I acquired four solenoid valves for use in aquarium plumbing.
12v DC, NC.
The darn things won’t open when voltage is applied with no fluid present.
What gives?
Well, I’ll start with a stupid question. Are you absolutely sure you are providing 12 volts to them? Car battery, power supply wall wart or something?
Another stupid question. Is it possible they are mis-marked and need a higher voltage?
Otherwise I guess you have four defective solenoids. I’ve never heard of solenoids that cared if fluid was present to open.
They’re probably hydraulic.
Solenoid valves can be complicated two stage affairs, and yours may rely on fluid pressure to open the main valve after a smaller bypass valve is opened. Wiki here.
A 12v 1A power supply, still putting out 13v when connect to the solenoid, the smaller rated at 40mA.
Thanks, I’ll try them with pressure on them.
Solenoids are also very sensitive to having too small of wires running to them. They pull a surge when first energized, is your power supply the recommended one for these solenoids?
It is 12v 1 A, supplies 13v when it is connected to the solenoid.
You may need more amperage for the initial surge of power they draw. It takes very little power to hold them once they open. The voltage is not the issue as much as the amperage. Also the wire size and how far you are running the wire.
What effect are you failing to get due to this “problem” ?
Its letting schrodingers cat die in the fish tank ?
Nope. But some of Schrodinger’s fish are looking a little palid.
Serious answer: I’d expect them to be internally piloted valves. That’s also the typical case for lawn sprinkler solenoid valves.
I will devise some way to get pressure on them and see how it goes.
Thanks.
The safest thing to do is to see if you get a voltage drop at the solenoid when you energise it. I would think anything more than about 2 volts would be too much. In which case you would need a larger power supply or wire or both.
Where’d you get them and what brand/model are they? That’d
a) be useful in the troubleshooting if we could look up the manufacturer’s specs
b) be hilarious in the extreme-comedy-option of “turns out they use the water for the ground path”
It is 13v when connected power supply is rated at 1A, solenoid is rated at 12v 40mA
That’s that bottom line. What valves do you have??
Pilot operated valves use very little electrical power but need significant source pressure to work; IE NOT pressures produced by a typical aquarium air or water pump. Automatic toilet flusher valves are of this design and work fine on D batteries.
Given the low operating current it sounds like an internally piloted valve. Normal home water pressure should be sufficient for testing.
Important note: While testing with water pressure it is important that you look directly down the outlet hose to make sure the valve will open 
They are moving water, Nefario.
His point was that unless the valves are designed for the application you’re using them in, they may require more water pressure to function than your water pump is putting out. e.g. lawn sprinkler solenoid valves like about 50psi and won’t work worth beans when fed by a 25 psi pump.
This might be an issue with either your test set-up or your actual application. We can’t help you answer that since we don’t have any of those details. But it is something for you to consider.
I want to stop a siphon in 3/4" PVC pipe if the power goes out.
Here are the specifications for the 1/2" solenoids:
12 VDC at 4.8 W
Pressure: 0.02 - 0.8 MPa
Sea level air pressure is 101,325 Pa so we aren’t talking about very much here.
Is that the pressure it must have on it to open?