equalizing two storage tanks
equalizing two storage tanks
(OP)
Hi,
I have a 135' dia steel water tank that is inside a concrete basin. If something happened and somebody let the sludge lines open in the 135' tank, and that tank started to drain, I need to be able to take water from the outside tank to the inside tank. I need to be able to keep the two tank equalized. My inner tank will withstand up the 3.81" of water column. Does anybody have any ideas on how to make this possible.
thanks
danny
I have a 135' dia steel water tank that is inside a concrete basin. If something happened and somebody let the sludge lines open in the 135' tank, and that tank started to drain, I need to be able to take water from the outside tank to the inside tank. I need to be able to keep the two tank equalized. My inner tank will withstand up the 3.81" of water column. Does anybody have any ideas on how to make this possible.
thanks
danny






RE: equalizing two storage tanks
you have a tank within an outer containment wall (the outer tank?)
initally you have the inner tank full and the outer tank empty.
then you start to empty the inner tank into the outer one.
then, whilst this transfer is happening, you want to transfer from the outer to the inner? (to restore the inital condition?)
but then you say "I need to be able to keep the two tank equalized." ?? if the two tanks were equalised then there'd be no flow between them, no?
Quando Omni Flunkus Moritati
RE: equalizing two storage tanks
thanks
danny
RE: equalizing two storage tanks
Quando Omni Flunkus Moritati
RE: equalizing two storage tanks
RE: equalizing two storage tanks
RE: equalizing two storage tanks
Just brainstorming as I have no experience relating to this... create an expanding diaphragm inside of the inner tank connected to the outer tank, such that, if pressure is higher on the outside tank, fluid would flow into the diaphragm equalizing the pressure.
I would think making it impossible to evacuate one tank without evacuating the other would be the best option. What mechanisms would allow the tanks to drain? Just valves? Can you put pressure sensors in place in each of the tanks and implement an electronic controller which would open or close the required valves if the critical pressure differences were approached?
RE: equalizing two storage tanks
RE: equalizing two storage tanks
RE: equalizing two storage tanks
RE: equalizing two storage tanks
RE: equalizing two storage tanks
but i'm confused about the problem. if the two tanks are equalised and someone opens a valve between them, there won't be any flow, no? if theyn't equalised then they'll flow towards an equalised state, no?? or is the outer tank draining to the outside world, so you have inequality between the inner and outer tanks.
i can see the question arising when you're filling the tanks, ie filling one of them.
Quando Omni Flunkus Moritati
RE: equalizing two storage tanks
RE: equalizing two storage tanks
the inner tank is filled either from the ground or from a pipe above, when the process is done it flows the basin or outer tank. The outer tank then flow out into the "world" If someone left the sludge line on the inner tank on the tank will then unfill, after 3.81" of wc difference my inner tank would collapse. What we are wanting is like a emergency method to get water back into the inner tank to hold 3.81"-. This way we know the inner tank will not fall down. A valve, pipe configuration, or something to keep this from happening
thanks
danny
RE: equalizing two storage tanks
what type of 24" valve did you try? check valve?
RE: equalizing two storage tanks
Wouldn’t a couple 6-8" dia. steel pipes (you determine how many and pipe dia.), in a “U” shape with two vert. legs, with a 180̊ elbow at the top, and 4' vert. legs on one, and 6' vert. leg on the other (several different depths in the tanks) act as siphons once they were filled. You hang these siphons over the wall btwn. the two tanks, have some means of filling them, and some means (a sight glass or some such) to check that they are staying full. Alternatively, a small pump from the cleaner tank would keep them full, once they were filled. Any way the siphon can be broken is the issue here, air leakage, etc.
RE: equalizing two storage tanks
they said it cannot hold the 3.81" of w.c. that is could fall in the range of 4-7"
thanks
RE: equalizing two storage tanks
i think the point the manufacturers have is that pipe losses depend on things outside their control.
i'd design a piping that has twice the capacity of the accidentally opened outflows, so i'd ne reasonably confident that i'd have the flow. Next i'd need a control system to sense the difference in level between the tanks and react.
Quando Omni Flunkus Moritati
RE: equalizing two storage tanks
RE: equalizing two storage tanks
RE: equalizing two storage tanks
Quando Omni Flunkus Moritati
RE: equalizing two storage tanks
RE: equalizing two storage tanks
For emergency vents on petroleum tanks, they use a large opening with a lightweight cover that can lift under pressure, but restrained by long bolts. For that kind of a situation, you are allowed to calculate theoretical flow through the orifice and apply a coefficient of 0.5; that is you treat it like just a hole and then design for the half the flow capacity that gives you. That would seem to be a reasonable way to design with the flap valves. The differential pressure has to be enough to open the valve, of course. Use Bernoulli's equation between the two tanks, account for minor losses due to re-entrant flow and abrupt exit, etc.
Also keep in mind that flap valves are often used in applications where there can be no backflow anyway. It's possible they won't be overly effective at sealing in the reverse direction if that's an issue.
For external pressure on a steel cylinder, there is some variation in the factors of safety that are used, and you may be able to juggle your numbers some due to that.
RE: equalizing two storage tanks
The problem is the lack of head. At maximum we have 3.81 inches of water, about 19 lbs/sqft! at the bottom of the pressure triangle, average pressure of about 9 lbs/sqft. That will not move a lot of water very quickly.
I have a difficult time with the idea that more than 4" differential will bring a tank down. If it were there for the whole height, maybe, but in with the limited height, the load will spread over a considerable distance above the top of the fluid.
Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin
RE: equalizing two storage tanks
RE: equalizing two storage tanks
What is the normal liquid height difference between inner and outer?
What size pipe / valve does it normally flow through?
what is the normal liquid flow rate out from the inner tank?
What is the flow rate out from the sludge lines?
3.81" looks suspiciously like 10mbar to me. As said earlier - this is a very low differential pressure, both for tank collapse or to make it flow. Who gave you this limit?
So IMO, you can either
a) Strengthen your tank to resist greater differential pressure
b) Do some more structural calcs to see if this differential (3.81") acting on only part of the tank (we have no info on height of the relevant liquid levels) actually causes collapse or not
c) Make about 50% of the tank area at the base slots to allow flow in (again we have no idea about flow rate going out through the "sludge lines")
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: equalizing two storage tanks
RE: equalizing two storage tanks
RE: equalizing two storage tanks
JStephen, I wasn't thinking straight.
Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin
RE: equalizing two storage tanks
I’m glad you finally mentioned siphons, or they got mentioned again. Take a look back at my 4FEB14, 15:26 post. The OP’er. was too busy tweeting, at that point in time, to actually read his own thread very carefully. I thought it would at least generate a comment or some discussion, but I guess not, until now, maybe. I figured, screw it, if they are too busy playing with themselves, and can’t take the time to read more than two sentences for content, maybe they don’t need that idea.
RE: equalizing two storage tanks
RE: equalizing two storage tanks
if you knew a max height for the inner tank you could provide a fluid path a little below this. But it sounds more like a relative height difference? that's why i thought of a float valve ... floats on both tanks, open a valve if difference greater than X(<3.8)
Quando Omni Flunkus Moritati
RE: equalizing two storage tanks