I originally posted this question on sci.engr.mech but this might be a more appropriate newsgroup.
FOLLOW UP POST I am omitting the response I received from sci.engr.mech as I not sure it it is considered proper to copy another's post across different newsgroups. I added the following info to my original post:
A needle valve in the bypass may be a cheap and easy way to ensure I can "tune" the system. The equipment is being installed next week after which I will have 2-3 day to get it up and running. I want to avoid any obvious problems and be prepared for those which are less likely, but still possible.
The current design calls for regulating a continuous flow thru the heat exchanger rather than starting and stopping flow. I don't expect the valve to act perfectly linearly but I want to avoid having the last 10% of valve travel controling 80+ % of the flow range thru the heat exchanger.
One of my application uses a manual 3-way valve which will be set and seldom adjusted. I am not overly concerned with the performance of that system. However I have another similar application where I seek to control process water temperature running thru the other side of the heat exchanger. In this second application the 3-way proportional valve will be actuated thru a 4-20 ma signal from a controller. Here I am concerned that the process may be unstable if the valve is forced to operate over a small fraction of its design range and at one extreme of its travel.
Comment and advice would be of great assistance and much appreciated.