CAMheads CNC Router Forum By: CAMaster CNC

Go Back   CAMheads CNC Router Forum By: CAMaster CNC > New CNC Setup. > Vacuum, work holding, dust collection

Reply
 
Thread Tools Display Modes
  #1  
Old 12-12-2016, 10:45 PM
de5 de5 is offline
Cobra Owner
 
Join Date: Jan 2011
Location: Honea Path, SC
Posts: 913
Default Adding a 2nd vacuum pump

I use a gasketed vacuum fixture and am running a Gast 3040 V115A oiless pump. It is rated at 25 cfm and 20"hg. Usually this pump pulls between 15" and 20" on my parts which is fine for my needs. However, occasionally I have enough leaks that the vacuum drops below 15", and then the hold down can get iffy depending on the size of the parts. I am thinking about adding another pump just like this one so that when the vacuum is low, I can switch on the 2nd pump to overcome the leaks. So, my question is: if my vacuum has dropped to, say, 10"hg, and I turn on another 25 cfm pump, do you think that should be enough to bring the vacuum back up over 15". It seems feasible to me, but I just thought I would throw it out here for your thoughts.

Thanks,
Charlie
__________________
Charlie Hind
Cobra 404 ATC with 12 tool positions & 4th Axis (2012-present)
(2006-2012 - K2 CNC... sold in 2012 to buy the Cobra)
WinCNC
www.hindocarina.com
http://facebook.com/hindocarina
Reply With Quote
  #2  
Old 12-12-2016, 11:14 PM
Gary Campbell's Avatar
Gary Campbell Gary Campbell is online now
CNC Tech & Trainer
 
Join Date: Dec 2012
Location: Marquette, MI USA
Posts: 2,733
Default

Charlie...
You should be able to get a pretty close guess by looking over the flow charts for the two pumps. Look at your existing and see what the flow is when the vac drops to 12-14. Then see what the other one is pulling at that flow.

Make sure you have a check valve between the two pumps.
__________________
Gary Campbell
CNC Technology and Training
The Ultimate Woodworking Machine
GCnC411@gmail.com
https://www.youtube.com/user/Islaww1/videos

"There are 10 kinds of people in the world. Those that understand binary logic, and those who don't"
Reply With Quote
  #3  
Old 12-12-2016, 11:29 PM
de5 de5 is offline
Cobra Owner
 
Join Date: Jan 2011
Location: Honea Path, SC
Posts: 913
Default

Thanks Gary, I wouldn't have thought of that. Both pumps will be identical, and the flow chart is below. It looks to me like when the 1st pump drops to 10"hg, it will be moving about 15 cfm. So does that mean that when I turn on the 2nd pump, it will raise the vacuum by 10"? I'm using the bottom line for my rpm.
Attached Images
File Type: jpg Capture_3040.JPG (76.8 KB, 26 views)
__________________
Charlie Hind
Cobra 404 ATC with 12 tool positions & 4th Axis (2012-present)
(2006-2012 - K2 CNC... sold in 2012 to buy the Cobra)
WinCNC
www.hindocarina.com
http://facebook.com/hindocarina

Last edited by de5; 12-12-2016 at 11:55 PM.
Reply With Quote
  #4  
Old 12-13-2016, 06:57 AM
Gary Campbell's Avatar
Gary Campbell Gary Campbell is online now
CNC Tech & Trainer
 
Join Date: Dec 2012
Location: Marquette, MI USA
Posts: 2,733
Default

Charlie...
Due to the fact that dual pumps fight each other a little the factor is around 1.9. So, 15 cfm / 1.9 = 8 (7.89) Looking at the vac for 8 cfm shows ~16.5inHg.. That should get you somewhere near real world numbers.
__________________
Gary Campbell
CNC Technology and Training
The Ultimate Woodworking Machine
GCnC411@gmail.com
https://www.youtube.com/user/Islaww1/videos

"There are 10 kinds of people in the world. Those that understand binary logic, and those who don't"
Reply With Quote
  #5  
Old 12-13-2016, 08:47 AM
rcrawford rcrawford is offline
Cobra Owner
 
