Tim, they can be shut off totally if you are spraying. The need a little movement through the pump. You can shut them off for a few minutes without spraying but an extended period of being shut off totally with the pump still running would start to build up some heat which would likely affect the microbes. Running that way for an extended period will take the seal out of the pump. You can run the agitators so it is just sort of trickling out of the agitation and not have any adverse effects and I am sure it would not affect the tea. A pump that ran only when you needed it would not be that hard in a unit that was pulled on or mounted on some kind of vehicle such as the Walker that was mentioned but would probably be a bit of a trick in a rig where you were applying the tea with a gun such as a 100 or 200 gallon tank sprayer. The pump in the photo looks like a surflow which is a decent pump. There are better choices. I believe I mentioned earlier in this thread that I know more about sprayers than Tea but am doing the best I can to learn more. You brew tea by aerating it but big bubbles are bad and little bubbles are good as I understand it. I almost have a feeling if you took the three best experts in the world and put them together that there would be some areas where their ideas were very different. It is really an interesting subject and there does seem to be a lot of conflicting information. Lawnsite and you guys are really a good resource for learning.