Maintaining Vacuum on CNC Equipment

      Considering pipe sizes, pump setup, and a vacuum reservoir tank. June 30, 2005

Question
When installing a 20 hp vacuum pump to a 4 x 8 CNC, should the PVC pipe from the pump, which is 4", be reduced to a smaller pipe?

Forum Responses
(CNC Forum)
From contributor D:
As far as flow is concerned, you would probably be okay with 3 inch pipe. I doubt that the ports on your machine are any larger than that. The 3" pipe and butterfly valve are probably a little cheaper.

One advantage to the larger pipe is that it provides a vacuum reservoir when snapping down warped panels. When you crack the valve at the machine, you get a brief inrush beyond the capacity of the pump. The larger the volume of the pipe, the bigger the reservoir. I have even seen installations where a length of very large diameter pipe (12"+) is used as a "tank" just behind the machine.



From the original questioner:
The system I am using has a 4" outlet. It is connected to a 3" manifold with 4 valves. It is then reduced to a 2" web of pipe to run a 4 zone table. The vacuum holds the parts okay, but it will not snap down the 4x8 plywood like you described. Also, where the 3" connects to the 2", the sweeps on the T's are not with the flow from the pump. Would this reduce vacuum?


From contributor D:
As I understand it, your router has a 3" pipe off of which come four 2" pipes. The four pipes run to four zones and are individually valved. In order to get your part to snap down with a 20hp pump, you will need a reservoir as described in my previous post. You will also need all of the four valves to open at the same time. I really don't think that the sweeps being backward on the tees is a big issue, but if you are replumbing, I would certainly turn them around.


From the original questioner:
Yes, you understand right. After looking at it closer, there does not seem to be enough room to replace 2" with 3", but I could build a reservoir. I assume I could place 1 3" valve in front of the 4 2" valves to switch on at once. Once the vacuum snapes the plywood down, does it stand a better chance of holding it?


From contributor D:
Once the part is pulled down, the system will reach equilibrium and the reservoir will have no effect on the end vacuum. The only way to maintain deep vacuum with bleed boards or other leaky fixturing systems is by application of sufficient horsepower. In your case, a 20hp screw, vane, or liquid ring pump is more than enough for a gasketed fixturing system, will work well with a bleed board for medium to large parts, but may be a little weak for nests of small parts on a bleed board.

Would you like to add information to this article?
Interested in writing or submitting an article?
Have a question about this article?


Have you reviewed the related Knowledge Base areas below?
  • KnowledgeBase: Knowledge Base

  • KnowledgeBase: Computerization

  • KnowledgeBase: Computerization: CNC Machinery and Techniques


    Would you like to add information to this article? ... Click Here

    If you have a question regarding a Knowledge Base article, your best chance at uncovering an answer is to search the entire Knowledge Base for related articles or to post your question at the appropriate WOODWEB Forum. Before posting your message, be sure to
    review our Forum Guidelines.

    Questions entered in the Knowledge Base Article comment form will not generate responses! A list of WOODWEB Forums can be found at WOODWEB's Site Map.

    When you post your question at the Forum, be sure to include references to the Knowledge Base article that inspired your question. The more information you provide with your question, the better your chances are of receiving responses.

    Return to beginning of article.



    Refer a Friend || Read This Important Information || Site Map || Privacy Policy || Site User Agreement

    Letters, questions or comments? E-Mail us and let us know what you think. Be sure to review our Frequently Asked Questions page.

    Contact us to discuss advertising or to report problems with this site.

    To report a problem, send an e-mail to our Webmaster

    Copyright © 1996-2019 - WOODWEB ® Inc.
    All rights reserved. No part of this publication may be reproduced in any manner without permission of the Editor.
    Review WOODWEB's Copyright Policy.

    The editors, writers, and staff at WOODWEB try to promote safe practices. What is safe for one woodworker under certain conditions may not be safe for others in different circumstances. Readers should undertake the use of materials and methods discussed at WOODWEB after considerate evaluation, and at their own risk.

    WOODWEB, Inc.
    335 Bedell Road
    Montrose, PA 18801

    Contact WOODWEB











  • WOODWEB - the leading resource for professional woodworkers


      Home » Knowledge Base » Knowledge Base Article