Head Loss - Flow Calculation for Varios8

chrishet · Nov 3, 2020

Hi ya'll, I want to increase the flow rate between my display tank and sump. I was running a Varios6 and getting 375gph, according to an Apex Flow Meter. In addition to the return to my display I have a 2 lines running off my manifold each running 80GPH (also measured via flow meters). I am using .75 inch pipe with a height of about 3 feet. I am going through 7 90's, a gate valve, a check valve, and a 1 inch flow meter. I upgraded my pump to a Varios8 which is rated at 2700GPH with a max height of 18 feet. I am only getting an increase of 65GPH. I was surprised. I'm guessing all the 90's are creating too much head pressure. Thoughts?

metzer · Nov 3, 2020

Another factor that is limiting your flow is the 3/4" pipe. I had that issue with my COR-20s, the piping was the limiting factor.

With your flow meter installed you could try to remove the gate valve or check valve (assuming you have unions) and see if they are "robbing" any of the flow.

BZOFIQ · Nov 3, 2020

The 3/4" pipe is too restrictive for sure. DC pumps don't like to be restricted. Stick to nominal size for out pipe then split it.

Larry L · Nov 3, 2020

The Varios8 flow curve shows that it drops off rapidly as you increase the head pressure. At the moment I can't find the head loss calculator I usually use, but rule of thumb you're going to lose about 1 foot of head per 90 degree elbow, so between that and the actual 3 feet of head you're already at 10 feet or about 900 GPH per the flow curve. Add in the head loss from the 3/4" plumbing and all the other plumbing parts you mentioned and it's not surprising you're only getting in the low 400's.

metzer · Nov 4, 2020

I did an interesting test last night. I ran the test on some different tanks some with COR-20 and Vectra L2. My tanks are red seas and have an installed the loc-line adapter, the one that offsets it down into the water further. I removed those because they are kind of two additional 90 degree bends. Even though the tanks and return pipe plumbing is very different between all the set ups and both the COR-20s and Vectras have different Water Head/ft graphs, I increased my flow by 15 to 16%. I never would have thought that simple device was "robbing me" of 15% flow.

Just a tid bit of info of how simple things on return pump plumbing can make large differences.