Closed loop physics question?

[mxracer19]

Since a closed loop is just what it sounds...a "closed" loop; If (1)the supply and return bulkheads are at the same level, and (2)the length of piping to and from the pump is the same, and (3)the pipe diameters of the supply and return are the same, then theoretically, wouldn't the head pressure caused by the siphon of the supply to the pump balance with the head pressure caused by the height of the return, given a pump that is X feet under the tank?

Thanks,
Matt

[quader94]

ask in the general hopefully youll get answers there

[Jnicho]

I believe you are correct...the "head" balances out so to speak.

[crvz]

So I think what you're asking is if you can negate head loss due to vertical height since you have water flowing in both directions, right?

The short answer is no. When the pump is off, obviously everything is in balance and water won't be moving within the closed loop plumbing. If you're comparing the same pump placed at 1 ft below the tank vs. 10 ft below the tank, the first scenario will have much higher flow rate. The pump is still doing all the work, and it takes a lot more effort to push water 10 feet up than just 1 foot up, and this negative pressure on the return flow is not eliminated by the positive pressure of the supply line (think about it; is it easier to go up stairs or down stairs?).

[Dagrape]

Originally Posted by crvz

So I think what you're asking is if you can negate head loss due to vertical height since you have water flowing in both directions, right?

The short answer is no. When the pump is off, obviously everything is in balance and water won't be moving within the closed loop plumbing. If you're comparing the same pump placed at 1 ft below the tank vs. 10 ft below the tank, the first scenario will have much higher flow rate. The pump is still doing all the work, and it takes a lot more effort to push water 10 feet up than just 1 foot up, and this negative pressure on the return flow is not eliminated by the positive pressure of the supply line (think about it; is it easier to go up stairs or down stairs?).

The only Head on a closed loop is from friction loss in the piping. the head pressure on the suction side does in-fact counteract the head on the discharge side.
You can prove this by taking a extremely cheap low flow low pressure pump and put it in the basement and plug it in. You will notice if both suction and discharge are below the water line in a true closed loop fashion, the pump will move the water. Then move the suction line to the basement and watch how the pump will be overcome by the discharge head pressure, and watch yoyur tank empty into the basement.