Vacuum Pump sizing

[leakcheck]

I was wondering if anyone has a reference chart for vacuum pump sizing based on system size to cfm pump size and/ or a complete list of positive / negative effects oversizing and undersizing might have .


Thanks alot, Rob


P.S. just got a dv22n JB micron gauge and found my pump is only pulling down to 600 microns with new oil and would like to replace is reason for this post. Employer is mad at me for wanting them to replace a 1994 pump thats never been rebuilt and is telling me im trying to be too accurate with my job.

[icemeister]

Here's what J/B Industries has to say about sizing vacuum pumps:

Pumps in the 1-1/2 to 10 CFM class are adequate
to handle 99% of our work. As a rule of thumb, the CFM
rating squared equals the maximum system tonnage. A
7 CFM pump is rated for 49 tons; 3 CFM pump is rated
for 9 tons. They are all that should be purchased for
service and installation. In many cases, depending on
the system line sizes of large tonnage systems, it is
better to put two or more of the small, easily handled
pumps at different locations. This will overcome some of
the pressure drop problems and actually be faster than
a single large pump.

Here's a link to the the full article (Lot's of good info in there):

http://www.jbind.com/tools/userfiles...Principles.pdf

[leakcheck]

Thanks alot I will read the article.

[gatorfan9606]

I was wondering if anyone has a reference chart for vacuum pump sizing based on system size to cfm pump size and/ or a complete list of positive / negative effects oversizing and undersizing might have .


Thanks alot, Rob


P.S. just got a dv22n JB micron gauge and found my pump is only pulling down to 600 microns with new oil and would like to replace is reason for this post. Employer is mad at me for wanting them to replace a 1994 pump thats never been rebuilt and is telling me im trying to be too accurate with my job.

if your only pulling down to 600 there something wrong with the pump

[zw17]

Just remember... When it comes to vacuum pumps, bigger is not always better. Dehydrating a system is a slow process and takes a lot of time. Most jobs can easily be done with a good 5cfm pump.

[yellowirenut]

i had a dream i was working (ugg what happened to the dreams of naked chicks)
and i hooked up two vacuum pumps. If you are working on a lager system would hooking up two pumps would it be a help or a hinder? say one on the evaporator and the other near the compressor.

[stanbyyourword]

if you can isolate high and low sides fine , if not you risk the stronger pump over coming the other and pulling in air through weaker or lesser, learned this the hard way regards stan

[local 832s]

Only 600 microns, you may not have a tight system. Double check your joints,evap,cond,compressor, ect... Or the pump could be not working properly. To big of a pump can cause moisture to freeze in the system causing you to chase your tail when pulling it down. Best to go slow and steady.

[yellowirenut]

if you can isolate high and low sides fine , if not you risk the stronger pump over coming the other and pulling in air through weaker or lesser, learned this the hard way regards stan

that is what i thought may happen..even thought both rated at same CFM i am sure one may be pulling harder than the other. Thanks

[IceMonster]

Just my ten cents worth to add for the evacuation process.
1) I love the core removal tools (Remove those schrader cores)
2) No low loss fittings
3) I use 3/8 to 1/4 evacuation hose not those manifold gauge hoses.
Bottom line: you can take a 2 or 3 cfm pump and do outstanding job so long you have no limitation through valves and hoses etc.... Happy evacuations

[leakcheck]

Hey Icemonster what 3/8 to 1/4 hose are you refering to? I purchased a new pump 15600 6 CFM robinair that does a great job. Plus i found out my yellow jacket hoses have tiny tiny holes in the somehow. So was thinking of investing in a 4 valve manifold for the 3/8" hose. Any input welcome please.

[Marc O'Brien]

if you can isolate high and low sides fine , if not you risk the stronger pump over coming the other and pulling in air through weaker or lesser, learned this the hard way regards stan

I can't see this happening. Maybe if one pump is off. But then the same would happen with a pump off even if there wasn't another pump connected.

It's okay, in fact recommended, to put as many pumps on as you can unless you know there is free water in the system which could freeze and rupture piping or components if the total vacuuming power is too great. Keep in mind, if there is free water in the system then even a small vac pump can freeze an amount of water enough to also cause damage.

[seraaco]

Hi all
How can water get frezze in a system with such deep vacuum? all i know is that in vacuum water boiling temperature point can be lowered,( athmospheric pressure 212 f) but how can the water boil inside the system and freeze at the same time? if the system has water inside and it's frost it can pass to vapor directly and it's called sublimation (in vaccum ), but I havent heard we can get water frezee when boiling, not inside the system.