7 cfm vacuum pump
looking for thoughts on 7 cfm vacuum pump for residential. I can get a 7 cfm JB pump cheaper than 5 cfm just looking for opinions. Wondering if 7cfm is to large maybe some frezzing issues of the moisture. Thanks for the info.
I would be looking at the bottom line. If I could get a bigger one for a less money, fine.
But as far as the capacity goes, just remember, no mater how big the pump is, it's still pulling gas through a very small hole. A hole that only allows "X" amount of air through it.
So it boils down to dollars.
Have fun, good luck,
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7cfm means it's good for starting the pull--when you have a lot of cf to move. But what does it mean when it comes to pulling and maintaining a high vacuum? Nada.
The only reason to buy a higher cfm pump is if you want to pull a vacuum on a larger system.
Vacuum pumps for AC/R are rotary vane pumps:
As the rotor turns, the vanes on the rotor constantly aerate the oil with refrigerant, as if the pump was trying to make whipped cream.
If you talk to a vacuum pump maker such as Laco (http://www.lacotech.com/vacuumtechno...cuumpumps.aspx), they will tell you that vacuum pumps made for AC/R are low end pumps, because they are often abused and thrown away. The cheaper the pump, the more likely it was built with cheap components. You get what you pay for.
Vacuum pump oil is designed to work well with ref systems. It's a low vapor pressure, high purity oil. It's not designed to hold up well in vacuum pumps. It mixes with water vapor and other CRAPP, and quickly loses its ability to lubricate components and to maintain a good seal. You can't tell how much it has degraded by looking at it. Contaminants and component friction ruin vanes, seals, and sometimes other interior surfaces.
High pressure also causes oil to mix readily with contaminants. That's what the ballast valve is for. Failure to use the ballast valve will degrade the oil.
If your pull is taking a long time, it's because
1. The system has a leak.
2. You are using small hoses and fittings.
3. You are using leaky hoses or fittings.
4. Your vacuum pump oil is full of refrigerant and contaminants.
5. Your vacuum pump has worn parts.
Vacuum pump oil should be replaced after pulling a vacuum on one or two systems. Get in the habit of changing it on a daily basis when you have been pulling vacuums (if you haven't already). Failure to frequently change vacuum pump oil is what causes poor vacuum pump performance and shortens vacuum pump life.
Do you want a pump that will run 24/7? Do you want a pump with high quality stainless steel parts? Do you want a pump that's easy to rebuild? You won't find one for the price you want to pay.
Do you want a pump that will continue to pull a decent vacuum over the years? Change the oil.
A pump whose selling points are low price and high cfm is appealing for all the wrong reasons.
Last edited by beenthere; 05-11-2012 at 02:02 PM.
Reason: as per OP request.
CRUD = Contamination Resulting in Undesirable Deposits.
CRAPP = Contamination Resulting in Additional Partial Pressure.
Change your vacuum pump oil now.
Test. Testing, 1,2,3.
synthetic vacuum pump oils claim 10x life vs std oils.
has anyone tried synthetic pump oils?
I have not tried the synthetic oils. It seems overkill if your policy is to change oil every pump down. In my experience changing oil after every pump down has a good return on investment. To try and use the same oil after a few system vacs costs the customer much more and coincidentally upsets folks.
You could of course just not charge the customer for the time of vac pumping and use the same oil for multiple pump downs but in the end it wears more on your pump. Despite it looking brand new and clean its best to simply change oil ea. time and build that into your estimate.
Didn't even know they were available. Not so sure it's worth any extra money just for the "synthetic" label. Good quality oil should be more than appropriate. Another thing to remember is a 7cfm isn't gonna do any better job then a, say 3cfm, on a 4ton resi split, but it sure will hold more oil. At the end of the week you might have gone through a heck of a lot more oil.
Originally Posted by cy
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I think the jb pumps are a good deal. Which one is it. Just so you know some do not come with blank off valve.
i learned something from one of our mods a while back about residential pumps....he stated that a 1.5cfm pump would do the job on most any resi work we would do..there is no need to lug a 7 cfm around...most pumps that size i've seen were mounted on wheels & used for large centrifugal systems , and the point about the amount of oil used per change is also valid.....Jack
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Could the difference in price be because the 7 CFM is a single stage pump and the 5 CFM is a 2 stage? You will want a 2 stage pump. You won't have any need for anything over 5 CFM 2 stage on resi and small commercial.
Originally Posted by shaworth1
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CFM of the pump itself doesn't matter as much as the entire evacuation setup.
If you're using a 7 or even a 10 CFM pump and evacuating through a 1/4" hose with schraeder fittings, you will NOT see any benefit from the larger pump.
Use large bore, vacuum rated hoses, remove the schraeder fittings and a vacuum tree at the pump and you can see benefit from larger pumps.
The pump im wondering about is a JB DV200N. It is a 2 stage pump and does have an isolation valve. The reason im asking is i get a pretty good discount with grainger and they can give me a good deal on this pump.
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I can't remember where I read it, but I've been told, and I believe it to be accurate, that a 1/4" hose flows approxiately 0.6 (6 tenths) of a CFM.
Originally Posted by jmac00