1.5" Return Pipe + 3/4 Loc-Line Restricting Flow

MarylandTang · Oct 29, 2017

Hi all, I wanted to check my math on how many 3/4 Loc-line outlets I would need to keep from restricting the flow in a 1.5" pipe, which has nothing but 1.5" all the way back to (and including) the return pump. So, to be clear - 100% 1.5" pipe, but then it will branch off into a few different sections to flow into the tank.

If there was ONLY one outlet going from the 1.5" pipe to a single 3/4" Loc-line output, then the flow could not be more than a 3/4" Loc-line opening would allow. But, if there are multiple, each one could have full pressure, thus not reducing the power of the theoretical full power 1.5" pipe flow. Make sense?

An example pic (not mine) of what I'm thinking:

ca1ore · Oct 30, 2017

Even if you calculate the number of locline outlets to equal the cross section of 1 1/2" pipe, you're not going to get 'full power' with all those elbows and adapters.

MarylandTang · Oct 30, 2017

Right, I know that the elbows, adaptors, head length all reduce flow - it was more to call out that 3/4 pass through is far less than even a reduced, yet still large 1.5" flow.

Assuming the standard loss, I wondered if having 2, 3, or 4 sets of 3/4" locline would keep from having an restriction issues on that side of the piping equation. Thanks!

ca1ore · Oct 30, 2017

You'd have to do the math. My suspsion is that you'd need more than 4 locline openings to retain the same flow diameter.

Potatohead · Oct 30, 2017

At low pressure, 1.5" pipe will flow about 2100 gph. 3/4" will do 660gph, so you basically need three of them.

TheEngineer · Oct 30, 2017

I'd take a slightly different view of this and start with the pump. Flow through a 1.5" sch40 pvc pipe at average pressure (20-80PSI) is 4830 gph. What's your pump rated at?

EDIT: @Potatohead and I were typing at the same time

Same data table, just at different pressure. High pressure would be 7500 gph, but I don't think our pumps can push anywhere near that hard.

ca1ore · Oct 30, 2017

Potatohead said:
At low pressure, 1.5" pipe will flow about 2100 gph. 3/4" will do 660gph, so you basically need three of them.

I haven't used locline in years, but doesn't it restrict down even further than an open 3/4" pipe?

Potatohead · Oct 30, 2017

ca1ore said:
I haven't used locline in years, but doesn't it restrict down even further than an open 3/4" pipe?

It's possible, I don't know for sure. Good catch though.

MarylandTang · Oct 31, 2017

My goal is to keep from adding an extra back pressure to whatever the pump is able to put out, and make as even of a water distribution as possible.

If one end of the spectrum is the return line into a single outlet head, then the other end of the spectrum would probably be something like this, where I could have 8 feet of slit pipe across the top of the tank. Water should be able to spill out somewhat evenly across the entire surface, and assuming it was a half inch above the waterline, there would be no possibility of a reverse siphon if the pump loses power.

The above image is more of a proof of concept. Any thoughts on the design over an 8' tank?

TheEngineer · Nov 1, 2017

You would need to vary the width of the slit to get even flow. Thin at the start and wider at the end. Search for spray bars and you’ll see some great examples of a similar approach.