Doing some research on some Vacuum Pumps

General Composites Discussions Products Talk
#26

“Inches of Mercury” is a method for measuring vacuum

Say you have 26.0"/hg…that equals only a 87% Vacuum. That means you still have 13% of the volume as being taken up with Air molecules (ie. that is enough to REALLY screw up an infusion molding)

CFM (Cubic Feet per Minute) is a term for measuring the amount of air flow that a compressor can do. There are 2 basic types…Actual CFM and Displacement CFM

Actual CFM is waht you can actually measure coming out of the compressor in a regular atmosphere. This number changes with air pressure and motor RPM and air line resistance.

Displacement CFM is the volume that the Piston displaces over a full minute. It more theorectical than anything and only changes with motor RPM

Robinair pumps are measured in Microns becasue they can go that far to a deep vacuum. Gast pumps cant go anywhere near there…so they are measured with Inches of Mercury (probably to make them look more impressive by marketers…would you buy something that did a 29"/hg or a 20,000 Micron vacuum :wink: )

Here is a chart to help you see the corelations between all the vacuum scales that are dealt with here.

#27

Great post, Evan put a sticker on that 1!

#28

I can’t claim responsibility for that chart. :stuck_out_tongue: hehe…I just borrowed it from Nandor pumps I keep it always on hand though when I’m looking at pump specs

#29

Thanks Spruce, That is a great post and hopefully I can find something within my $ range.

#30

what the hell does this mean then???
has a vacuum pressure into the 10 to the minus 3 millibar zone

#31

i reckon this should do the trick :lol:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=3868037607&ssPageName=STRK:MEWA:IT

#32

10^-3 millibar = 0.001 millibar = 0.000001 bar

#33

10,000 microns then or 29.5ish mercury,not bad.

#34

Huh? If it is 1x10^-3 millibar, thats about 1 microns.

That Edwards pump you linked, it just said 9.8 x 10^-3, but no units. Without units it’s meaningless. Is it 9.8x10^-3 millibars, which would be closer to 10 microns. Or is it 9.8x10^-3 bars or close to 7600 microns. Or is it absolute pressure in psi or inches of mercury or inches of water… etc, I think you get the idea now.

#35

now youve really confused me :?

#36

I’d buy it if it stays at that price.

Search the 'net for Edwards E1M-18

“Purchased in year 2000 and used in racing car factory for composite production. Without the trolley and ancileries these pumps cost in the region of £2500.”

Shows a guage reading of 29.5"ish.

#37

I looked up the specs for the Edwards E2M18 vacuum pump. It is rated at 1x10^-3 mbar. Which is 0.001 mbar = 0.000001 bar. 1 bar = 1 atm. So this is a 1 microns vacuum pump.

All this stuff is metric, which you are suppose to be familiar with on the other side of the pond. The inches of mercury and psi is an American thing. Looks like someone was day dreaming in class during the lecture on metric units.

#38

:oops: heh heh,i was more into the practical lessons :lol:

#39

well i bought this one-
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=3867206833&ssPageName=STRK:MEWN:IT
i havent recieved it yet,the guy couldnt read the label as its damaged so im not sure which model it is? i reckon i should be able to make a hose and regulator up with all the bits that come with it…

#40

That will work. Ask him if he knows a source for vacuum pump oil for the unit. I would change the oil on a used unit as a 1st step.

#41

They would be laboring for vacuum bagging, cause they run a lng tme. I would use a new one only for bagging. If you do the infusion correctly, you will be sealing the bag first and finding leaks. Then once you start the infusion you want to run it between 15 and 20 and once the infusion is done keep it on til it gels or use a paint pressure pot and make sure it is dropped to about 10

#42

are these pumps not designed to be run for a long time then? looks like i will be giving infusion a go then :slight_smile:

#43

I meant that you can’t rely on them for lots of bagging jobs. they will eventually get worn out and cause you to get a different pump.
They are great for learning and growing a business.

#44

cool,if it lasts for 100 parts then that would be great :slight_smile:

#45

It will last for more than that, it may need some rebuild somewhere near there.

I have several pumps one similar to that for degassing of urethanes and silicon rubbers, one that is made by sargeant welch that is a wet vane system with a 17.5 cfm, and one that is wet vane also made by wlech pump and is about a 1954 vintage that has 35.5 cfm. I have it connected to a 300 gallon tank for my vacuum lines around the shop. I can suck the air down to 29 inches of mercury in about 4.5 minutes with that one.
(I knew a girl like that once)