OK, that aside was relative to the comment about a car on a small battery.
To indicate at what sort of distance from the valve being operated?? A small flagon a pivot with two solenoids to move it, and diodes in series with each so that only one can be powered from each polarity.
OR, if the water flowing out of the valve is at any pressure head, even a few PSI, a vertical (water) hydraulic cylinder to raise a flag to show discharge pressure. It would take a very low friction cylinder, or maybe a diaphram cylinder, not a standard one.

 

Please keep on topic.

Definitely. Was just defending my observation about farms with 9V batteries for irrigation. I'd still like to know exactly what we're being asked to work with. Seems the TS isn't quite as interested in his thread as the rest of us are.

 

I think the answer is "He WANTS remote monitoring". Or to be more precise:

NEED? No. "Find it HANDY"? I get it. He wants to know what state the valve is in when he (probably) applies water pressure to the solenoid.

This doesn't sound like any farm I'm familiar with. But then again, I'm not a farmer, son of a farmer, related to a farmer, know a farmer or anything else related to farming other than those systems where they have a well sunk in the middle of a field with a pump and one of those circular watering rigs. Farms - as I can imagine - would have some major source of power for pumping water. A solenoid valve like what's on my Drip Irrigation garden that is powered by a battery has the type of solenoid valve that uses a pulse to open and a pulse to close. One year I had old batteries in one of those timers. Barely enough power to open the valve but then just not enough power left to shut the water off. I had to go out there and manually shut the water off.

OK, so you want to know the state of the valve at the last pulse. It's not likely there's any kind of lever or manual valve on the solenoid to get a sense of what the position is in. So your idea of a "Last Pulse" circuit that doesn't continuously require power makes sense to me. Those magnetic indicators I posted in posts # 7, 8 & 9 seem attractive to me. IF the solenoid valves are like what I think then this is the only way I can see having a chance to work at all. But there's always the possibility of a pulse failing to be read by the indicator, possibly leading to a false indication. Since you would find it "Handy" then it's not necessary for any real conditions you may encounter. Your last reply:

seems to indicate battery operated; which makes sense that you don't want a continuous draw of power. It also suggests to me your definition of "Farm" is not the same as I would define. But that's OK. You can call it whatever you want. I just see it as one of those drip irrigation systems that run on a 9V transistor battery. I think, and this is purely my personal opinion, you're going to have more trouble wiring in any kind of indicator, regardless of the consideration for continuous power drain or not. I still have a few battery powered drip irrigation systems somewhere in a drawer along with other drip plumbing equipment. Currently, my wife's gardens are all run from a 24VAC sprinkler control valve. The valve is only open as long as there is power applied to it. Remove power and it's off.

So I leave you with a question: Is this "Farm" nothing more than a garden with a drip irrigation system that is battery powered?

To answer your question about the farm... I have over 200 acres of fruit and vegetables, a 3-phase pump that does 200gpm with about 3 miles of pipe and wire that was buried with the pipe 40 years ago. Stuff decays with age, and the same is true of wire so it is now difficult to control the remote valves (and we're talking about 500 m runs on average). The valves originally worked the way your home system does with 24v a/c. Also, the preferred location of the valves has changed over 40 years so pipe extensions leave me without a way to control the valve remotely. All the irrigation is trickle (buried). My academic background is systems engineering, so I'm comfortable tinkering in the basement.

Thanks for your lead on the flip dots. I contacted the company and they come out to be like $10 each if I get a half-dozen. I'm going to wait until everything else in the circuit is working and then decide if its worth it.

 

Maybe a mechanical valve position indicator fitted to the valve?

A good idea except that the valve is buried inside a case which is buried in the ground in order to avoid freeze damage. Sorry I wasn't more explicit in what the valve looks like. Here's a link to a good example

 

If a zero-power-consumption VISIBLE indicator is what you want, a mechanical flag indicator driven by a solenoid,magnet linkage could work. The solenoid, in parallel with the valve, would push one way or the other to indicate which polarity was last applied. Sort of like a railroad "flag semaphore" arrangement. If an electrical signal were required, magneticly held polar relays have been around for many years. one of those would serve very well.

This is a good idea. Basically a "shadow" solenoid that mimics what is going on down in the valve. Only downside is that the solenoids I've seen don't have much throw to them. But I haven't looked very long either. It's a good idea.