How Relays work

[newsalt]

I'm wanting to build an Automatic Water Change System. I'm hoping someone can explain how a relay works. What I want to happen in the system is be able to push one button and and have various pumps and solenoid valves turn on and off. I'm pretty sure that relays would be involved in doing such a thing, but I'm not sure how to wire these things. If someone can explain a simple relay loop like turning a pump on, I could probably figure out the rest.

Thanks

[schwintosky]

A relay works by 'relaying' one signal into another. For something like a push button and an ice cube relay, when you push the button, it powers up a coil that creates a magnetic field and pulls a very close but not touching metal contact into place where a close circuit is created between whatever device you want to turn on.

So when you push the button, it creates a closed circuit for the device you want to power and that device is turned on.

[xtm]

http://www.the12volt.com/relays/relays.asp

That is an automotive type Bosch relay, but the principle is pretty much the same. Look at the schematic- http://www.the12volt.com/getimage/relaytext2.gif
Basically when you energize the coil (terminals 85 and 86) you create a contact between terminals 30, 87, and 87a which completes a circuit. Relays are used to separate one circuit from another circuit, or to control a larger voltage using a small voltage (or vice versa)

Hope that wasn't confusing..

EDIT- I don't know what kind of relay you're going to use, but you need to make sure that you place a Diode across the coil terminals to 'stop' Back EMF caused by discharging the coil. This spike can damage the relay itself or other equipment. Some relays have this diode built-in.