Valve(s) for switching between vacuum and compressed air

[AligatorAmy]

Hi,
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

https://www.amazon.co.uk/shut-valve-pneumatic-vacuum-push/dp/B00B7ZSH1G

.
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
Regards

 

[jari001]

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

 

[mk3223]

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.

 

[AligatorAmy]

@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.

 

[hydtools]

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?

Ted

 

[moltenmetal]

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.

 

[mk3223]

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.