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equalizing two storage tanks

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

RE: equalizing two storage tanks

i read your question as this ...

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

(OP)
both tank have water at all times, the inner tank either gets its water from the ground or from a pipe above, it flows into the outer tank. if the operator left the sludge lines open, the inner tank would begin to drain. it can structurally hold 3.81" of water col (inner to outer) we need a way to hold at the most 3.81" of wc, we need to do this by water going into the inner tank from the outer tank. This will equalize the tanks, what is the best way to do or figure this.


thanks

danny

RE: equalizing two storage tanks

you meant like a float valve ?

Quando Omni Flunkus Moritati

RE: equalizing two storage tanks

(OP)
will a float valve allow water to flow from the outer tank to the inner tank

RE: equalizing two storage tanks

I guess you want to maintain the original water levels within the inner and outer tanks at all times, assuming that the inner tank water level is always higher than that of the outer tank. Unless you have a pump with the proper controls for the inside and outer tank, I don't know how you could maintain both water levels in the event that the inner tank sludge line was opened. The pump flow rate should be equal to or greater than the expected maximum flow rate thru the open piping.

RE: equalizing two storage tanks

I assume that it is not acceptable for the fluid in the inner tank to mix with the fluid in the outer tank?

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

(OP)
we have looked at several valves, but nobody can tell us the flow rate, we want to use one of those flap valves but the manufacture will not give us the information.

RE: equalizing two storage tanks

Is it acceptable for the water from the outer tank to enter the inner sludge tank?

RE: equalizing two storage tanks

(OP)
yes

RE: equalizing two storage tanks

Why not just use check valves (one way flow) with adequate flow? They would automatically close unless the pressure in the sludge tank was less than the pressure in the water tank.

RE: equalizing two storage tanks

the flow between the tanks is governed by the pressure you supply .. and by the Cd of the valve, sure. if they won't give you flow rates (odd that, no?) then assume something for design purposes and test it.

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

(OP)
we tried this I went to tideflex and purchased a 24" valve but it will only get us are 5-7" w.c. Every manufacture we call says an engineer has to verify flow, we need 2800gpm, but our structural engineers cannot figure this one out..

RE: equalizing two storage tanks

(OP)
rb1957 (Aerospace)

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

not sure what "it will only get us are" was supposed to mean?

what type of 24" valve did you try? check valve?

RE: equalizing two storage tanks

Custom2014:
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

(OP)
24" checkmate valve,

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

"our structural engineers cannot figure this one out" ... i think maybe you need better engineers ... smile!

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

you can't vent the tank to prevent collapse?

RE: equalizing two storage tanks

(OP)
what do mean by venting??????????????

RE: equalizing two storage tanks

i think it's a tank like a swimming pool ... open at the top.

Quando Omni Flunkus Moritati

RE: equalizing two storage tanks

(OP)
yes it is

RE: equalizing two storage tanks

I have seen flow data for Waterman flap valves, but it is based on discharging into atmosphere. Normally, a flap valve is used in applications where it has minimal effect on flow, and so flow data is not that readily available.

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

I don't know what structural engineers are supposed to work out on fluid flow through a valve.

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

The differential between inner and outer pressures will be applied through the whole depth of the lower fluid, not just at the top. The design wind pressure for tanks is typically around 18 psf, although it doesn't control the design that often. But that pressure rating is a reasonable figure.

RE: equalizing two storage tanks

A simple cross section sketch with heights, normal liquid levels etc would help, but from what I've read so far you have a thin inner metal tank with normal flow from inner tank to outer "bund". You then have an upset condition where levels in the inner tank could be less than the outer tank and you are worried about collapse of the steel tank.

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

Structurally, Where do you need help in this "Structural engineering other technical topics" Unless I missed something, isnt this a mechanical engineering problem?

RE: equalizing two storage tanks

This thread makes no sense. 3.81" wc (inches water column) sounds like it could be a vacuum limitation on a closed tank of that size, but this is an open tank. That much water standing outside of the tank could not possibly damage it. 3.81 feet might be a problem. The simplest solutions to that issue would be to place braces inside the tank to support the walls, like an inside-out above ground pool.

RE: equalizing two storage tanks

The solution might be to place siphons over the inner wall so that the ends are near the bottom of the tanks. They would have to be primed. Don't know how to size them though.

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

Paddington:
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

I don't see how putting primed siphons over the wall would be any different from just putting an open hole in the way, free flow either way?

RE: equalizing two storage tanks

that's what i was thinking about ... fill both tanks at the same time, have a direct fliud path between them ... poses the question , why two 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

What is the specific gravity of the sludge?

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