vacuum pumps

[cavalier2903]

I need to invest in a vacuum pump i work on equipment from refigeration to light commercial about 20 tons at the top end. i have heard that an oversized pump is a waste of money. so should i get like a 6 cfm pump or should i go bigger or smaller. i cannnot find any definitive answers on the net as to how to determine what cfm size pump to use. anybody have an answer for me or a reccomendation on a good pump. i have been looking at the jb industries platinum 2 stage 10 cfm but am starting to think its overkill

[FEISTY]

I can tell you from both sides of the counter that , in MY opinion, J B is the leader in dependable, long lasting and affordable vacuum pumps. No fancy plastic parts or shell pieces, great over the counter warranty policy and worth it if you need to send it back for factory rebuild. I carry 2 - 7cfm Platinum Series units on both of my trucks. They are more than adequate for 99% of daily use. Put both on same system if you need extra kick and that's that. Just my thought. Just remember...especially with the blend *****s, change the oil more than you think it needs to be. Everything will work better and last longer.

[Magoo]

At last count I have four vac pumps, two 15cfm, one 25 cfm and one 5 cfm capacity.
For large systems I use multi, vac pumps. For small systems the baby one. My criteria is weight and lugabilty.
The critical thing though is oil quality and performance. Run the pump on a vac gauge to establish real capacity of pump. [ 120 microns or better ] the suck factor.
The cfm rating is free air capacity. Remember to keep the connecting hoses/pipes between pump and system, as big and as short as possible to be totally efficient and time effective. On new all systems treble evacuate.

[FEISTY]

Hey Magoo...what did you pay for the 25 cfm unit ?? Here in US a 10cfm pump is considered lab quality and is more than my last wife got in alimony.

[jhd1234]

I had JB pumps as well and was very satisfied with them
for the size systems you are talking about, 6cfm would be good.
my policy was to change the oil with every job it realy prolongs the pumps life

[Tesla]

Hi Magoo
Sorry to dissagree, but I found from working on perhaps slightly bigger equipment (2mW centriffs) - that a pump that pulled 50 microns was insufficient, one that pulled 25 was good and a new one after the 48 hours run in time pulled 17.

[cavalier2903]

so what ive heard is for sure a jb pump i can go with that but stiil dont know what is the benifit of a larger cfm pump unless of course work is being done on industrial equipment doesnt the cfm rating only really matter while its in first stage

[mad fridgie]

so what ive heard is for sure a jb pump i can go with that but stiil dont know what is the benifit of a larger cfm pump unless of course work is being done on industrial equipment doesnt the cfm rating only really matter while its in first stage
The size of the pump refers to FAD "Free Air Delievered" This has no relation to what vacuum can be drawn.
A vaccum pump it could be said has 3 main uses
1; Leak detection
2; Removal of non condensables
3; Vapourizing of free water

If we take "2" in a well installed system (always capped, purged with nitrogen) the size will determine the length of the vac process, bigger the machine shorter the time. The same could apply for "3" but when dealing with free water, ambient temperature comes into play, Lower the temp, the deeper the vacuum required to vapourize, and the greater the volume that needs to be pumped for a fixed mass of water (density of water vapour at low pressures and temperatures)
So in breif, warmer climate smaller vac pump,
colder climate larger vacuum pump.

Example (not real figures) (i normally work in metric)
System has 1Lb of water in at 100F, occupies 100 cuft
System has 1Lb of water in at 50F, occupies 500 cuft.
Then you would at least need a vacuum pump 5 timer bigger for the second system to achieve the same time for each system. Example only