CL pump, better on floor or up high?

[Anonymous]

My Iwaki 40 sits on the floor, four feet below the bottom of the tank.

I wouldn't get any extra power or increased efficiency if it was up at tank-level, would I?

(Note: this is a Closed Loop pump. It is fed from 2 1.5" bulkheads on bottom of the rear pane.)

Thanks

 

[Anonymous]

You would get an increse in flow if you shortened the pipe. It would probably not be enough to notice. The friction losses in the pipe are per lenght. Here is a reference chart for flow losses. Notice they are ft of losses per 100 ft of pipe.

http://www.plumbingsupply.com/flowchart.html

 

[Anonymous]

Thanks Wazzel,

I think if I put my pump up high, then I'd need to add at least one 90-degree pvc angle. That would take away any amount of gain from shortening the pipe.

The reason I asked is that I saw on another board, a noted expert suggested placing CL pumps up high, so as not to lose flow from 'increased head pressure.' That sounded wrong to me as head pressure on a CL is just the distance between the bulkhead that feeds the pump and the height of. the return.

 

[Anonymous]

>...a noted expert

He/she has too much head pressure....

To be fair, I need to read the thread to see if there is some merit in the statement. PM me with the link and I will see if I want to retract the line above.

 

[Anonymous]

>...a noted expert

He/she has too much head pressure....

LoL, I tink he was just misinformed at time of posting. :lol:

 

[Anonymous]

Seven, PM sent.

 

[trido]

I disagree guys. My understanding of head pressure is that the water pressure in the pipe causes resistance. The more water pressure the more resistance. For instance. The mag 18 Chart from marine depot labeled "Flow Rate Vs Pumping Height". At 2'-1630, @ 6'-1125. 400GPH loss.
The Sequence Barracuda: @2'-4250, @6"-3250. 1000GPH loss. I would guess the manufactures test with only a straight pipe of different vertical heights to get these numbers. We, also have to take pipe friction into account. From what I have read, The Sequence pump also shows a wattage curve showing that head pressure does effect efficiency. I may be wrong, but I am trying to think of ways to keep my CL pumps as high off the floor as possible.

 

[Anonymous]

IIRC, for a CL pump placed on the floor, head pressure isn't measured from the floor up to the returns.

Imagine turning off the CL pump. Water in the return pipe would naturally rise to the level of the tank. The pump doesn't need to push the water all the way back up to the tank, so actual head pressure is very small.

This is much different from a Return Pump. A return pump, from a floor-level sump, actually does have to push the water up to the height of the tank. So head pressure is calculated, as you stated, for those.

But as Wazzel pointed out, flow is still lost due to resistance from the longer piece of tubing, even if it's straight.

 

[Anonymous]

Thanx for the link. Yeah, he was confused on that thread. The placement of a close loop pump is not important since there is no hydrostatic pressure (just ensure both input and output are submerged at all time). As Waz said, it is best to shorten the total pipe length due to hydrodynamic "head pressure" due to friction between the moving water and the wall of the pipe.

 

[trido]

Imagine turning off the CL pump. Water in the return pipe would naturally rise to the level of the tank. The pump doesn't need to push the water all the way back up to the tank, so actual head pressure is very small.

This is much different from a Return Pump. A return pump, from a floor-level sump, actually does have to push the water up to the height of the tank. So head pressure is calculated, as you stated, for those.

quote]


I now understand the difference between a return pump and a CL pump.

 

[Anonymous]

>...I now understand the difference between a return pump and a CL pump.

Oh, even perfect people like me make mistakes too... :wink:

 

[Anonymous]

I disagree guys. My understanding of head pressure is that the water pressure in the pipe causes resistance. The more water pressure the more resistance. For instance. The mag 18 Chart from marine depot labeled "Flow Rate Vs Pumping Height". At 2'-1630, @ 6'-1125. 400GPH loss.
The Sequence Barracuda: @2'-4250, @6"-3250. 1000GPH loss. I would guess the manufactures test with only a straight pipe of different vertical heights to get these numbers. We, also have to take pipe friction into account. From what I have read, The Sequence pump also shows a wattage curve showing that head pressure does effect efficiency. I may be wrong, but I am trying to think of ways to keep my CL pumps as high off the floor as possible.

For a simple amswer there are three components to losses in pumping applications.

The first is lift. The height you have to raise the water. In a closed loop that distance is 0 since you are pumping from and to the same body of water. For your return pump it is from the top of the water surface in the sump to the top of the water surface in the tank. Unless you returns are out of the water then it is to the return point.

The second is flow losses. These are the ones that are due to the length of the pipe, size of the pipe, fitting and the flow through it. Shorter pipe has less losses than a longer pipe of the same diameter, with the same flow rate. A larger diameter pipe has less losses than a smaller diameter pipe of the same length, with the same flow rate. Less fittings have less losses. Slower flow has less losses through pipe of the same diameter than fast flow.

The third is the pressure differental and the suction and discharge. On a closed loop this is also 0 since you are pulling from the same body of water. When pumping from different bodies of water you need to look at it. (not really in what we do, but it is there)