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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / August 2007A/C techs: will a venturi vac pump work well enough for occasional use?
Good day, I was wondering if a venturi (air actuated) vac pump will suffice for pulling 28inHg to evacuate moisture from my A/C system in a project Nissan? I have heard of shadetree mechs using engine vac as well for this task in a pinch. I don't want to rip apart an old fridge nor do I want to shell several hundred bucks out for a decent electric vac pump. Can anyone with experience tell me whether or not these air venturi pumps will work? My compressor in 7HP 70gal with 100% duty cycle so I'm sure it's up to the task for an hour or so. Oh yeah - CFM @ 90 PSI - 10.3 (if that helps)... Thoughts? Thanks, Andrew. I have one of those little venturi vacuum pumps I bought for $20.00 at a pawn shop (I love pawn shops) about 15 years ago.I hooked it up to my aircompressor.(Sears cast iron two cylinder aircompressor) The little vacuum pump doesn't have much of a vacuum.J.W.Whitney will sell you one for $73.99.In my opinion, they are too much money for the amount of bread. cuhulin > Good day, > > I was wondering if a venturi (air actuated) vac pump will suffice for > pulling 28inHg to evacuate moisture from my A/C system in a project Nissan? It will if you have a big enough compressor. I have a venturi vac pump that I have used with success to pull 28+", but it takes everything my 5-horse 220V compressor can throw at it. My little 110V portable won't cut it. My > compressor in 7HP 70gal with 100% duty cycle so I'm sure it's up to the task > for an hour or so. Oh yeah - CFM @ 90 PSI - 10.3 (if that helps)... That should do it if the ratings aren't fudged. My old Sears aircompressor has a 2 horsepower motor, it will pump up to about 140 psi.I think Harbor Freight sells those little venturi vacuum pumps too. cuhulin > My old Sears aircompressor has a 2 horsepower motor, it will pump up to > about 140 psi.I think Harbor Freight sells those little venturi vacuum > pumps too. > cuhulin Doesn't matter how much pressure it can pump up to, it matters how many cubic feet per minute it can deliver *at* over 90 PSI. 2 horsepower won't cut it. And the venturi pump I use is a POS Harbor Freight, and it works fine. Even Harbor Freight can make something as simple as a venturi pump that works. Just don't buy any Harbor Freight tools that actually have moving parts! :-) I never have bought anything from Harbor Freight.I can buy better tools in the pawn shops around here.I remember when I bought my venturi vacuum pump and I got home with it, I looked inside of the houshing, nothing to it but a little venturi tube.I felt like I spent too much money on it.One pawn shop in paticular about four miles from me (it used to be gas station many years ago) you have to be careful when you walk inside because there are tools strewn eveywhere and you might trip over them.That's the kind of old pawn shops I like.I bought a compressed air needle scaler for $10.00 at that pawn shop a few months ago.It works great for knocking off heavy rust. cuhulin > > Good day, > [quoted text clipped - 12 lines] > > That should do it if the ratings aren't fudged. Your compressor meets the requirements to use this part http://www.beachtradingco.com/servlet/the-12610/Air-Vacuum-Pump/Detail. this should pull 29" and it's $33. > Good day, > [quoted text clipped - 8 lines] > > Thoughts? Atmospheric pressure is roughly 760,000 microns. A proper AC evacuation would be to 500-700 microns. Your 28 in.hg. evacuation comes out to be 48768 microns. Not even close, by a bunch. Will it work, will it blow cold? If the moon and stars are aligned right, you replace the receiver/dryer, replace ALL of the oil and minimize the amount of time that the system is exposed to atmosphere, maybe. Forget anything you may have read about water boiling at XX temperature at 28 in.hg. Boiling doesn't mean squat if the moisture isn't being removed. Air venturi vacuum pumps are a joke. > In article <C2F073E1.2517%anix...@REMOVETHEcogecoDOT.ca>, > [quoted text clipped - 16 lines] > Your 28 in.hg. evacuation comes out to be 48768 microns. > Not even close, by a bunch. Last I heard, 28in Hg = 710mm Hg = 94% of atmospheric pressure. Which is pretty impressive for just a tube with a hole in it! Must be madly innefficient though. > Last I heard, 28in Hg = 710mm Hg = 94% of atmospheric pressure. Which > is pretty impressive for just a tube with a hole in it! Must be madly > innefficient though. ANYTHING powered by compressed air is madly inefficient. For starters, as soon as you compress the air, approximately 1/2 of the energy that went into the compressor gets converted into heating the air. Before you use the air it usually cools off again so all that heat energy is lost. 50% efficiency right off the top. THEN you get to start factoring in the losses in the air hoses, the tool iteslf, the compressor belts, motor, etc. All in all, if you get 10% of the energy out of the tool that you put into the compressor, its doing pretty damn good! But people don't use air power because its efficient- air power is good because its rugged. No cooling of the tools is needed, no electrical hazards, dirt and filth tolerant, etc. etc. Venturi vacuum pumps can pull vacuum on very wet or dirty loads that would contaminate the oil and corrode conventional vacuum pumps, so they do have a place in the world. In article <1187797858.234184.241910@r23g2000prd.googlegroups.com>, > > Your 28 in.hg. evacuation comes out to be 48768 microns. > > Not even close, by a bunch. > > Last I heard, 28in Hg = 710mm Hg = 94% of atmospheric pressure. Which > is pretty impressive for just a tube with a hole in it! Must be madly > innefficient though. Impressive is an Inficon Shark vacuum pump that will pull a system down to 25 microns. I wouldn't dream of shipping a car that could only be pulled down to 28 in.hg. |
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