FMK Flow sensor placement

[Yates273]

I am entertaining the idea of purchasing the FMK. I have searched and read different threads of placement but I’m curious. Should I place the 1” flow sensor just above my return pump which is in the sump. This would be easy to clean if needed or would it be more beneficial to place it right before the return on the rear of the tank? The return is about 3 ft above sump. Will my reading be that much different? TYIA

 

[lapin]

Each will give you different readings. I would go for the easy to to clean. As long as you get a constant reading it really does not matter where it is placed. Most tanks use power heads in the tank for the main source of flow

 

[Yates273]

Tnx. Just ordered kit along with a leak detector pad and pmup. I already have two power-heads that provide good flow also.

 

[KStatefan]

Why would the location of the sensor change the readings?

 

[chiefifd]

Flow would depend on changing distance from pump, elbow/elbows after the pump or maybe the elevation change... Those are the oblivious ones that come to mind.

 

[KStatefan]

The flow will be equal thru out the pipe. Fittings and height will reduce the flow but it will be reduced the same everywhere.

 

[chiefifd]

Friction plays into all this.
The relationship between flowrate and pressure drop
The relationship of flow to DP states that the pressure increases by the square of the value of flow. If the flow doubles, the DP increases by four (2 x 2 = 4). If it triples, DP goes up by nine (3 x 3 = 9). If you cut the flow in half, the DP decreases by a factor of four (1/2 x 1/2 = 1/4). Keep in mind that the DP shown in Figure 2 is per 100 feet of straight and perfectly smooth pipe. A six-foot run of half-inch copper pipe to connect a 2.5-gpm shower off a three-quarter-inch line decreases the pressure by about 1 psi. On the other hand, if you run a half-inch line from the kitchen to the barn 200 feet away, you may not be able to fill a bucket with water before the cows come home.

Inside the pipe, flowing water causes an energy loss due to friction. It takes energy to push past the pipe surface, no matter how smooth the pipe is. This reduces the pressure available to push water out the end of the pipe. The pressure loss due to friction occurs at every point along the pipe; when water starts to flow, the pressure is highest at the source and decreases every inch along the way and is lowest right at the tap. If we wanted to move 3 gallons per minute (gpm) through a half-inch-diameter pipe, 100 feet long, we might lose about 7 psi of pressure. If the pressure at the beginning of the pipe is 60 psi, the pressure at the end would be 53 psi. Flows (or flowrates) are measurements of the volume of water that comes out of the tap every minute. Hydraulic design must take into account the dynamic pressure available under flowing conditions at the point of use and not the static pressure available in a non-flowing condition.
Granted most of us are not running long lengths of pipe or tubing, friction does play a part in all this. GPM loss is probably minimal in our aquarium setting but it is there.
This principle is used by fire departments, from fire hydrants to fire trucks then relay pumping to other fire trucks to boost pressure and volume, if the fire hydrants are at some distance or elevation.

 

[KStatefan]

We are talking about flow not pressure. Yes friction plays a roll in how much flow but it will remain equal throughout the system. If there is 100 gph coming out of the pump there will be 100 gph going into the pump.

 

[chiefifd]

Flow is how much water comes out of a section of hose, even on a horizontal plane. There's friction loss, granted maybe not much in a short run of one-inch tube, there is a loss of flow.
Your thesis "100 gph coming out of the pump there will be 100 gph going into the pump" would be correct. But ten feet down the pipe/tube there won't be 100 gph flowing, friction is something you can't overcome.
Again, the loss for out purposes is small, but there is a loss of flow.

 

[KStatefan]

How would there be 100 gph coming out and 100 gph going in but not 100 gph 10 foot down the not be?

 

[chiefifd]

There is friction loss in the pipe, even if it's on a horizontal plane. This is for flowing water. Static water in a pipe under pressure will stabalize, the longer the pipe the longer it will take to stabalize the pressure. When the pipe is opened you'd see a slightly stronger stream until the friction loss catches up. The stronger stream would only be apperatent for a second before falling to the friction loss.
I'm not a fluid engineer, I do know that water flowing along a pipe/tube has friction loss. Again flowing water has friction loss. Static water not-flowing would have a constant pressure. It might take a short or long while to build up the static pressure depending on lenght of pipe/tube. When the static pressure is released, the pressure at the open end of the tube/pipe will be less.
I was only trying to give an example that there is a difference in flow thats effected by friction. In our purposes, that friction loss on a horizontal plane is very minimal, until you start adding elbows and rises.
Hope this helps...

 

[KStatefan]

I never said there is not fiction loss in a pipe there is but it does not cause the flow to be different at different places along the pipe. Increasing the friction will cause the flow to go down but along the whole system. Flow will be the same at all places along the system.

 

[chiefifd]

If water is flowing, yes there is less flow every foot along the pipe. Think about it, there's friction to overcome, that include the weight of the water being pushed.
In our world of short pipe runs horizontally the loss is very minimal.
Real world example about water flow that I would see as a firefighter
Friction loss occurs when water passes through a hose. Hose length, diameter, and GPM (volume) all affect friction loss. As water passes through a hose, friction between the water and the inside surface of the hose causes turbulence, which slows the water. The results in a PSI drop (pressure loss) at the other end of the hose. The higher the gpm passing through a hose, the more turbulence and friction loss will result. Here's a calculator that shows friction loss, even in pipe as small as 3/4 inch.

Friction Loss Calculator

Enter the hose diameter, hose length, GPM & press the 'calculate' button to get the friction loss measured in PSI.

www.frictionlosscalculator.com

Maybe I'm missing the point here totally, but water, as is moves along a pipe, slows down and is moving slower than at the pump outlet.

 

[DCR]

Maybe I'm missing the point here totally, but water, as is moves along a pipe, slows down and is moving slower than at the pump outlet.

You are correct that friction reduces the flow, but it affects the entire water column of flow like friction would affect the speed of a train, and the flow is reduced the same everywhere in the circuit. For an incompressible fluid, like water, the flow has to be the same at every point in the circuit. There is no place for the excess to go. Otherwise you would be pumping more water out of your sump than was being returned and it would go empty. Mass is conserved.

 

[Ribo15]

Maybe he runs a manifold off the pump and that’s the part he missed!

 

[KStatefan]

@DCR responed better than I could

 

[chiefifd]

My apoligies I stand corrected.........
Source University Nebraska-Lincoln:
Since the liquid is incompressible and there are no places in the pipe where the liquid can be stored, the volume of liquid which flows through any plane perpendicular to the streamlines in any interval of time must be the same everywhere in the pipe.

 

[lapin]

My apoligies I stand corrected.........
Source University Nebraska-Lincoln:
Since the liquid is incompressible and there are no places in the pipe where the liquid can be stored, the volume of liquid which flows through any plane perpendicular to the streamlines in any interval of time must be the same everywhere in the pipe.

I learn something new everyday
Thanks