how to calculate pump flow rate loss from vertical lift

[venzi]

I'm pretty sure this is the case, but just wanted to confirm: is there a reduction in flow rate by having a pump shoot the water up a vertical pipe vs. horizontally?   I'm experimenting with placing a pump at the bottom of the tank instead at the top and I realized that perhaps there'll be a loss in overall flow b/c the pump has to shoot the water up.  Is there a simple formula to calculate the flow loss (assuming there is a flow loss)?

So for some concrete stats, I have a 20H tank.  The pump is rated at 50gph and 2ft of head and the barb is 1/4" ID.  The length of the vertical tubing would be roughly 12".  So if this is the setup, would the flow be reduced to like 25gph instead of the full 50gph?  I'm just looking for rough ball park figures.

I suppose I could try running a live experiment as well.  Thanks.

[nabokovfan87]

On 8/11/2022 at 4:43 PM, venzi said:

I'm pretty sure this is the case, but just wanted to confirm: is there a reduction in flow rate by having a pump shoot the water up a vertical pipe vs. horizontally?   I'm experimenting with placing a pump at the bottom of the tank instead at the top and I realized that perhaps there'll be a loss in overall flow b/c the pump has to shoot the water up.  Is there a simple formula to calculate the flow loss (assuming there is a flow loss)?

The simple way to look at it.... when the water is flowing vertically, you have gravity pushing it back towards the bottom of the pipe.  If the pump is at the bottom of that pipe, that's just the actual force of backpressure.  If your pump is at the top of that vertical run, you have to pull the water up against gravity.  If it's horizontal you have to push it along the pipe and your force against the pump is the friction / resistance of the water against the surface of the pipe itself.

I'm sure there is a sump expert around here that can help us with the numbers! 🙂

[venzi]

So I just did a rough experiment to get ball park figures.  TLDR  a 50 gph rated pump did 40gph w/ minimal vertical lift (approx 4" vertical lift) and 31.6 gph with 12" vertical lift.  There's still enough pressure coming out of the hose to create turbulence at the top of tank and if I attach some kind of adapter to end of the hose, then there'll be even more pressure.  So all in all, I can prob live w/ these numbers, but later on I might consider a stronger pump perhaps.

• Setup

  • Used 5 gallon home depot bucket

  • Pump rated at 50gph with 2 feet head.

  • Outlet attached to 26” long tube

  • Measured how long it took to remove 1 gallon of water from the bucket into a 1 gallon water bottle

• Result for 12” vertical lift

  • Pump was placed at the bottom of the bucket and it measured roughly 12” from top of pump to the top of the bucket (pretty much close enough to the vertical lift that would happen in my 20H tank)

  • Regardless of pump orientation, it took 1min 54 sec (1.9min) for 1 gallon (aka 31.6gph)

  • Using a outlet 5V charger or USB battery bank did not change results (all within margin of error)

• Result for nearly horizontal (minimal vertical lift maybe 4 inches of vertical lift)

  • This was tricky to do w/ the 5 gallon bucket, but I tried to tilt and hold the bucket on its side as much as possible to prevent excess vertical lift in the tube

  • 1.5min for 1 gallon (40gph)

[Pepere]

If pump is at bottom of water column pushing up a pipe to top of water column but not above the water column, head loss is limited to frictional losses in the pipe itself an no different than horizontal.  This is because weight of the water above pump adds pressure.

 

a pump with 2 feet of head would only be able to raise the water 2 feet above the surface of the water.  However a pump with 2 feet of head 10 feet down in a pool would still be able to push water up a pipe from the bottom of the pool to almost 2 feet above the level of the water. I say almost because the length of pipe would impose some frictional head loss.

[Pepere]

1/2 inch plastic pipe loses 2 feet of head per 100 feet of length when flowing at 5 gallons per minute.

[venzi]

On 8/12/2022 at 2:31 AM, Pepere said:

If pump is at bottom of water column pushing up a pipe to top of water column but not above the water column, head loss is limited to frictional losses in the pipe itself an no different than horizontal.  This is because weight of the water above pump adds pressure.

wow thanks for this bit of knowledge.  That changes everything. 🙂

On a related note, @Peperedo you know if a 90 degree elbow on the pump inlet has any significant impact for flow?  I know that adding a 90 degree elbow at the output will impact that pressure for sure.

 

Edited August 12, 2022 by venzi

[Pepere]

Aright elbow is the equivalent to adding three feet of the same size of pipe.

Impact is the same on inlet as outlet.

[venzi]

On 8/12/2022 at 10:36 AM, Pepere said:

Aright elbow is the equivalent to adding three feet of the same size of pipe.

Wow.  So whether the elbow is at the inlet or outlet side, it'd just be the same as adding 3 ft of pipe?    For some reason, I thought it was more impact.   Oh you know what it is.  I'm thinking back to my days when i used to water cool my PC and all those pumps/tubing was outside of the water column 🙂 

Things are so much simpler when everything is inside the water column.

[Pepere]

No,  the right angle does not matter in or outside of the water.  It is simply a function of fluid dynamics and turbulence induced by the angle and frictional losses.

The affect of the water column is you are pumping from an area of higher pressure at bottom of tank to lower pressure at top of tank. This offsets the head loss from the height change.