Float Fill Valve
installed a rainbird solenoid valve to fill an underwater tank with a float valve. what type of relay to use?

I installed an automated rainbird irrigation system and installed a 1" poly pipe line from the basement to fill the exterior water tank. I also installed a float valve in the tank and was wondering what type of relay switch is required to install that will turn on a rainbird solenoid valve to fill until the tank is full... I have power at the tank and know that i will need to convert 120v to low voltage. any ideas... thanks

If I understand this properly, if you have a float valve (one that shuts off when the float is raised, like the cistern in the toilet) surely that does the job on its own? It should be in the top of the tank. No need for a solenoid valve.

A solenoid valve would be operated by a water level sensor or a float switch. Similarly, the float switch is in the top of the tank, and it opens the valve when the level drops, closes it when the float comes up. You can reverse the action using a relay (if the switch or the valve are the wrong way round). However, the solenoid valve should be closed with no power, if you don't want the tank to overflow for a power failure. Similarly the relay should operate when the tank level drops, so that the solenoid valve opens then. The float switch contact closes when the float drops. The relay contacts close when it is operated, and the valve opens when it is powered.

The float switch will have hysteresis. That means when the level drops enough to operate the switch, the level has to increase past that point before it switches off. This stops the valve cycling with small changes in level.

The other purpose of the relay is to relay the switch contact on the float. The float switches 12 or 24V AC or DC to suit the relay coil. The solenoid valve is switched by the relay contacts. It could be the same voltage supply if that suits the solenoid valve, but a higher current than the contact rating of the float switch.

Alternately the solenoid valve could be a 120V one (if the relay is 120V rated and the solenoid valve is designed for the environment). The solenoid body should be connected to the supply ground by a separate wire, so it has three wires. I would also connect any metal parts of the water tank together and to ground.

The relay has two ratings. The relay coil is according to the supply you use, so probably 12V DC, 24V AC etc. That in turn should be within the rating of the float switch contacts. I would use 24V AC if there is a choice. The relay contacts should be rated to switch the voltage and current of the solenoid valve.

The power supply you use needs to be rated to supply the voltage and current required by the relay coil. If the solenoid valve uses the same voltage (e.g. 24V AC) the power supply is rated to provide the current for the relay coil plus the solenoid valve. The body/case/frame of the power supply should be grounded to the AC supply ground by a separate wire or through the wall outlet ground. If you need 24V AC the power supply is just a 120V to 24V transformer in a box, e.g. 24V x 4A = 100W. The power supply should have its own fuse, mounted out of sunlight and weather.

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