Just about every system needs a dump valve.
The dump valve is a necessary part of misting. It basically keeps your nozzles from dripping. It does this through a solenoid valve placed in the high pressure line.
You put a tee in your high pressure line and then install a solenoid valve.
Sounds easy so far, but wait, you have to operate it.
Solenoid valve basic operation.
Ideally your dump valve should be a normally open solenoid valve.
It should have a pressure rating higher than the pressure you are operating at.
When you turn on you pump you want your dump valve to closed, right? If the valve is open all water will pump to drain, not to your nozzles.
When your pump starts, pressure is built up. That water pressure is delivered to your nozzles.
Your problem is, when the pump shuts down the pressure decrease slowly through the nozzles. During this time frame nozzle performance is poor, they spits, sputter, and stream water. Thing get wet.
The idea of a solenoid valve dump is to relieve the system pressure quickly by dumping water to the drain. The high pressure nozzle piping goes to zero psi quickly.
What happens, your nozzle don't spit, sputter, or stream. Hay let's call it SSS.
Sound easy to do, well not quite.
There are a couple issues that have to be analyzed.
One, how do we control this solenoid valve? Two, when we dump (drain) we don't want to end up draining the whole system, not good. Let's see what we can do about this.
Dump (Solenoid) Valve Control
We are not going deep into solenoid control. I would end up talking to much about other control. Let's not muddy the water. Basic content at this point.
Above I said you need a normally open dump valve. It's not necessary but makes life (control) allot easier.
When you turn on the pump, you turn on the valve (it closes). Then the reverse is true, the valve dumps. Easy enough.
But what if you don't have a normally open solenoid. They are hard to find and doubly hard to find rated at high pressures. You have a normally closed solenoid valve. Well, then you need a relay to operate the solenoid. The relay will - control - the solenoid for proper on/off operation. Solenoid power off when pump power on. Then, solenoid power on (dump) and pump power off.
That's complicated enough at this point.
Once you get to this point you can see you're not just plugging your pump into the wall or flipping a switch any more. You are looking at control boxes, extra wiring, and thinking - what else do I need.
Dump valve drain piping.
When you dump, the point is to relieve pressure. So it could also be called a pressure relief valve because that's what it does. But the term pressure relief valve is already being used on a different product. So dump valve it is.
But we can't just dump. We have to consider what's happening. What could happen? Yes, the pressure is reduced to zero, great. And if we have spring check valves in our nozzles, they will close. No SSS, that's good. Things are working
But what if one of our nozzles does not have a check valve? Or one of the check valves is not holding well. Our system will drain.
If our dump solenoid is near the pump (low point) and the nozzles line are up 12 plus feet in the air (high point) the lines will drain.
Nothing disastrous is happening, but when you start the pump back up you will not get mist right away and you will also get more SSS. Why, there is alot of air in the line, it is slower to build up pressure and eliminate that air. It’s like you were starting up your system for the first time.
So, what do we do? Well, we have to keep the lines full of water. When the lines are full the mist appears quickly when you turn on the pump.
There are two things to do. The first is to shut the solenoid back off, closed, and hold the water in. The second is to create an inverted trap to trap the water up high and keep it from syphoning.
Here is a little video to help explain it.
This first video is a time delay dump. 2 sec. dump
This second video explains an inverted trap concept.