Join Date: Dec 2011
Location: Alberta
Posts: 2,189
Default

Charlie, I just bought a cheap one way plumbing valve and put it between the pumps. This way I don't have to worry about opening any valves when I turn the second pump on, or forgetting to close a valve and losing a part when the second pump isn't turned on.
__________________
Russell Crawford
Cobra 408 ATC with recoil
Alberta, Canada
www.cherryleaf-rustle.com
Reply With Quote
  #6  
Old 12-13-2016, 09:57 AM
de5 de5 is offline
Cobra Owner
 
Join Date: Jan 2011
Location: Honea Path, SC
Posts: 913
Default

Thanks Gary. I can't say I understand all that, but I know enough to take your word for it. I got a good deal on this pump, so I'm gonna give it a shot. It'll also be nice having a backup just in case.

Russel, I like that idea. I was going to use valves as in the diagram below. Would the check valve simply replace one of these valves, or should it be reconfigured? Is it necessary to increase the size of the pipe where both pumps are running to the fixture? Right now I am using 3/4" pvc.
Attached Images
File Type: jpg Capture_valves.JPG (30.4 KB, 35 views)
__________________
Charlie Hind
Cobra 404 ATC with 12 tool positions & 4th Axis (2012-present)
(2006-2012 - K2 CNC... sold in 2012 to buy the Cobra)
WinCNC
www.hindocarina.com
http://facebook.com/hindocarina
Reply With Quote
  #7  
Old 12-13-2016, 10:02 AM
de5 de5 is offline
Cobra Owner
 
Join Date: Jan 2011
Location: Honea Path, SC
Posts: 913
Default

Would this type of check valve be good enough?
Attached Images
File Type: jpg Capture_check_valve.JPG (26.7 KB, 21 views)
__________________
Charlie Hind
Cobra 404 ATC with 12 tool positions & 4th Axis (2012-present)
(2006-2012 - K2 CNC... sold in 2012 to buy the Cobra)
WinCNC
www.hindocarina.com
http://facebook.com/hindocarina
Reply With Quote
  #8  
Old 12-13-2016, 10:35 AM
Gary Campbell's Avatar
Gary Campbell Gary Campbell is online now
CNC Tech & Trainer
 
Join Date: Dec 2012
Location: Marquette, MI USA
Posts: 2,733
Default

Charlie...
You can replace the ball valves with check valves in your diagram. Just switch pumps on/off as needed.

You will have to try the check valve to see if it holds up to your vac levels
__________________
Gary Campbell
CNC Technology and Training
The Ultimate Woodworking Machine
GCnC411@gmail.com
https://www.youtube.com/user/Islaww1/videos

"There are 10 kinds of people in the world. Those that understand binary logic, and those who don't"
Reply With Quote
  #9  
Old 12-13-2016, 10:52 AM
rcrawford rcrawford is offline
Cobra Owner
 
Join Date: Dec 2011
Location: Alberta
Posts: 2,189
Default

I think 3/4" pipe is plenty. You want the least resistance to airflow possible, so larger diameter is better. BUT, you also want a smaller volume to evacuate so the parts seal quicker. If you are only getting 15cfm airflow with the leakage, 3/4" pipe is probably a good size.

I use 1" PVC for mine, but I have a 60cfm pump that leaks a little more than your set-up (I often drop to 10-12"hg on some of my jigs, but my parts are larger so that still provides plenty of hold down).
__________________
Russell Crawford
Cobra 408 ATC with recoil
Alberta, Canada
www.cherryleaf-rustle.com
Reply With Quote
  #10  
Old 12-13-2016, 10:58 PM
de5 de5 is offline
Cobra Owner
 
Join Date: Jan 2011
Location: Honea Path, SC
Posts: 913
Default

Thank you Gary and Russel for your suggestions.
__________________
Charlie Hind
Cobra 404 ATC with 12 tool positions & 4th Axis (2012-present)
(2006-2012 - K2 CNC... sold in 2012 to buy the Cobra)
WinCNC
www.hindocarina.com
http://facebook.com/hindocarina
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 01:37 PM.


Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.