Proper use of an Apex Flow Sensor?

[DavidJTawil]

I'm currently plumbing a 150 gallon tank with a bean animal overflow. On the main drain I'll be using a Clarisea SK5000 which has a maximum flow rate of 1320 gph. I purchased an apex 1 inch flow sensor to put on the Clarisea drain line. Is it a bad idea to put a flow sensor on the drain line? Will it get clogged easily? Has anyone ever used a flow sensor on a drain line before?

On a similar note, taking into account some laws of fluidynamics ( Bernoulli's Equation and the equation of continuity), R, the flow throughout the pipe, should be equal at any point in the pipe. Therefor, wouldn't it make no difference where a flow sensor is placed in the loop. I ask because, while tuning my UV sterilizers, should I crank the pump up until my flow sensor reads my desired flow rate or should I be taking into account that there is an elbow right after the flow sensor. Attached below is a picture of the uv setup I'm referring to.

 

[SuncrestReef]

Flow sensors on a drain line will have a higher probability of getting clogged over time compared to one that is after mechanical filtration. As long as the sensor is in a place for easy access, cleaning it periodically isn't very difficult.

Here's what my 1" flow sensor connected to my return line (the cleanest possible location in my plumbing) looked like after 3 years without cleaning:

Read this FAQ about sensor installation and placement: https://forum.neptunesystems.com/showthread.php?18184-Flow-Sensor-Installation

 

[NeonRabbit221B]

The elbow will throw off flow rates considerably. Luckily paddlewheel types are not as susceptible. I would create a scale and compare it to known manufacturing outputs. Should be close.

 

[DavidJTawil]

I would create a scale and compare it to known manufacturing outputs. Should be close.

Do you mind elaborating?
Much appreciated,
David

 

[TexanCanuck]

Hey there,

As @SuncrestReef has already pointed out, it is important to note that the Apex flow sensor is a "paddlewheel" sensor. This is important because this type of flow measurement device has some well documented engineering limitations. (I come from the refining industry where flow sensors are used everywhere, and this is a common concern)

Specifically, these types of flow sensors will give very inconsistent results if used in turbulent flow or two-phase flow (i.e. air and water at the same time, or water and solids). These sensors will also give inconsistent results if there are any significant amount of solids in the flow (i.e. algae).

So while you CAN use it in your drain line, you will not get accurate results if the drain line is not running at a full siphon, or if there are occasional solids that pass through the line.

Also, while you are right that the volumetric flow rate through a continuous pipe network will be constant at all points in that network, this sensor does not volumetric flow rate ... it measures average linear velocities and then calculates volumetric flow rates based off an assumed pipe diameter and the assumption of laminar flow. Therefore, this meter will give different readings at different points in that network due to high levels of turbulence - in particular, immediately after elbows, T-connections, pipe diameter changes, etc ... in these areas it is quite common to get localized flow recirculation (eddies) that will throw off the meter.

So the best practice is to install this meter in the RETURN line to the tank (so that you are relatively confident there will be no entrained air or solids in the line), and to install it AT LEAST 5X THE PIPE DIAMETER FROM ANY FITTING, ELBOW, OR CHANGE IN PIPE DIAMETER. In my experience, if room allows I would aim for 10x the pipe diameter.

Example - if you have 1" pipe, make sure the meter is no closer than 5" from any elbow or any other fitting.

Make sense?

 

[NeonRabbit221B]

Do you mind elaborating?
Much appreciated,
David

My thought is that if its a DC pump that those %/voltages have a published flow rate with known head pressures. If the output is wonky or not matching up 1 for 1 then you can make sure that it atleast scales correctly.

For example at 10% pump speed the manual says you should see 100 gph but you actually see 85 gph
and at 50% pump speed the manual says you should see 500 gph but you actually see 425 gph then you are golden because it scales correctly... Might be going overboard with this....

As @TexanCanuck mentioned the distance from elbows/valves should be 5x diameter at least so you will likely need to replumb it