Extending Magnum HOT tubes for deep duty. Overwork motor?

[knifegill]

I am aware of most of the forces that play inside of piping. But my mind can't quite get a grip on whether or not extending the intake and output of a sealed Magnum HOT downward to a lower water line would stress the motor out and slow down the flow or not. I know that gravity pulling the exiting water ought to compensate for the force required to lift it on the intake, but it's a negative pressure environment, so does gravity get to play in that hose or not?

I would be putting the HOT on my sump once it's all kosher and stable.

 

[boldtogether]

You will be placing greater headpressure on the pump potentially deminishing the output.The added pressure the deeper the intake tube goes in the tank, in my mind would actually increase the flow up the tube, but if you leave it at the same level in the tank, the only water weight advantage will be the extra weight the extra pipe volume will give on the outside. Your filter is useing gravity(siphon) to aid in moving the water and it is much easier to start flow with a deeper placed downtube as the water doesnt have to fight its own weight, as much, up the down the tube. The added weight/pressure of the deeper water pushing on the moving water going up the tube would, I think, make the water move easier.
The water will then seek its own level which will be the waterline in the tank and the pump is just ment to give that final push up and over.
Centrifugal pumps only push, they don't suck, at least not that much, so the added weight of the water in the return line will push against the pumps impeller, decreasing flow(increased head), but, the increase in the siphon pressure may overcome the added head. I don't know if just a few inches will change much...try it out. I think the only problem you'll have will be with the return.
Just my 2¢.

 

[knifegill]

Oooh. That explains part of it. If a subscribe to the 'deeper water pushes more' concept, which I do, but not in this scenario since the return pipe will be at the same depth, thereby countering any 'push' that may have been provided on the way in. But the ends of the tubes won't be under much pressure, just the usual four inches or so. Most the extra line will be going through air to reach the distant water. Does this change things?

 

[Toby_H]

Short answer... adding longer intakes will not affect your flow to any measurable degree...


The larger factor will be the resistence of longer tubing having nothing to do with depth.


The "increased pressure" from the weight of water above the deeper intake will be countered by the increased weight of water within the tube. To prove this point, stick a pipe in water with the top end open. The water in the pipe will mature the water level outside the pipe. No higher, no lower.

To further verify this point... start a siphon from a body of water to the same body of water. the water in the tube will not move... lower one end deep in the tank, the water in the tube will still not move... regardless of the depth of either end of the hose, if both ends of a hose are in the same body of water, the water in the hose will not move...


FYI - I use extensions on my Mag HOT...

 

[knifegill]

The "increased pressure" from the weight of water above the deeper intake will be countered by the increased weight of water within the tube. To prove this point, stick a pipe in water with the top end open. The water in the pipe will mature the water level outside the pipe. No higher, no lower.

To further verify this point... start a siphon from a body of water to the same body of water. the water in the tube will not move... lower one end deep in the tank, the water in the tube will still not move... regardless of the depth of either end of the hose, if both ends of a hose are in the same body of water, the water in the hose will not move...

See, that's what I thought, too. But since I've never worked with an elevated and sealed system, I thought too hard about it. Thanks for the input, nc_nutcase.

 

[Toby_H]

When I first read your question I immediately knew the answer...

But I have to give BoldTogether credit. His explaination made me doubt my initial answer and I had to rethink it. As he pointed out, there are a lot of dynamic forces at work. But most of them cancel themselves out.

The additional friction of the length of the tube is the only force that will slow the flow, and the result would be very minimal with the small additional length you are considering within this application.

 

[vfc]

This 26" inflow extension did not impact the flow rate of the XP4 canister.

 

[knifegill]

Ah, but the entire thing is submerged. Mine will be suspended high above the water. Looks good, btw. I like the light blue. Why all the separate pieces?

 

[vfc]

Rena sells 3" extension kits.