???ehiem variable speeds 120v rheostat ???
 

If I wanted to make a ehiem variable speeds could I just stick a 120v rheostat in line, or would that burn my house down and kill all the little children? Or how could I make it work like those magic hydrothunder things?

I don't know the specific of that pump, but in general AC powered pumps use synchronous motors - meaning it rotates at a set multiple of the power line's freqency. To change the speed you would need to change input frequency, not the input voltage.

May I ask, why? I doubt slowing it would make it any quieter, and I don't really like the idea of overpowering a pump...

Heh - over clock your water cooling system cooling your over clocked PC :P

I want to test cooling at slower water speeds just for fun.

I've attached a 220v pump to a halogeen spot trimmer, making it go from 160 to 230v.
It only started to run at 190, same noise level (even higher) , less head and my trimmer got damm hot!

To spped it up or slow it down you need to change the freqency, and those things are quite expensive. Only changing the voltage will give it less power, making it stop spinning sooner.

If you want variable, why not go for 12v pumps?

Are you saying with a 12v pump could I just change the voltage? What 12v pump brands are good?

put a valve in your system then.

Wouldnt the valve just cause more pressure causing the water flow to speed up?

More back pressure reduces flow. You'll see an increase in velocity through the value, but the flow through your block/radiator will be reduced.

You can do what I have done before which is hook up a fan dimmer inline with the pump. Power decreases but the speed sounds about the same. If you go too low the pump will just stop and chatter. I never did test the flow since I was just messing around so I don't know how effective it is as a flow regulator.

Read this for a detailed explination:

http://episteme.arstechnica.com/eve/...m=987000222631

(Particularly JimZ's link which explains everything from fan motors to dimmer switches)