Will a bigger feed line help?

[dbeitz1891]

Folks I'm buying a memprotec 350H the feed line heading to the pump is a 3/4". I was incouraged to put a 1" from my tank to that line and my question is if it's necessary because it only gets necked back down to 3/4" like I said.

[Maplewalnut]

I have a 1.5 inch line feeding my 250 gph RO. The larger line helps purge air at start up. 3/4" seems very small. Not much price difference, make sure you put a strainer upstream of pump to course filter any mouse presents.

[BAP]

Bigger line helps with friction losses to maintain full volume to the pump.

[dbeitz1891]

Yup have a screen right before sap enters pump. But yup the feed line and both exit lines are 3/4". Only thing I was worried about going to a bigger line was losing suction power due to a larger surface area.

[wiam]

My Memtek 250 had 1 inch in. Bigger is better on suction. You won't lose much reducing to 3/4 right at the pump. Limiting factor of most pumps is suction size. Little off topic but at a fire department pumping class I was shown hot that if you add a 3" suction line to the 5" that is standard you can get almost 1300 gpm out of a 1000 gpm pump.

[maple flats]

You lose more with 3/4" than 1" or even 1.5". It is all related to line friction, the larger the suction line the lower the line friction.
Back when I had a professional irrigation company set up my first irrigation system to irrigate strawberries for frost control, I had a Hale Fire pump. It was a 3" pump, but the suction line was 4" to get more flow to the pump. This is the same idea, just in a smaller size.

[dbeitz1891]

Right makes sense I was just curious why they haven't been oversizing intake lines right from the factory then. If nearly everyone does it and it helps it would just make sense to do it that way

[DoubleBrookMaple]

Simply put, it's like this...

We define volumetric flow rate V̇ (ie. volume of fluid flowing through the pipe per unit time) :

V̇ = Av

therefore

V̇ = πr2v

where

r = radius of the pipe (for a pipe of circular section, the internal radius of the pipe).
v = mean velocity of fluid flowing through the pipe.
A = cross sectional area of the pipe.
In long pipes, the loss in pressure (assuming the pipe is level) is proportional to the length of pipe involved. Friction loss is then the change in pressure Δp per unit length of pipe L

\frac{ \Delta p }{ L }.
When the pressure is expressed in terms of the equivalent height of a column of that fluid, as is common with water, the friction loss is expressed as S, the "head loss" per length of pipe, a dimensionless quantity also known as the hydraulic slope.

S = \frac{h_f }{ L } = \frac{ 1 }{ \rho \mathrm{g} } \frac{ \Delta p }{ L } .
where

ρ = density of the fluid, (SI kg / m3)
g = the local acceleration due to gravity;

The answer is, yes a bigger feed line helps.
Now the question is... How much does it really matter with all the variables?

[DoubleBrookMaple]

Here is an statement from a "white paper" from Pentair on suction side pipe sizing...

"A rule of thumb is: With fractional size (4” or smaller) pipe using a suction pipe that is two sizes larger than the pipe
diameter at 5 FPS provides the most efficient use with the least friction loss. On the suction side this means more
vertical lift. Overall, this makes the pump work easier and better. It is simply more efficient."

Two sizes?
Like my feed pump has a 3/4" outlet (pressure), and two sizes larger inlet suction side at 1 1/4" ?

http://www.sta-rite.com/resources/images/20504.pdf

[dbeitz1891]

Thank you for the input. I'm going to go with 1". Only had to pull it up about a foot. If I run into any issues then I'll have to reevaluate

[wiam]

It is best to have the tank higher than the ro input.

[dbeitz1891]

I know it is, I'm going to build another platform next year. Nothing like in season change lol