Question
I am working on a lake fed system that was working fine we cleaned out the vuflow shut it down went to get parts and thats when we noticed we had lost the prime. This is a homeowner built system and we  do not see a ball valve or a check valve anywhere in the system. Should there be one and if so where would it be. Also how do we reprime the system.

Answer
I would suspect that at the origin of the supply line (in the lake)there is a "foot valve" or some such other one-way valve that is malfuntioning and keeping the line from priming.  YOu will need to get to it some how to see if it is working.  They need to be replaced every so often.  Once it is determined to be fixed, you should be able to prime the line by pouring water into some opening either in the pump itself or in a device that is attached to it for the purpose of priming.  You may have to unscrew a fitting on the line to pour water into it.