How accurate is the GPH measurement by the Flow Sensors?

[static416]

I'm running 4 flow sensors. Two 3/4 in (HDRS-FM075) and two 1 inch (HDRS-FM100).

In all cases, the measured flow seems about 1/3 to 1/5 of the flow that I'd expect.

• One 3/4" is connected to a Jebao DCP-10000 - Max 2600GPH
  • This one shows 530 GPH at full power in a short closed loop.
  • It is pushing water through 3/4 tubing to a Y fitting (not T) which splits flow to two Aqua UV sterilizers, and then immediately back into the sump.
  • Total vertical lift is about 2 feet at most, and it seems like the head would be low.
  • 500 GPH on a 2600 GPH max would be about 16 feet of head. Which is about 4-5x what I'd expect.
• Two 1" are connected to Ecotech M2s, which are separate return pumps for two tanks - Max 2000 GPH
  • Both show about 625 GPH at full power
  • It's 1" tubing almost straight up from the sump to the return ports. Maybe 4 feet vertically.
  • 625 GPH of flow correlates to 12 feet of head in their flow chart. About 3x what I'd expect.
• The last 3/4" flow sensor is also on a Ecotech M2 - Max 2000 GPH
  • This one reads 225 GPH.
  • The setup here is way more complicated, and likely a lot of head pressure, but still about 1/3 what I'd expect.

Do others have a standard multiplier they apply for these flow sensors?

In most cases I only really care if it's 0 or not. Or the trend over time. But with the UV, I'd like it to be accurate.

Measuring with a bucket is my next step, but I'm wondering if there is just some simple correction factor I can apply?

 

[thom_smith]

The Jebao is rated 2600gph with 1 1/2". Believe the Ecotech M2 is 1 1/4". You're reducing to 3/4" and adding significant head pressure by ~50% diameter reduction. The Hydros sensor is a commonly used Hall-effect sensor. It may not be dead on but would bet it is a whole lot closer to planned bucket test results than your estimates. Most people don't take into account head loss with reduced plumbing. And it's very difficult to calculate to boot.

 

[static416]

Hmm, that makes a lot of sense.

I'll just do the bucket test and see. It's just not fun because it's PVC flex and not very movable. But you could be right.

Also, the lack of similar posts anywhere complaining about accuracy makes me think this is a me-problem.

 

[static416]

You're reducing to 3/4" and adding significant head pressure by ~50% diameter reduction. The Hydros sensor is a commonly used Hall-effect sensor. It may not be dead on but would bet it is a whole lot closer to planned bucket test results than your estimates.

I actually took many fluid dynamics classes in engineering like 20 years ago, and have almost completely forgotten all of it. But you prompted me to remember that there are ways to calculate this.

I looked up the quoted head pressure for the Jebao, converted to bar using this then used that along with this caluator to get flow rate.

And wouldn't you know it, you're right.

The number isn't precise, because my "length" for the pipe is hand-wavy, but it's actually pretty close to the numbers I'm seeing for the Hydros sensor. At least in the neighborhood.

--

Definitely am running too little flow through my UV though. Fortunately the runs are short and relatively easy to change, so I guess I'll up-size the piping.

Thanks!

 

[Shred5]

Allot of the pumps in the hobby have graphs showing head pressure loss, they usually do not for bends. I know their used to be a thumb rule in the hobby. It also varies by the diameter of the piping.

I think it is for every 90 degree add one foot of head pressure.

Are they dead on no but I feel they are pretty close. I would also clean them from time to time.