Pentair UV Killing Flow

[ca1ore]

Keep in mind that most of the common DC pumps are designed for flow, not for pressure. Put restrictions on them like 1/2” barb fittings or the 1/2” Neptune flow meter and you’ll lose a ton of flow. Pressure rated pumps like iwaki or PanWorld will do far better, but then you’re dealing with an external.

 

[ca1ore]

So the 1/2 inch sensor is only good for bio pellet reactor, gfo and other very slow flow devices.
Bummer!

IME, the FMK is sort of useless because the 1/2” flow sensors have such limited application. Better, in my view, to get the FMM and sensors separately.

 

[Dj City]

my return pump is rated for 2900 gph, it goes through 1.5" pipe, through my 2" flow meter, through my 57 watt UV and to my tank. Flow is only 950 gph. It's just the way the pumps work. If you look at the pump curve it doesn't take many feet of head pressure for the pump flow to plummet.

Yeah but the 1/2 flow sensor is only good for 250gph.
My pump does not drop THAT much in flow.

 

[JPK_Esquire]

IME, the FMK is sort of useless because the 1/2” flow sensors have such limited application. Better, in my view, to get the FMM and sensors separately.

I though the same thing and bought the FMM and two 1" Flow sensors (which I read are terrible and eventually fail) separately. I bought them not so much to monitor flow long term, but at setup making sure I was running enough flow through the sump. I'm currently running the COR20 at 30% (approx. 500 gph) and COR15 at 40% (approx. 500 gph). If I turn those up to like 70% or 80%, the flow doesn't get exponentially higher, the pumps just get louder. 1,000 gph running through the sump is more than enough for me (5.5x).

 

[CuzzA]

I had probably less than 18 inches of head height (just up and over the top of the sump) and then directly down into the UV, run the length of the UV (4 feet or so) then up the same 18 inches and back into the sump. I was using tubing so no elbows etc. That short 18 inches on both sides (so total 36 inches of head height) lost me 1,000 gph? I think it is the barbed fittings, just haven't had a chance to confirm yet. As I described above, when I just pump using the 3/4" hose, I got 1,200 gph with the exact same front-end head pressure.

It's not just the head height, there's a ton of friction loss in a UV housing.

 

[Bob Lauson]

Generally, it is better to control the flow on the outlet side of these types of pumps. You should generally never control centrifugal pumps (which all of these are) on the suction or inlet side.

 

[jlts21]

vertical feeding top to bottom. Flow should be controlled on the inlet, not the outlet. If my suspicions are correct and you have it oriented wrong, it is likely trapping air reducing the flow.

incorrect. if mounting vertically, you want the flow to run from bottom to top

 

[ca1ore]

(which I read are terrible and eventually fail)

Everything fails eventually LOL. Not terrible, but the 1" sensors do require occasional disassembly and cleaning. I have 6 of them and did have one fail and get replaced under warranty.

 

[Bob Lauson]

I though the same thing and bought the FMM and two 1" Flow sensors (which I read are terrible and eventually fail) separately. I bought them not so much to monitor flow long term, but at setup making sure I was running enough flow through the sump. I'm currently running the COR20 at 30% (approx. 500 gph) and COR15 at 40% (approx. 500 gph). If I turn those up to like 70% or 80%, the flow doesn't get exponentially higher, the pumps just get louder. 1,000 gph running through the sump is more than enough for me (5.5x).

One thing also to note, with these types of pumps, if you are controlling the flow on the inlet or suction side then the "pumps just get louder" is likely due to the fact that it is experiencing cavitation which is not just causing excess noise but can result in severe damage to the pump. That is a critical reason why inlet control is generally a bad idea. You want the flow to the pump be as open and clear as possible and you want the inlet to the pump to be below the water level of the tank you are pumping from.

 

[Bob Lauson]

When I plumbed in my Pentair UV40 I had dedicated pump for it and did a bucket test to get the flow I wanted. My flow control was simply PVC plug at the end of the plumbing as it discharged into the tank. I drilled a small hole in the plug and measured the flow. To get the ideal flow, I simply drilled the hole a little bigger, re-did the bucket test, and continued the process until i had the desired flow rate.

 

[Dj City]

This might sound uneducated but...

The hole on the 1/2 inch barb fitting is way smaller than the opening on the 1/2 inch pipe.
Is that just me and my perseption or is that how it is?

 

[JPK_Esquire]

This might sound uneducated but...

The hole on the 1/2 inch barb fitting is way smaller than the opening on the 1/2 inch pipe.
Is that just me and my perseption or is that how it is?

