Size expansion vessel to reduce pressure loss

In summary, the pressure vessel is filled with water at 8 bar pressure and has a valve and expansion vessel installed on top. When the valve is opened, 20 liters of water is lost, resulting in a pressure loss in the vessel. Without an expansion vessel, the new pressure will be zero once all the vapor is vented. With an expansion vessel, the new pressure will be a function of the draining liquid's pressure head. The pressure will continue to decrease until it reaches the backpressure at the discharge point, the vaporization pressure of the liquid, or the buckling strength of the vessel. The rigidity of the tank also plays a role in the pressure loss.
  • #1
RobinDeG
Hi all,

Given:
I have a pressure vessel of 1000M^3 filled with water with 8 bar pressure.
On this pressure vessel I have installed a valve and a expansion vessel on top of the pressure vessel.
The expansion vessel is prepressurized to 8 bar as well.

Question:
when I open the valve i lose 20 liters of water.
The decrease of water will result in a pressureloss in the vessel.

Question 1: what will the new pressure be (without an expansion vessel)
Question 2: What will the new pressure be with an expansion vessel

To make it easier: the expansion vessel will be filled with water also.
 

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  • #2
If both vessels are liquid full then the pressure measured at the level of the outlet will be the combination of the 8 bar imposed pressure plus pressure head of the contained liquid. lf all vapor has been vented from the expansion vessel and the liquid is essentially incompressible then the 8 bar of imposed pressure will quickly drop to zero (the actual time will depend upon the vessel material's modulus of elasticity and pressure stress on the vessel).

If there is a vacuum breaker attached to the top of the expansion vessel, the pressure measured at the outlet level will then be a function of the pressure head of the draining liquid until the vessel is emptied to the outlet level.

If there is no vacuum breaker on the expansion chamber, once the initial 8 bar pressure reaches zero, the draining liquid will begin to develop a vacuum in the vessels' volume above the liquid level that is proportional to the increase in that volume. This vacuum will continue to increase until: 1) the vacuum is equal to the backpressure at the vessel's discharge point (assuming no air is drawn into the vessel through the draining discharge connection) or: 2) the vacuum reaches the vaporization pressure the liquid in the vessel; or, 3) at some point, the vacuum exceeds the buckling strength of the vessel and the vessel collapses.
 
  • #3
How rigid is the tank? 20L is quite a small percentage of 1,000,000L.
 

Related to Size expansion vessel to reduce pressure loss

1. What is a size expansion vessel?

An expansion vessel is a type of tank used in HVAC systems to control the pressure within the system. It is designed to absorb excess water volume and maintain a constant pressure, preventing pressure fluctuations and system damage.

2. Why is it important to have a properly sized expansion vessel?

A properly sized expansion vessel helps to reduce pressure loss in the system. If the vessel is too small, it will not be able to accommodate the excess water volume and pressure will build up, potentially causing damage. If the vessel is too large, it can lead to pressure drops and decreased system efficiency.

3. How do I determine the correct size expansion vessel for my system?

The size of the expansion vessel depends on the total volume of water in the system and the maximum pressure it can reach. A rule of thumb is to select a vessel that can hold 10% of the total system volume and has a maximum pressure rating of 1.5 times the system pressure. However, it is best to consult a professional to determine the exact size needed for your specific system.

4. Can I use multiple smaller expansion vessels instead of one large one?

While it may seem like using multiple smaller vessels would work, it is not recommended. Having multiple vessels can create imbalances and uneven pressure distribution within the system. It is best to use one properly sized vessel for optimal performance.

5. How often does the expansion vessel need to be replaced?

The lifespan of an expansion vessel depends on various factors such as usage, water quality, and maintenance. On average, an expansion vessel can last anywhere from 5 to 10 years. It is important to regularly check the vessel for any signs of damage or wear and replace it when necessary to ensure proper functioning of the system.

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