2 replies to this topic

[ayan_dg]

Is the size of the overflow nozzle be same as the inlet nozzle of the tank ? What is the guideline in designing the size of overflow nozzle of an atmospheric storage tank

[JoeWong]

Is the size of the overflow nozzle be same as the inlet nozzle of the tank ? What is the guideline in designing the size of overflow nozzle of an atmospheric storage tank

Rule of thumb, 1 or 2 size bigger to ensure positive flow...

[Art Montemayor]

Ayan:

It is important that you should understand that an atmospheric tank is NOT DESIGNED to withstand any sort of reasonable pressure. It is a very weak vessel and is only intended to store liquids at essentially atmospheric pressure - seldom over 3.5 psig of pressure.

Therefore, it is very important that you realize that it is IMPERATIVE that you not allow the tank to fill 100% with liquid while it is filling with an outside, pressurized source. The tank would surely rip apart if it had no "safety" oveflow for its liquid to the atmospheric ambient. Your concern is well taken and I would advise you to take careful steps to ensure that your overflow device works successfully every time it is needed. The weakest point of a fixed roof atmospheric tank is the joint between the cone roof and the cylindrical wall. This joint will be the first place to fail structurally if the tank is over-pressured by gas or by liquid. Once the conical roof joint fails, the cylindrical shell deforms immediately and the tank basically collapses, spilling all its contents. Human lives can easily be jeopardized under this type of credible scenario. For any liquid "overflow" to work successfully, it must be SELF-VENTING. Here, I am assuming the overflow is by gravity and to the surrounding grade around the tank. Without self-venting, the liquid discharge (or overflow) will sputter and not drain efficiently. This will reduce its capacity and the tank will be in danger of over-filling. This fact is often overlooked by many engineers and is a fact that has been borne out many times. This is an action that can be witnessed by your sink drain at home. If the drain pipe is not vented to the atmosphere, the drain will not function correctly and will back up.

Draining by gravity is a simple, but special flow of fluids that should be clearly understood because although it looks rather simple, it can cause a serious engineering error. A famous article by an author named Hills is often referenced when dealing with gravity flow. I have included this article in my workbook, "Fluid FLow", which I have posted in a past thread. Irecommend that you should familiarize yourself with gravity flow in order to design this overflow device.