I’ve had the same thought. I’m using 3/4” pipe and barbs, but same issue. The whole for the barbs is smaller and I think that’s where the flow loss is coming. Only way to find out...

 

[Dj City]

I removed the UV and had the flow going through the manifold to the 1/2 inch barb and tubing.
The flow sensor is now reading 302gph. This is a reading from the 1/2 inch flow sensor.

If I can SAFELY figure out a way to remove the barb from the manifold and test flow again without the barb, I would be very interested in what I get from a 1/2 inch pipe.

I think what I will wind up doing though is hard plumb the UV to 3/4 pipe to the manifold and use a 1 inch flow meter.
I wonder if that would work as far as Apex reporting correct flow since it will be thinking I have a 1 inch pipe instead if 3/4.

 

[ShpwrkReefsS]

I found this thread helpful as I am about to start plumbing my new build. I bought a
Pentair 25W UV for my 90G (120G system) and planning to run a separate pump Sicce 1.5 (357gph) with 3/4" tube through a 1/2" flow meter. The UV will be mounted vertically to the back of the stand and flow bottom to top. I was primarily only interested in protozoa flow rates @ 79/131gph. After reading this I will make some changes...

1) Plumb with 3/4" PVC
2) upsize to 1" flow meter
3) upsize pump to do both protozoa and algae (tune accordingly with gate valve)

Question: would you install the flow meter at the inlet or outlet side of the UV sterilizer??

 

[Bob Lauson]

I doubt is really matters where the flowmeter is plumbed. I don't know the detail of the particular flow meter you have but they usually require a certain length of straight pipe before and after to get accurate readings.

 

[Dj City]

I found this thread helpful as I am about to start plumbing my new build. I bought a
Pentair 25W UV for my 90G (120G system) and planning to run a separate pump Sicce 1.5 (357gph) with 3/4" tube through a 1/2" flow meter. The UV will be mounted vertically to the back of the stand and flow bottom to top. I was primarily only interested in protozoa flow rates @ 79/131gph. After reading this I will make some changes...

1) Plumb with 3/4" PVC
2) upsize to 1" flow meter
3) upsize pump to do both protozoa and algae (tune accordingly with gate valve)

Question: would you install the flow meter at the inlet or outlet side of the UV sterilizer??

Don't upsize the flow sensor.
BRS asked Terrance of Neptune Systems about this and he told them it will give inaccurate info because it will calculate for a 1 inch pipe. The flow will be different in the 1 inch sensor than it will be before and after the sensor.

 

[ShpwrkReefsS]

Don't upsize the flow sensor.
BRS asked Terrance of Neptune Systems about this and he told them it will give inaccurate info because it will calculate for a 1 inch pipe. The flow will be different in the 1 inch sensor than it will be before and after the sensor.

Wouldn't that be the same case for the 1/2" sensor then...? If running 3/4" pipe or tubing and reducing into and increasing out of a 1/2" sensor?

 

[Dj City]

Wouldn't that be the same case for the 1/2" sensor then...? If running 3/4" pipe or tubing and reducing into and increasing out of a 1/2" sensor?

No. Once it gets reduced, it's reduced.
I went from 3/4 pipe and tee'd to 1/2 inch. From the 1/2 inch pipe came the flow sensor then out to 1/2 inch barb fitting.
If there were a change AFTER the 1/2 back to 3/4 it would not work. So going from 3/4 pipe to 1 inch sensor back to 3/4 pipe won't work.
BRS and Neptune said anything other than the correct size pipe to flow sensor won't work.

 

[DCR]

No. Once it gets reduced, it's reduced.
I went from 3/4 pipe and tee'd to 1/2 inch. From the 1/2 inch pipe came the flow sensor then out to 1/2 inch barb fitting.
If there were a change AFTER the 1/2 back to 3/4 it would not work. So going from 3/4 pipe to 1 inch sensor back to 3/4 pipe won't work.
BRS and Neptune said anything other than the correct size pipe to flow sensor won't work.

This just is not true. The velocity in the piping will change when you change the piping size, but the volumetric flow rate is the same. GPH is GPH regardless whether the sensor size is the same as the pipe size, upstream or downstream.

 

[Dj City]

This just is not true. The velocity in the piping will change when you change the piping size, but the volumetric flow rate is the same. GPH is GPH regardless whether the sensor size is the same as the pipe size, upstream or downstream.

This is just wrong.
The sensor reads what neptune programmed it to read. The 1 inch sensor thinks it's on a 1 inch pipe and will read as such.

Go argue with Terrance of Neptune systems if you don't like the answer.