# Head in a closed loop system?



## predator (Jan 28, 2005)

Ok so... I should know this seeing that i have the whole engineering back ground and what not, but here goes...

Ok in a closed loop sytem such as a canister filter do you even have to worry about head on the pump?

I get that if you have an open sump there is pressure pushing back against your pump as it forces water up the tward tank hose...

BUT in a closed system... ther is pressure pushing down with the same force from both the pump inlet and outlet... These pressures should equalize things out therefore (virtually) eliminating head... TRUE?

Im asking this because i was trying to look at somethign and someone had an 8 foot head and he put 2 canisters in series with each other to defeat the head... but it was a closed system so i was kinda thinking "what head?"....

I do realize that ther will be more pressure on the pump outlet side of the system due to elbows, heaters, uv filters, spray bars, and what ever else you run it through...

-me


----------



## Damon (Jan 18, 2005)

In theory yes...........
Let me see if I get this right.
In a perfect vacuum, that would hold true. But we know that is not always the case. Air bubbles and debris in the waterflow created by numerous things will have an effect. I would guess it would be insignificant but would cause some head. Also as your filter pads clog. the flow would decrease on the return end. 
The canister can handle only so much flow. Could lead to overflow if not balanced.

Just my first thoughts on the matter. Feel free to correct me.

Found this link...... Probably more accurate... 
http://fish.suite101.com/article.cfm/choosing_a_return_pump


----------



## TheOldSalt (Jan 28, 2005)

As long as you don't get any air bubbles in it or clogging, you can pretty much forget about head pressure. That's the beauty of canister filters. The way people tend to get into trouble with this is by rigging things up in such a weird way as to make the output hose longer or steeper than the intake hose, or by putting too much resistance on the outpot hose in the form of accessories.


----------

