Originally Posted by brewfeller
I am having trouble with my March pump cavitating. It seems overly difficult to get primed. It is the center input version of the pump. it's supposed to have better throughput compared to the regular version. I have it mounted horizontally. I have seen people mount them vertically. does it make a difference? What can I do to improve the odds of priming the pump correctly without cavitation?
IMO & IME, priming these pumps is no problem at all if you have the plumbing configured properly. Obviously, the pump should be mounted at the lowest point in the system. Add a small bleeder valve on the output side of the pump between the flow control valve and the pump head. Horizontal mounting should be fine. Position the output port up if possible. To prime the pump, close the flow control valve and open the bleeder valve fully to purge any air in the pump head. The wort/water or whatever should flow easily to the pump head and flood it. Any entrapped air in the pump head or hoses should get pushed out by the incoming flow of liquid. It has to unless there is some other restriction in the circuit. I do this with the pump turned on, but you can also start with the pump off until you get some liquid coming out of the bleeder valve by gravity flow alone. When you have a very strong flow established from the bleeder valve, you can close it and open the flow control as required.
Here's some key points:
1. There must be sufficient vertical drop from the kettle outlet port to the pump intake port. More is better, but it's best to have at least an 8-12" drop and preferably a little more.
2. Use large inside diameter hose (1/2" or larger is good). Beware of restrictions caused by fittings, particularly the barb type. IOW, use large I.D. fittings and keep the elbows, etc to a minimum.
3. Use the shortest hose lengths as conveniently possible, particularly on the suction side of the pump. This is probably the the most common mistake. These pumps don't have a lot of power to spare, so minimizing resistance to flow any way you can will help a lot. Not a little; a lot.
4. Having the flow control valve closed when bleeding the system is important.
5. Make sure you have no air leaks on the suction side. This should be obvious.
If you continue to have problems, post some pics of your system and we might be able to spot something. Good luck with it.