You need to know the minimum voltage the coil requires and its current load to calculate the voltage drop over that distance for your specific solenoid valve.
On-line voltage drop calculator here (scroll down):
You have a better chance using a 120VAC solenoid working at that distance, given both solenoids have the same power requirements. The inhibiting parameter will be voltage drop. The 120VAC solenoid only requires 1/5th the current of a 24VDC version. and voltage drop is proportional to current. Even using the 120VAC model, you should calculate the voltage drop for the wire size you plan on using.
> need to activate solenoid 2500' away. would a 24vdc solenoid work or would i need a 120vac solenoid?
Voltage drop is your concern. To feed a 120v ac coil (ampacity roughly 0.1-0.3A) from 2500' would require a conductor about 1/2 the diameter of a man's wrist.
What have you for power at the solenoid's location? Is there any existing cabling between the two points? Would sending a wireless signal work? More detail would help.
I think you dropped a zero or something there. You certainly don't need a wrist-sized conductor to drive a single solenoid at 2500'. I'd certainly choose 120V over 24V at that distance, and I might run #14 AWG conductors, but wrist sized? No way.
You could also compensate by having a little higher voltage, say 125V, at the supply end, or sending 230V and transforming to 120V at the far end, or even just buy a 230V solenoid. Or, just find a 120V solenoid with good tolerance for slightly low voltage.
> need to activate solenoid 2500' away. would a 24vdc solenoid work or would i need a 120vac solenoid?
It's too far to operate a 24 VDC solenoid directly. 120 VAC should work
Alternately if you want to use a 24 VDC output and you have a source of power at the solenoid location use a 24 VDC relay then you can use whatever Voltage is available to provide the operating power.
If it's all indoors and on the same electrical system, I'd maybe run the wire. If it's outdoors, you can afford to look at alternatives for the cost of the wire and protecting it somehow from the weather. Depending on exact situation, the best way could vary, If there's power at the other end you could do some sort of signaling, even a radio link might be attractive, if the reliability is good enough. it's a lot of doing to do it right for half a mile. But if you have to run one lone solenoid way off by itself, wire might be the only way. Half a mile of 12/2 UF would be pretty spendy. Plus the trenching.
