Slow opening or closing of a valve

On the face of it a decision to open the valve slowly seems to be a small step to take from sudden opening yet it is almost intractable.

 

In chapter 8 I looked at valves and showed that when a valve is used to control the flow through a pipe it does so by introducing a loss at the valve. Then the relationship between the rate of flow and the valve position is much dependent on the configuration of the pipe and its supply system. There can be no independent valve characteristic that relates valve position and flow.

 

When I dealt with sudden opening I had to ignore the loss in the valve. Now it cannot be ignored because it is an important factor in determining the flow even if it is transient. So it is likely that a working engineer faced with slow opening would keep in mind graph 17-1 and design accordingly.