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# Determining Operating Pressure In Pressure Vessel

water pressure vessel pressure operating pressure vessel lcv level control

3 replies to this topic
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### #1 inkar

inkar

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Posted 01 October 2022 - 01:39 AM

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Edited by inkar, 12 October 2022 - 02:29 AM.

### #2 Pilesar

Pilesar

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Posted 01 October 2022 - 07:21 AM

Your diagram is a simplified description of what would be in the field. The items missing must be deduced or assumed. For example, the water pressure vessel has one inlet and no outlet for vapor or liquid shown. Actually, it likely has outlet for liquid and also an outlet for any vapor and also a way to control pressure and liquid level. Deducing from what is shown, the pressure of the water pressure vessel will be 15 psig. The missing pressure controller for the water pressure vessel is just not shown.

### #3 Pilesar

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Posted 02 October 2022 - 02:04 PM

You ask more speculative questions. You can keep adding details that go beyond the initial diagram as you wish. I am not complaining, but seek the reason for the questions. Is there a real scholastic problem you are trying to solve or is this just something you imagined? I suggest you review the Bernoulli equation regarding pressure drop. Your initial diagram showed 15 psig after the liquid control valve. So that is the pressure. The water pressure vessel does not have to be at 15 psig pressure but it could be. In the absence of any other pressure measurement or control, it is a reasonable assumption based on the diagram. The water pressure vessel could be higher or lower pressure than 15 psig -- nothing is given about elevation changes! The diagram suggests the water pressure vessel is lower than the control valve so it might cancel the pressure drop due to friction in the piping. If you want to calculate exactly the pressure at a particular point in the water pressure vessel, then you would need more information. Since the information is missing, why not assume the 15 psig applies to the water pressure vessel also? You added a pressure controller on the water pressure vessel. Pressure controllers really need a compressible fluid for control. Small changes in liquid inventory can change pressure drastically in a full vessel with no vapor space and cannot easily be controlled to a setpoint. So if pressure were to be controlled, the vessel would have a vapor space with controls on the vapor inventory to adjust pressure. Alternatively, the vessel might keep liquid full using flexible walls such as a rubber bladder to keep pressure nearly constant while adjusting vessel volume with the liquid inventory.

### #4 Pilesar

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Posted 02 October 2022 - 08:59 PM

I think you would appreciate playing 'what if' with a simulation package that does fluid flow calcs. There is much that is not necessarily intuitive when evaluating pressure drops. Especially when the fluid is two phases. I've enjoyed our discussion and wish you success in your studies. Here is a speculative question for you to consider. What if the liquid entered the water pressure vessel through an internal dip pipe with no vent? How would that affect the vessel pressure given your same assumptions? https://postimg.cc/JHr08Bf5