Plumbing Flow Rate

[Mike T IL]

I have been trying to increase my flow rate to my Pentair SMART 40 UV. According to the documentation, a flow rate of 943 to 1574 is (*suggested/maximum). I originally had everything plumbed with 1" PVC with 1 flow sensor after the UV. I just made some changes to use 1.5" PVC going to the UV plus added a second flow sensor so I can see the flow rate going into and out of the UV. The results confuse me. I would have thought I would get greater flow rate by reducing the number of fittings and going from 1" to 1.5". My 2" flow sensor before the UV is showing around 620 GPH and my 1" flow sensor after the UV if around 650 GPH. Why would flow rate be greater in the smaller pipe? Also, are there any other modifications I can do to get the flow rate up the the Pentair recommended flow rate of 943 or greater for Algae & Bacteria. Here is how I currently have my plumbing setup.

 

[T-J]

90 degree elbows will slow water down. Most of my turns are through 2 45 degree elbows spaced out to help with flow.
Also, how much head height do you have on that pump? With 6 feet of head, you're looking around 1200gph max with that pump.
You may need a bigger pump.

 

[Mike T IL]

90 degree elbows will slow water down. Most of my turns are through 2 45 degree elbows spaced out to help with flow.
Also, how much head height do you have on that pump? With 6 feet of head, you're looking around 1200gph max with that pump.
You may need a bigger pump.

I am using an Apex Cor-20 pump which is rated for up to 2,000 GPH. I only have 3 elbows in the line. Would switching to 45 degree elbows make a huge difference? Also the height is around 4 feet from the pump directly up to the where the return is entering the tank. In total I am around 7 1/2 ft head height if I include the horizontal runs.

 

[KStatefan]

The flow rate in and out is the same you are just seeing error in the flow meters.

 

[DCR]

Adding the second 1" Apex flow sensor will restrict the flow significantly. I don't see in your original post where you stated the original flow rate.

600 gph is about all you can expect with a lot of 1" piping

 

[Reefer Reboot]

In accordance to the above diagram, any reduction in plumbing size, whether it is before or after the UV, will reduce the total flow capabilities.
Flow in will be equal to flow out (unless you have a leak ) so remove the smaller flow meter and replumb everything on the outlet side of the UV to 1.5".

 

[Reefer Reboot]

I am also assuming that the parts list on your diagram is correct and not what is labeled near the pictures, IE 1" elbows.

 

[Mike T IL]

In accordance to the above diagram, any reduction in plumbing size, whether it is before or after the UV, will reduce the total flow capabilities.
Flow in will be equal to flow out so remove the smaller flow meter and replumb everything on the outlet side of the UV to 1.5".

previous rate on the 1" flow sensor was around 580 GPH. You are also correct that 2 of the elbows are mis-labelled. They are 1.5".

The Apex Cor-20 has an output of 1 1/4 and the input/output of the UV is 1 1/2. So should I go all 1 1/2"? Or should I go 2" even though I would have to reduce to 1 1/2 to go into the UV and then increase it back to 2 going out of the UV?

Also, does the loc-line impact the flow since it is standard 3/4?

 

[Reefer Reboot]

It certainly wouldn't hurt to go with 2" plumbing. That will help reduce the tare (pressure/flow loss) of the fittings.
Yes, the loc-line will impede the flow rate. Remember, the pump has to push the water throughout all of the plumbing. So anywhere there is a restriction will affect the entire plumbing assembly.

 

[Snoopy 67]

The standard recommendation when using any pump is DO NOT reduce the outlet pipe size, use a valve inline to control flow. Up sizing will help with flow from the pump.

 

[DCR]

If you remove the outlet flow sensor and upgrade the remaining 1" piping to 1-1/2", you should be able to reach the suggested flow rate of 974 gph.

 

[1ocean]

i agree with everyones views...that why I have my UV pump in with my return pump in the return pump chamber.
It pulls water from the return pump chamber and puts it back in the return pump chamber. My thought here is that I do not have to buy a bigger pump since it is pulling water from the return chamber and putting it back.
Then the return pump which is much bigger is sending the UVed water back to the tank.
yes i realize that the UV water is not going back to the tank instantly, but it does all go back to the tank by the bigger return pump.
I am able to control the UV flow without a needed bigger pump. The UV pump also does not over flow the return chamber so 100% of all the UV'ed water does got back to the main tank...
I also attached a flow chart for pipe size...
Also remember even if you used much bigger pipes before and after the UV, it will not increase how much flow the UV can handle. The UV inside only has so much, say internal pipe size to allow for max water flow....
I hope this helps...
Have a great day