Need help getting equal flowrates??

[jackieboy]

Hey everyone...
I am new to this forum and I am doing my first fluid piping/pumping project. My question is either very basic/simple, or very complex. I am not sure at this point??

I have 3 reservoirs which are identical in size and dimensions. They are each filled with the same solution. The quantity of solution in each reservoir is also kept the same. All 3 reservoirs are also at the same height off the ground.
I have one pump (500 gal/min, 70ft).
I need to setup a piping/pumping system which will draw the solution from each reservoir at the same flow rate of approximately 150 gal/min. The pipe coming off each valve, one at the bottom of each reservoir, will be 4" diameter.

Is there a manifold/header that enables the liquid to be suctioned (by the pump), at the same flow rate at each manifold/header entry point??
Is there a simple way of doing this??
I was going to have a pipe come down from each reservoir to a common header, which is capped at one end, with the pump on the other end. However, the flow rate from the reservoir closest to the pump will be the greatest, followed by the next closest etc...
I do not really want to put any flow regulators/restrictors on the suction side of the pump if possible...

Can anyone help me out with this???
Greatly appreciated...

Regards,
Jack M

 

[btrueblood]

Do you mainly just want the liquid in the tank to "run dry" at about the same time? Then just plumb it like you said. If one tank gets drawn down preferentially, it will eventually reach a point where the gravity head difference between its level and the other tanks will cause the higher tanks to flow more. At 4" of pipe diameter, there won't be much head difference at equilibrium. And, if the pumping is intermittent, the tanks will equalize to the same level every time the pump stops.

Ben T.

 

[MikeHalloran]

Suppose I sold you a 'magic header' that would 'guarantee' the 'same flow' from all reservoirs, exactly as you desire? It would, of course, cost an obscene amount of money, because magic isn't cheap.

Suppose that it didn't actually work?

How would you KNOW? How would you PROVE it?

You need to specify a tolerance on 'same', and a temporal measurement interval, in order to complete your specification.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[MortenA]

Make the piping fairly symetrical and the point about difference in head should take care of the rest.

Maybe you could include a "manual control valve" on each suction line that you could tweak a little if experience tells you that one tank empties faster then the others.

Best regards Morten

 

[25362]

To jackieboy, would you kindly explain:

1. The reasons for the need of the three reservoirs dropping their levels equally and simultaneously.

2. Whether the solutions at the same temperature and with equal viscosities and densities ?

3. Whether the solutions tend to produce precipitates ?

If the answers

to item 1. is none;
to item 2. is yes;
to item 3. is no.

the posts by btrueblood and MortenA are both OK.

Otherwise, appropriate clarifications are needed.

 

[jackieboy]

Hey Guys...

I should have given more details on my project.
The reservoirs will never run dry.
I will be pumping the solution through a filtration tank, and then using valving and piping I will be delivering the solution back to each reservoir at approximately 150 gal/min.
Therefore, I need to pump 150 gal/min from each reservoir (suction side of pump), and I will be delivering the solution back into each reservoir at 150 gal/min, after the solution is filtered.
The solution in each reservoir is at the same temp, density, and viscosity. I didn't really want to put in manual control valves on the suction side of the pump if possible. These valves would need to be tweaked, and putting resistance on the suction side is not a very good idea I don't think?? Am I right??
When I say the "SAME" flowrate, I mean approximately an equal flowrate from each reservoir, lets say 150 gal/min +/- 10 gal/min is fine. It doesn't have to be exact.

The current system in place uses a common header, with a pipe coming in from each reservoir. However the flowrates are not even close to being the same. One flowrate is at 50 gal/min, whereas the flowrate in the one pipe closest to the pump (going into the header) is at 170 gal/min.
I need to replace this with a system that is more equalized, with more balanced flowrates .

Any suggestions would be greatly appreciated...

Regards,
Jack M

 

[btrueblood]

Jack,

How did you measure the flow rates?

50 gpm in a 4" line is pretty slow. 170 gpm is getting a little higher, but still slow. I think Morten's idea of sticking a manual valve in each line and balancing flow that way is a good one in this case. You may end up with slightly lower pump suction pressure (or higher vacuum, whichever way you want to look at it), but as long as the NPSH is high enough for your pump, who cares.

Lastly, have you seen the tank level get way out of whack when the system is running? Letting the reservoirs balance out by having a different head/level on each is the simplest way to go (and this engineer LIKES simple)...

 

[BenThayer]

how are you measuring the flow out of the individual tanks?

unless i am missing something, your distribution problem is being caused by poor return flow distribution back to your tanks.

the three tanks are balanced at the suction and so balance between the tanks will keep the levels the same, assuming reasonable sized suction piping.

if you are indeed pulling more flow from one tank, you must be returning more flow to that tank. do not throttle the suction side of the pumps!