Generally it is recommended to keep the expansion tank (deaerator tank) at a certain height (say 6-9 feet) above the pipe line. What is the concept behind this?
The two main reasons are the following ones:
Facilitate de degassing of the fluid since the gas bubbles tend to rise and to get captured in the expansion tank.
Have the tank working at a lower pressure because to the pressure in the expansion tank you must add the pressure head between the tank and the pipe line. Keeping a lower pressure in the tank makes less critical its sealing problems.
The two main reasons are the following ones:
Facilitate de degassing of the fluid since the gas bubbles tend to rise and to get captured in the expansion tank.
Have the tank working at a lower pressure because to the pressure in the expansion tank you must add the pressure head between the tank and the pipe line. Keeping a lower pressure in the tank makes less critical its sealing problems.
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Only complementing accurate informations Giovanni.
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Have the tank working at the lower pressure reduces the need for thicker walls, it is more economical.
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The height can ensure a predetermined pressure given by the column of liquid in the pipe, in the power plants located deaerator a height which ensures the suction pressure of the booster pump group of boiler feed water pump.
If you don't create a pressure balance between the main line and the open surface of the liquid in the expension tank, the liquid will escape the line through the expansion tank. that is, I think the number one reason.
Mr. Taherian, pay attention that sometimes the fluid in the expension tank is not at atmospheric pressure since a membrane, pushed by a gas, may exist. So, in principle you could locate the tank everywhere in the circuit.
@ Giovanni: Yes you are right. I should have mentioned in my answer that I was talking about atmospheric expansion tanks only. Thanks for clarification.
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Dear friends.
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Perhaps the question has led some to error. How was formulated (and I think this was not the intention of Taherian) "Why the expansion tank (tank deaerator)", it seems that the terms expansion tank and deaerator tank are synonymous, and in fact are not. Trying to interpret the question Taherian he wanted to know about an expansion tank WITH an air valve (making it an "expansion tank" with one desaerator).
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The configuration in the expansion tank with deaerator is very common, but not required. The primary function of the expansion tank is to minimize water hammer or stabilize flows suffering the influence of flow variations over time.
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When the input fluid is taken from the top of the tank the presence of the air valve is not required, this valve can be placed elsewhere in the circuit (higher portions of the duct). In the case of bottom liquid inlet or other characteristics of the hydraulic circuit of an air valve placement is required.
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From what he's writing is Taherian sizing a expansion tank and some need the tank or characteristics of the circuit design he sees fit to the placement of a combination of expansion tank with an air valve (very convenient situation because it puts the inspection of two structures a single point mechanical facilitating maintenance).
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Warning, do not have an attorney of Taherian to interpret their texts, I'm just trying to avoid problems due to errors of interpretation.
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It also acts as a surge tank , taking out any surge in pressure and smoothen the flow as ell
These tanks have tow duties. As for deaeration, since the buoyancy force pushes the fluid bubbles (i.e. air) to rise up toward higher heights, the tank should be placed upper than the highest place of the pipeline to make sure no fluid bubbles remain in the pipeline.
Continuing Hossein's comment: To make sure also that the bubbles will not return to the working pipe from the tank..
I think we are wasting our time since I believe that the guy who asked the question (like other ones he asked) is trying to have his home work done by other people.
You are very right Carlomagno, either they are lazy or not willing to read on their own
Giovanni and Mohamad.
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We could classify the author of this question as a compulsive questioner, only this year (16 days) it has 22 questions!
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sThanks Rogerio for giving the statistics. While we were wasting our time in giving more accurate answers, he did not participate to the discussion at all. This made me suspicious. By the way, should you have the chance, please greet for me the former rector of your university prof. Francisco Ferraz, who I frequented about 46 years ago while I was staying in Princeton University.
Thanks a lot to all for the valuable inputs - I am very sorry that I have not responded to your inputs
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