Calculating GPM Flow When Combining Multiple Sources

I must really be dense. If inflow is 1/8 gpm, how do you propose to get more out of the tanks than that?

Here's how it works.

The 4 gallon tanks are fed slowly with a constant flow of roughly .15gpm. It takes a while to build up the tanks but when they're filled, the system doesn't rely on anything other than the tanks to supply the water.

Picture 3 4-gallon tanks that never really have to give up more than half their supply in a day.

Now each (7psi pressurized) tank can supply .68gpm through 1/4" tubing. I'd like to combine the 1/4" tubes so that I can obtain 2 gpm out of a 1/2" spout.

With me here?

I'd like to know if there's a simple way to calculate how much psi I'd need to add coming out of a tank to add additional volume and how much.

Also, when combining 2 or 3 1/4" hoses into one 1/2" tube, is there and loss due to surface tension, voulme reduction, etc.

I'm not quite clear on what you are trying to accomplish.

To begin with, you don't get pressure (psi) out of a tank. The tank(s) will provide flow, the pressure will be a result of the resistance in your plumbing network and how much effort is being applied to the volume of fluid (pressurized with a bladder or the height of fluid (or both)). With with 3 tanks able to supply 0.68 gpm there is no way to get more than 2.04 gpm out (if that). With 4 tanks you won't get more than 2.72 gpm.

If you are asking to what pressure must the tanks be pressurized to increase the flow output of each tank so that you can get 3 gpm out of the sum of all flows, then that's a different story.

I assumed we could use the term "bladder" and tank interchangeably. The tank is filled with air at 7psi. This pressure causes the BLADDER to force the water out of the tank (gravity notwithstanding). We have the ability to increase the psi tank value but in doing so, decrease the maximum volume of water the tank can hold.

So the question was also; if 7 psi through 10 feet of 1/4" ID tubing yields .68gpm, how would we calculate the flow rate when the psi is raised?

Second, if you fed three 1/4" feeds in to one 1/2" faucet with a "YY" adapter, would the math be as simple as A+B+C?

Thank you for the clarification.

You are correct that the tanks won't hold as much water if you increase the tank pressure. But in going from 7 psi to 10 psi the difference would only be 0.12 gallons less water. So that's just a little more than a 3% loss in storage capacity.

if 7 psi through 10 feet of 1/4" ID tubing yields .68gpm, how would we calculate the flow rate when the psi is raised?

use what was given in the previous post.

if you fed three 1/4" feeds in to one 1/2" faucet with a "YY" adapter, would the math be as simple as A+B+C?

Theoretically probably not, but in a practical sense, yes.

This was a great answer. Thank you. You brought up a great point. The tanks have a static "pre-fill" pressure of 7psi. Once the system pumps water in, the pressure will read about 28psi (this is when the osmosis system shuts down).

I was surprised that 1/4" tubing at 100psi (the input feed to the system) provides flow of about 1.6gpm (give or take).

One additional question would be rather than summing together 4 or 5 tanks, would it be more feasible to slap on a 20g tank in the system and run a post booster pump?

Some manufacturers recommended against pumps after the tank. Not sure if I can imagine how a +30psi booster pump can damage the tank's bladder. Any ideas with that?

At the 28 psi pressure, those flows probably make sense. Unless the 3 smaller tanks are already part of some package, I like the single larger tank. A 1/2-inch connection sounds about right. Again a rough guess.

Why not get rid of the tanks and feed the [whatever needs the 2-3gpm] directly off the supply?

The only purpose for a tank is to let the level go up and down!

The initial flow supply is not high enough, the fluid is accumulated in the tanks providing a higher flow rate for short periods when demanded.

"Looking for a way to obtain a sold 2-3 gpm flow from a 1/2 pipe"

If you are using head pressure to insure a continuous flow at a rated volume that pressure has to be held constant. For as the tanks empty the head pressure will decrease reducing your flow rate. If you are depending on the 100psi 1/8 gpm flow to create this head pressure for continuous flow. The duration for use will be short. You are trying to get a lot more volume out then you are putting in. Storage capacity of the tanks and the duration in which you expect to obtain has to be known.

Would be easier to use a pump.

Can anyone answer these additional questions?

SYSTEM IN PLACE:

Purified water system (RO) capable of about 1 gallon per hour refill rate (25gpd) at 80psi municipal.
(2) 8psi pressurized 3.2g bladder tanks with ¼" outlets.
-Static system pressure 45psi.
-Dynamic system pressure, both tanks on, single ¼" faucet flow 30psi (1.4gpm flow-rate).
-Dynamic system pressure, single tank 10psi (.66gpm flow-rate).

QUESTIONS:

What is the maximum GPM rate capacity (and formula) of ¼" tubing (max of 100psi & no more than 10ft.)

--- The following questions assume that no more than 1 gallon will ever be pulled from the system at any given time ---

What formula defines this difference on flow-rate on the before mentioned system?

What effect, mathematically, would adding a third tank have on the system?

At what point would adding additional tanks have no effect (maintaining ¼" piping throughout)?

What effect would (from additional volume and decreased surface tension) adding a manifold connector (y adapter) combing both tank ¼" outlets in to single 3/8" standard line?