Quote Originally Posted by mad fridgie View Post
TEV will be open not closed.
As I've read, it will be closed on system start, until sufficient SH has been reached, after which it will open.

A cap has its place, and indeed can equal a valve at a fixed point, "Optimum", but there are very few systems where all process variables are constant, thus keeping the system at optimum.
Now, this is something the industry seems to have fixed in our heads regarding a cap tube. Is this actually true, though?

In other words, what process variables, or grouping of variables, needs to remain fixed, in order for a cap tube to work over a wider operating range? If both Te & Pc slide together, is there a group that remains relativley constant? Perhaps it is time we re-think a little more about cap tubes?

Practically a valve does allow for inperfection in design, as a cap needs to be right. For one off applications, the time spent optimising the cap, (cost) will be greater than the value of the valve installation.
I agree that present software is an aid to cap selection, no a fixed solution.
Does the cap tube actually need to be 'perfect'? Perfect at what point in a system? Could a target point in the system be selected & used for nominal cap tube sizing? Does it really need all the laborious cut-&-try efforts we hear about in the received logic?