Time to Exhaust Air from a Known Volume of Containment

Try some of these:

Pipe Flow Calculation

Flow Through Restriction Orifice - Cheresources.com

Air Flow Conversion Calculator - ft/meter, m/s, miles/hr, ft3/min, m3 ...

I doubt if that is that simple.

You can calculate the instantaneous starting flow but the pressure comes down and so is the outflow.

So the outflow and pressure is is gradually reduced as the pressure in the container is exhausted.

Well,

Nobody here is anxious to do your job for you, even if you knew what information to provide.

Did you even bother to open any of the links?

So long.

Yes,

I did

Either measure it or make your calculations at different pressures and average it.

It's even more complicated than that: the volume of your valve's pneumatic actuator does not remain constant! As pressure is vented from the actuator, the valve stem begins to move. As the piston or diaphragm within the actuator moves, it displaces a different amount of air, thereby altering the equation.

I think this is a case where a real-life experiment would yield the best results. Try venting pressure from the same size of valve actuator through a solenoid, and if the results are unsatisfactory try a different size of solenoid. Attempting to account for all the variables here is fraught with uncertainty.

There are not any nomographs available for your application because there are too many dependant variables. Time, Volume, Pressure, Cv.

just a quick question. when you say the word exhaust...are you also using a new source of air to replace the air being moved or are we talking about going into a partial vacuum?

I am talking about reducing the air presure to atmospheric pressure without inflow of new air.

sounds like a blow-down valve or purge valve any of the manufacturers of this type of valve can tell you, just give them the piping diameter of your exhaust line. or if you have a time element they can suggest sizing. this shouldn't be hard if you're simply exhausting non hazardous air

As the pressure decreases, the flow through the valve will decrease as the square root of the decreasing pressure. Thus it is a calculus or differential equation problem, on which I am too rusty. It will behave sort of like half-life in radioactive decay.

I think that it is similar to the discharge of a capacitor equation.

You need to adapt the values. Anyone keen on this?

One wonders why time is so critical for an utility operation such as this. Perhaps the scheme needs putting in front of the local Process Engineer for review and comment before anything is designed.

The result depends on the initial pressure since flow laws are function of it. The sqrrt law is valid only within some limits.

A couple of years ago I gave indications for a similar problem in the frame of CR4: it was the time to equalize pressure between two containers. Recently a participant confirmed my results by comparison with results obtained from an other source.

It was not simple work (in fact a system of differential non linear equations with variable coefficients) but the reaction was such a lack of interest that I have not any more the equations and I do not want to do same again for nothing.

As I noticed more and more often theory is not an appreciated skill within CR4.

This fellow's scenario is even more complicated than your example of pressure equalizing between two containers. In your scenario, the containers' volumes were fixed. In this fellow's scenario, the volume of the valve's pneumatic actuator diminishes as the valve stem moves towards the zero-pressure position!

I recommend empirical testing to the OP: get a pneumatically actuated valve, try dumping its air pressure through a solenoid of known size, and then buy a differently-sized solenoid if the time is too long. It's not like solenoid valves are that expensive . . .

I am not sure to understand English very well but as far as my knowledge of this language allows me to get the point the OP mentions a FIXED volume.

I shall have a look at my spectacles may be they are not any more adapted to my view Or am I wrong and this has to be done by others ?

But even if you would be right the problem can be solved also on a theoretical way if of course one knows how to do it.

You know in general when products are designed empirical tests are done in order to verify and the actual trend is to make the so called "virtual prototyping" based on simulation with complex and more and more efficient soft packs.

You are correct that the OP says this is a fixed volume. What I'm trying to communicate is that this assumption is not true. As a pneumatic valve actuator on a spring-return control valve loses pressure, the valve mechanism will begin to move in the spring's "return" direction. This causes the actuator chamber to decrease in volume. Thus, any solution assuming a fixed chamber volume will be incorrect.

I probably misunderstood but what he meant was the time for the fixed container to empty in order to give at right moment the closing command to the valve actuator. It was not considered the whole time.

The actuator behavior was not his concern and thus neither ours.

Tornado was correct when saying: Differential equations.

Nickname was even clearer: a system of differential non linear equations with variable coefficients.

That would be the right way to calculate it. The calculations would be rigorous, and I am certainly not going to take it on.

Someone else pointed out the obvious as well - if the goal is to achieve a pressure result, contol on pressure, not time.