Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.


Valve(s) for switching between vacuum and compressed air

Valve(s) for switching between vacuum and compressed air

I do some rapid prototyping using simple pneumatic system. Please refer to the attached draft.
As outlined on the draft, the air in the container is slowly pumped out (with vacuum pump, there is only little bit of air pumped out), with valve 1 opened and valve 2 closed, and then the air is slowly 'pumped in' back to the container with compressed air, by closing valve 1 and opening valve 2, making the air inside the container slightly compressed.

Because vacuum and compressed air are 'gentle', i.e. there is no great vacuum or highly compressed air, initially valves 1 and 2 outlined on the draft, were regular one way valves, like this one .
Despite low vacuum or pressure applied, closed valve 1 by opened valve 2 was 'leaking' and similarly closed valve 2 was 'leaking' when valve 1 was opened.
My questions is: I am not sure what kind of valves should I use for this scenario. I am looking for rather non-expensive valves as this is low cost rapid prototyping stage.
Please help

RE: Valve(s) for switching between vacuum and compressed air

Maybe you got bad valves/broke during install? Maybe the valves you are using can't tolerate the dP?

RE: Valve(s) for switching between vacuum and compressed air

IMO, it's possible that the leak from the tubing connections in the system or through the valve seat. Perform a leak test to make sure the connections are properly tightened for the tubes and valves. A ball valve with a soft seat material should be proper for the compressed air system.

RE: Valve(s) for switching between vacuum and compressed air

@jari001, mk3223,
Thank you for your replies.
The valves have been tested separately and seem to be in order, likewise the connections with tubing, etc.
It seems to me that when e.g. valve 1 (outlined in attached draft) is opened and valve 2 is closed, then valve 2 as one way flow valve is enforced to pass the flow in opposite direction than is meant to due to the vacuum created by the pump. In order to fix that I considered application of two ball valves, one to the right of valve 1 and one to the right of valve 2. But certainly there might be a better way to fix the problem.

RE: Valve(s) for switching between vacuum and compressed air

Are the valves directional, meant to flow air in only one direction? If so, are they installed backwards?

How do you know that the valves are, in fact, leaking when closed?

Is it possible that the container is leaking?


RE: Valve(s) for switching between vacuum and compressed air

No time for a detailed analysis, but here's something to consider: if the valves in question are solenoid valves, unless they are "direct acting", then they need differential pressure in order to operate their pilot. These valves are not useful in situations where you're switching in services where there is no differential pressure- they will either not open or not seal when closed.

RE: Valve(s) for switching between vacuum and compressed air

Sorry not too much help to your system.
But, did the system do the leak tests in both pressure and vacuum conditions for the "one way" valve? Or, to use a bi-directional on-off valve to simplify your solution.

Good luck.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close