does putting a ball valve on a return pump from sump to tank damage the pump? i have a rio 1100 in place of a mag 350 because the mag is too powerful and the overflow can not handle the flow. the return line is 4 ft from pump to tank. i would rather use the mag than the rio.
To answer your question No a valve does not damage your pump. You mentioned ball valve just to make you do not get a valve containing metal in it. Brass and copper valves are a BIG no no… you want to use pvc valve with barbed ends if you are using regular tubing and without if you are doing with all pvc.
Yep, using a ball valve to reduce the flow is about the same as adding more head/ back pressure. Still using all the electricity, but it’ll work.
Consider a T, 90*, and a ball valve. Put the T so water could go straight up to the tank or to the left 90*. Then put the 90* so it points what was going left down into the sump and put the ball valve on that. If the ball valve is closed all the water goes into the tank(too much for your return). If the ball valve is all the way open the water just circulates in your sump. Half way and your sump won’t get stagnant or be a super low flow/settling tank and some water ends up in the display.
Now if you have a power head in your sump already you can take it and put it in a 20gallon tank and you have yourself a QT tank and using no more additional electricity then you had been using. 
+1 on the tee. I have my sump hooked up this way. I have a tee, which goes straight to my display, and off the side of the tee I have a flexible tube w/ a ball valve. I use this for controlling the flow in my tank, recirculating water in my sump, and sometimes for easy waterchanges (when the substrate doesn’t need to be vacuumed).
Damage occurs when the pump isn’t supplied enough water, or is allowed to cavitate because of too much air. I don’t think that putting too much resistance on the outlet side of the pump will cause any damage to the pump. Adding a just a ball valve will not hurt the pump, but you may have pressure buildup below your ball valve, which may work loose and spray everywhere if the seal isn’t a good one.
Using a Tee for sump re-circulation is the best option IMHO. As the others have stated you will gain more control over the sump and tank flow that way, as well as reduce the risk of pump damage by deadheading the output side.
I know we don’t run low clearance high pressure pumps in this hobby, but why block the outlet of the pump and possibly damage it if you have a different solution??