Gary, I am not sure how your return lines are set, but if you have 1 return pump for 2 return lines till the tank, i do not see why there should not be a valve in the return line.Well, I was scrolling through Facebook today and saw a picture of my sump on the R2R page. It linked back to a thread entitled - Fix My Return Pump Problem. Not really sure why they used my sump as an example, except that there are two Vectra M-1s visible in the picture. Anyway, glad they did, because it saved me from redoing some plumbing. (See my last post above).
So anyway, I went to the thread and it involved a problem with an Vectra return pump, or plumbing. During the conversation it was noted that you shouldn't use a valve on the return line with the Vectra, use the controller to adjust the speed of the pump. This is something that I know, but because this build is taking so long, I totally didn't think about that while I was trying to plumb the return into the SeaSwirls to include a gate valve. So, back to the drawing board there. Glad I didn't permanently glue it up. Almost another mistake. ;Wideyed
You will only have to make sure that you do not close both more then 50% at the same time. This to have the outlets not smaller then the pipe diameter at the pump so you can ensure free flow in the line at all times.