hydraulics puzzle - Router Forums
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post #1 of 30 (permalink) Old 08-11-2018, 03:16 AM Thread Starter
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Default hydraulics puzzle

heres a puzzle for you lot.
First, the background;
2 water storage tanks, side by side.
Both have ball valves on the inlets.
1 tank is taller than the other.
Both outlets are joined into one pipe to the pump for pressurising the system.
The lower tank has a check valve fitted to stop the taller tank over flowing the lower tank.

Now the puzzle;
When water is drawn off, only the taller tank flows. The lower tank does not flow any water at all.

What needs to done / fitted, to make both tanks flow equally?
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post #2 of 30 (permalink) Old 08-11-2018, 06:59 AM
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Assuming the tall tank fills first and then the shorter on fills from it. Seems to me that both tanks should flow equally when water is drawn by the pressure pump. Ie. They both should empty at the same rate.
Fill both tanks and isolate the taller tank. See if the pressure pump draws water. Should be able to eliminate the taller tank's out flow line to the common line and, draw only from the lower tank with the taller tank flowing into the lower one as needed.

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post #3 of 30 (permalink) Old 08-11-2018, 07:40 AM
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I'm no plumber but.....all check valves I've seen and used were designed to allow water to flow in one direction......won't allow a backflow. Now I could see a solenoid valve being installed on the taller tank with a float switch installed on the lower tank activating the valve to close when water reaches the desired level on the lower tank but that's an old HVAC controls guys thought.

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post #4 of 30 (permalink) Old 08-11-2018, 09:32 AM
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If you could raise the smaller tank until it's level at the top with the larger tank and eliminate the check valve the smaller tank can empty into the larger one and the pump will pump from the large one. I suspect what you may have is a pipe going to the larger tank with the smaller tank teed into that pipe. When the pump goes it draws water past the tee and literally forms a water pressure wall at the opening to the small tank. If that's the case then the solution is to change the plumbing to a Y type setup where the outlet from each tank feeds into an elbow into a common pipe with a tee in the middle that goes to the pump. That arrangement should feed equally from both tanks- to a point as the larger tank will have higher head pressure until they equalize.
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post #5 of 30 (permalink) Old 08-11-2018, 10:57 AM
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I'm with Steve on this. I'm trying to understand how the check valve solves anything(?). if the larger tank is in fact taller, than when it's filled the outflow pressure is higher than the shorter tank without any pressurization simply by reason of physics (head).
I would have connected the two tanks lower down with a fill pipe to only one, and an outflow pipe from only one, the other tank.
If the tanks are pressurized (sealed), how can they "overflow"?

What Charles said about the tanks equalizing!
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post #6 of 30 (permalink) Old 08-11-2018, 11:43 AM
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I think it is more like Chuck says,the pressure from the upper tank is keeping the check valve closed until the upper tank is empty to the point of being level with the lower tank the check valve will not open to allow the lower tank to flow. I don't think the "Y" instead of a "T" will still allow the water to flow because the pressure is greater from the taller tank, until it is partially empty and as long as the pressure when the faucet is opened does not reduce the pressure to the point of being greater than the upper tank, the check valve will not open.

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post #7 of 30 (permalink) Old 08-11-2018, 01:05 PM Thread Starter
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I cant adjust the heights of the tanks. the lower one is a 1000 litres, the taller one is 750 litres (think 2 oil drums, one laying down, one standing up).
They are connected in parallel, mains to both ball valves (NOT pressurised tanks). Both bottom feeds are connected via a T. The taller tank is on the T, the lower tank has a straight line to the pump.
The check valve is to stop the two trying to equalise levels via the bottom feed pipe. The lower one would overflow.

I think youre right in that even when the pump is scavenging water from the tanks, there must be enough back pressure from the higher tanks increased head stopping the lower tank emptying.

Short of a motorised valve, i dont think I have any option but to manually shut off the tall tank every few days to stop the lower tank going stagnant.
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Last edited by sunnybob; 08-11-2018 at 01:08 PM.
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post #8 of 30 (permalink) Old 08-11-2018, 02:00 PM
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Quote:
Originally Posted by sunnybob View Post
I cant adjust the heights of the tanks. the lower one is a 1000 litres, the taller one is 750 litres (think 2 oil drums, one laying down, one standing up).
They are connected in parallel, mains to both ball valves (NOT pressurised tanks). Both bottom feeds are connected via a T. The taller tank is on the T, the lower tank has a straight line to the pump.
The check valve is to stop the two trying to equalise levels via the bottom feed pipe. The lower one would overflow.

I think youre right in that even when the pump is scavenging water from the tanks, there must be enough back pressure from the higher tanks increased head stopping the lower tank emptying.

Short of a motorised valve, i dont think I have any option but to manually shut off the tall tank every few days to stop the lower tank going stagnant.
So how do you fill the 2 tanks? Can the lower tank be sealed so that the upper tank fills it? then the drain could be straight from the lower tank.
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post #9 of 30 (permalink) Old 08-11-2018, 02:25 PM
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Quote:
Originally Posted by Herb Stoops View Post
So how do you fill the 2 tanks? Can the lower tank be sealed so that the upper tank fills it? then the drain could be straight from the lower tank.
Herb
That's what I was trying to say. But, you said it more better.

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post #10 of 30 (permalink) Old 08-11-2018, 02:29 PM
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I've come across a few situations like this Bob when I was hauling potable water and filling multiple tanks (with valves on the infill lines as well) and the solution was to partially close the valve(s) on the tank(s) that filled first. The same would hold true on the outlet valves. Over time you'll find the valve position that works.

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