I'm trying to find a vacuum pump and I'm not sure about the micron rating. What micron rating would I need to be equal to 25" Hg? I'm looking at the Robinair pumps. Robinair seemed to be reasonably priced on ebay. Does anybody have a model # that they know will work?

Thanks,
Randy
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PostPosted: Sat Mar 18, 2006 6:20 pm    Post subject: Re: Help choosing a vacuum pump... Reply with quote

TK161 wrote:
I'm trying to find a vacuum pump and I'm not sure about the micron rating. What micron rating would I need to be equal to 25" Hg? I'm looking at the Robinair pumps. Robinair seemed to be reasonably priced on ebay. Does anybody have a model # that they know will work?

Thanks,
Randy


Hi Randy!

I do heating, refrigeration and air conditioning for a living and I use vacuum pumps all the time, so let me explain how "vacuum" is measured here on earth. TRUE vacuum is only attainable in outerspace, because in fact it IS vacuum.... 0"Hg.

Here on earth our planet has an atmosphere, so think of it as the ocean. The deeper you go the higher the pressure gets, you with me? For us land dwellers, "Sea Level" IS the bottom of OUR ocean. Our atmoshere, even though made up of various gases (some better smelling than others, LOL) has mass, therefore weight. All this weight from the fringes of outerspace to sea level pushes downwards and the force it exerts on us is 15psi (rounded off).

We measure this pressure in "inches of mercury" with a barometer. The barometer is a glass tube about 36" long that is closed at one end and filled with mercury. It is then inserted open-side down into a puddle of mercury and held upright. The mercury will try to run down into the puddle, but it will not run out. The atmosphere is pushing down on the puddle, and a vacuum is formed in the top of the tube. The mercury will fall to 29.92" (from the original 36") at sea level when the surrounding atmospheric tempurature is 59*F, aka standard conditions.

As you lower the atmospheric pressure the further the mercury will "fall" hence the term, "inches of mercury" also expressed as " Hg. Now onto your question (unbelievable I know, LOL) At 25"Hg you are not into the micron range as you are short 4.92"Hg from 29.92".

One micron is one MILLIONTH of a MILLITMETER! I work with pumps that will pull a "vacuum" down to about 50 microns if you let them run long enough. I traded Jim an armor set for a Hi-Vac pump, and THAT baby will pull down a 40 gallon tank (that has minimal moisture in it) down to around 29"Hg in about 2 minutes or so! (I timed it!)

Look at the illustration below and apply what I said and you will see how microns fit into all of this!

Here is an eBay link to a vacuum pump and is the same I traded with Jim, but his is red. It's an EXCELLENT vacuum pump and will last for YEARS! The price on this one is so danged good that I'd buy this one RIGHT NOW myself if I didn't already have an excellent 10CFM pump sitting out in my work shop. Hope this helps!! Very Happy

http://cgi.ebay.com/ROBINAIR-6-CFM-High-Performance-VACUUM-PUMP_W0QQitemZ7600399178QQcategoryZ46548QQrdZ1QQcmdZViewItem


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Mattax
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PostPosted: Sat Mar 18, 2006 8:08 pm    Post subject: Reply with quote

Quote:
I do heating, refrigeration and air conditioning for a living and I use vacuum pumps all the time


Since you do this can you tell me where to obtain BOC Edwards certified parts for my E2M28 Vac Pump? I need all the inlet and outlet filters (moisture and oil vapor).

Thanks.
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Mattax
TK487
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PostPosted: Sat Mar 18, 2006 9:58 pm    Post subject: Reply with quote

Hey Mattax,

I just looked up that pump on their website, and THAT is one snazzy pump! I bet you average around 20CFM give or take on the conditions!

Although I don't use anything THAT high-end, the best I could come up with for your area are these guys, Scientific Instruments Services, in NJ. Just enter in your pump model in the search bar in the upper left and it will point you to the filter kits for that pump.

http://www.sisweb.com/

If they can't square you away, then try the contact page of BOC Edwards, they have a LOT of USA/International contacts you can try out!

http://www.bocedwards.com/index.cfm?locations/con_loc_sel.cfm~content

Hope that helps!!
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Mattax
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PostPosted: Sat Mar 18, 2006 10:17 pm    Post subject: Reply with quote

Very much thanks!
On both counts... Very Happy

Edwards Small Pump Filter Kit is $334.

And I would still need the moisture filter kit which is not shown on their website. Damn money pit. I can't see the bottom yet!
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Mattax
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PostPosted: Sun Mar 19, 2006 12:39 am    Post subject: Reply with quote

What praytell are you using this pump for, just vac-forming? If you are then you sure don't need to spent that kind of money on filtration! All that stuff is for operation in EXTREME CONTROLLED environments where ALL variables MUST be controlled. I would just get a "bowl trap" setup similar to what Crashman is using on the intake side of the pump, OR you could skip the filters and just change out the oil every now and then so the insides of the pump won't corrode. Either way should suit your purposes for vac-forming. Very Happy
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Mattax
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PostPosted: Sun Mar 19, 2006 1:05 am    Post subject: Reply with quote

You are most likely right. Overkill? Perhaps.

However, doing the exhaust oil mist filter is for both reasons of money already spent on the vac system to prolong its life and for keeping the oil from misting my wooden shed or yard (if it were plumbed outside).

No offense to Crashmans setup (I already discussed this with him) but I want to use parts designed specifically for the Edwards pump.

I will have to contact a BOC Edwards rep at the link provided for everything else.

And lastly, yes, it is just used for vac forming but on a larger turn out scale.

I posted this earlier: I was going for a precision frame with a shop vac set up with the option of upgrading later. But once I found out they would not pull down ABS, I had to change to the vac pump system set up. 95% of what I will be pulling will be ABS.

Don't get me wrong, I do appreciate your comments. This forum has been very helpful and continues to be so. Just the route I am taking is one of precision and refinement on a professional set up for 1/3 the cost of the low end professional machine of the same size and caliper. I previously priced them around $17K. I plan on cranking out finished product.
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TK161
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PostPosted: Mon Mar 20, 2006 7:10 am    Post subject: Reply with quote

Thanks, TK4063. I picked up the pump you suggested on ebay. Also thanks for the info. It was s great help. Now the search begins for a tank.

Randy
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PostPosted: Mon Mar 20, 2006 9:20 am    Post subject: Reply with quote

Randy, Cool Beans!! Glad I could help! Very Happy
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Tony Krewson
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jegner
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PostPosted: Mon Mar 20, 2006 2:15 pm    Post subject: Reply with quote

Tony knows his stuff, and his expertise is much appreciated! And yes, I'm still looking for that cheap 30 gallon tank. LOL. But, I did get some valves, and pipe fittings.

Mattax, what sort of stuff are you planning on vac-forming, if you don't mind me asking? Sounds like a big operation!
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Mattax
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PostPosted: Mon Mar 20, 2006 2:46 pm    Post subject: Reply with quote

Other than the costuming, I plan on making custom auto parts.
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