I tried three different needle valves to try to regulate the flow on my water injection. All drifted from what I set them at. On a hunch I tried one of the drip thingies (emitter) that have a diaphragm type flow regulator intended for lawn irrigation. Works great!
I only had 1 GPH drippers, and wanted to slow it down a little. I bought a bag of 25 emitters rated at 1/2 GPH. I thought maybe I should start the engine then plug them in. Then thought "Naw, it will be ok.". Every one of them is defective (made by Raindrip). No diaphragms. The engine sucked in about a pint of water before I could shut it off. Does not seem to have done any damage, but very scary nonetheless.
I now using a 1 GPH emitter that seems slower than the rest. One GPH may seem like a lot, but remember they are intended to run at 25-30 PSI. I used about 3 ounces of water in 18 miles. A little more than I would like, but I think I am on the right track. I probably will make a set of calibrated emiiters eventually.
"Diaphragm" emitters all use some type of flexible diaphragm to reduce the flow and pressure. There are many ways used to do this. The bottom line is they all use some type of flexible part that moves to restrict the water flow. As with anything that moves, they will wear out eventually (which may be a very long time!) which is the downside. The advantage is that they tend to be much more accurate in controlling the flow and pressure than the previous types.
I am using this type emitter, also called a dripper depending on the manufacturer. So far it has worked far better than the needle valves I have tried.
They are calibrated to regulate flow, and I have one installed between the water supply and the carburetor. The bubble line for air coming into the jar gives me an indication of how much water is being consumed.
There are two main types of air pressure regulator: bleed type, and non-bleed. It is doubtful that either will work to control water flow.
I've started toying with the idea of water injection to cool down the lean hot burn. My plugs are really white. No predet yet. First attempt was to use venturi vacuum. Nope, a multi port injection throttle opening is too large to have enough velocity to pull water through a tube.
Then I tried manifold vacuum and a carb jet. Too much at idle and made it rough. So I'm going to use a micro switch and a vacuum solenoid to only switch on the metered water at some throttle position above idle.
If this proves to be any help, then I'll consider building something more advanced. A pressurized injector that has an injection pulse width based on throttle position shouldn't be too difficult to rig up.
Oh if my MPG goes down from the last entry (36.7) that will be because I fixed the AC today.
I found a problem with the irrigation drippers I should have foreseen. Adding alcohol doubles (maybe more than that) the flow rate. Still have not tried the 1/2 GPH drippers. The first batch I bought was defective.
I'm following this thread and your idea. Not sure if it matters but I was wondering if having a constant vacuum applied to the emitters is the problem.
Anyway, what about a water injector solenoid that is wired to one of the injectors to use the duty cycle of an injector pulse? Or maybe using parts from a timing light and use the pulse from a spark plug wire for injection signal?