spring rate and vacuum

[Guest]

How do I convert vacuum to spring rate? What I am trying to find out is how stiff a spring is needed to overcome a certain amount of vacuum. This is for a type of check valve and the vacuum is the human mouth creating suction.

[G]

Anyone? I may not have been clear in my question. Springs are sold with a specification of the rate of pounds per inch, as in how many pounds does it take to compress the spring 1 inch. Vacuum is rated in inches of mercury or H2O, and this can be converted into pounds per square in. How can I convert pounds/in sq. to the pounds per inch rate of a spring?

Thanks to anyone that can clarify this for me.

[Guest]

On the diaphragm, you forgot to multiply by the area. The actual force (when just beginning to open) is 2.43 lb.

The x is the preload of the spring, which you didn't give.

Once the valve begins to open, you have a very complex flow situation, and you will have to look at dynamic pressure in the flow (Bernoulli's equation). Since I'm an electrical engineer, that's beyond what I can do with a flow problem. I don't know how to calculate the fully open situation.

[G]

Thanks for the reply.

So the initial cracking pressure is directly proportional to the amount of preload, but after that it gets more complex.

I'll have to research Bernoulli's equation and do some more trial and error testing.

Thanks-