The function of the intermediate connecting cylinder between the gas side and the water side of the level gauge in a single-chamber equilibrium vessel

Please check whether the illustration matches the actual situation.

Bro, looking at the connecting cylinder, it serves no purpose at all for differential pressure measurement. I guess the cylinder is there as a placeholder for some kind of level gauge. . . This broken tube is not only useless but also harmful to the differential pressure gauge. Due to the rupture tube, which functions as a buffer damper, when the gas phase pressure in the large tank increases rapidly, the rate of pressure increase within the rupture tube lags behind that in the large tank; as a result, the reading on the differential pressure gauge becomes higher. Similarly, when the pressure in the large tank decreases rapidly, the rupture tube causes the reading on the differential pressure gauge to be lower. Essentially, within the broken tube, the imbalance in the rates of change between the liquid-phase pressure and the gas-phase pressure ultimately leads to oscillations in the differential pressure measurement, that is, to jumping fluctuations.

It’s consistent, although the drawing isn’t particularly good. The container is equipped with differential pressure level gauges that consist of multiple single-chamber balance containers. Some of these gauges lack the connecting cylinder labeled 2, while others have this connecting cylinder. Those without the connecting cylinder labeled 2 are used for water level control and alarm functions; those without an intermediate connecting cylinder are used solely for reading purposes and do not participate in any logical control processes

I’ve learned something! In reality, when there is a sudden change in pressure, some level gauges with an intermediate cylinder do experience significant fluctuations, while those without such a cylinder remain relatively stable. I’ve seen on the internet that without an intermediate cylinder, measurements may be unstable, as the negative pressure does not result in a stable density for steam and water. In the papers I’ve seen online, those without an intermediate cylinder are generally described; it’s rare to see mentions of those with an intermediate cylinder. Have they been phased out?

I’ve learned something! In reality, when there is a sudden change in pressure, some level gauges with an intermediate cylinder do experience significant fluctuations, while those without such a cylinder remain relatively stable. I’ve seen on the internet that without an intermediate cylinder, measurements may be unstable, as the negative pressure does not result in a stable density for steam and water. In the papers I’ve seen online, those without an intermediate cylinder are generally described; it’s rare to see mentions of those with an intermediate cylinder. Have they been phased out?

It has been basically phased out; a single-chamber equilibrium vessel with pressure and temperature compensation is more effective

I feel that part 2 is unnecessary; it can be removed.

Standard DL/T 1393-2014, \"Technical Specifications for the Water Level Measurement Systems of Boilers in Thermal Power Plants,\" specifies the use of a single-chamber balance vessel for measuring boiler water level; this standard is provided in the attachment. Differential pressure level gauges all require a balance vessel, but some users are not very familiar with it, especially when it comes to understanding the internal structure of the double-chamber balance vessel, which affects its proper use. Changhui Instrument Manufacturing Co., Ltd. shares with you knowledge related to balance vessels. A differential pressure level gauge operates on the principle of hydrostatic pressure balance; the balancing container functions as a \"level–differential pressure\" converter. Its function is to generate a constant hydrostatic pressure, which is then compared with the hydrostatic pressure resulting from the liquid level being measured, so as to output the difference between the two. A balance vessel is essentially a condenser, and based on its structure, it can be divided into single-chamber balance vessels (single layer) and double-chamber balance vessels (double layer). The structure of balance vessels for large boilers is more complex; here, only the FP-type balance vessels commonly used in industrial boilers will be introduced. http://yunrun.com.cn/upload/201607/19/201607191649375791.jpg Balanced container. yunrun.com.cn/tech/962.html The structure of a single-chamber balanced container is relatively simple, as shown in the figure. When measuring the liquid level in low-pressure vessels, when there is a large temperature difference between the inside and outside of the vessel, or when the gas phase tends to condense into a liquid – such as in the case of the water level in deaeration tanks – single-chamber equilibrium vessels are generally used for measurement. Before measurement, the plug of the balance vessel should be removed according to the properties of the medium being measured, and cold water or another liquid should be poured in. In some toxic and hazardous environments in chemical manufacturing, isolating fluid is filled in the balance vessels. http://yunrun.com.cn/upload/201607/19/201607191650137978.jpg The structure of the two-chamber equilibrium vessel is shown in the figure. A dual-chamber balance vessel is used to measure the water level in the boiler drum; this balance vessel consists of an inner and an outer chamber. The outer chamber of the balancer is connected to the steam in the boiler drum and is filled with condensed water ； The inner chamber is connected to the water in the boiler drum through a pressure guide tube located below the balancer; the principle of a communicating vessel is applied here, so the water level in the inner chamber changes in accordance with the water level in the drum. The double-layer container of this design ensures that the water temperature in the outer chamber and the inner chamber is essentially the same, thereby reducing measurement errors caused by temperature differences. The boiler water level is measured using a two-chamber balance vessel; the outer chamber of this balance vessel is connected to the steam in the boiler’s drum, and this outer chamber is filled with condensed water ； When the water level in the outer chamber is below the pressure guide tube at the upper end of the balancer, it is replenished by the condensate water from the boiler drum; when the water level is above that pressure guide tube, water flows into the boiler drum through the guide tube, thereby keeping the water level in the outer chamber constant. The inner chamber is connected to the water in the boiler drum through a pressure guide pipe located below the balancer, and its water level changes in accordance with the water level of the drum. If the pressure and temperature parameters of the steam remain constant, the output signal of the differential pressure transmitter is dependent only on the water level in the boiler drum. For low-pressure boilers, since the density of the water in the inner vessel is approximately equal to the density of water at the saturation temperature, the height of the water column in the inner vessel of the dual-chamber equilibrium vessel is equal to the actual water level height in the drum. Since the outer chamber of the balancer is connected to the low-pressure side of the differential pressure transmitter, the inner chamber is connected to the high-pressure side of the differential pressure transmitter. At this point, the pressure difference generated between H and L is △P = Lρl- ； Since ρ1=ρ2, therefore △P = Lρ1 – Hρ1 – (L–H)ρQ = (L–H)(ρ1–ρQ); this formula represents the conversion relationship between water level and differential pressure. In other words, when using a two-chamber balance container to measure the water level, its working principle relies on the principle of hydrostatic pressure; it converts the mass of water in the steam drum into a differential pressure, which is then converted by a differential pressure transmitter into an electrical signal that is sent to the display and control instruments or the DCS system. It should be noted that, for the sake of easier understanding of the problem, the differential pressure △P in the above examples refers to the height of a water column; in practical applications, it needs to be converted into Pa, by simply multiplying it by the local gravitational acceleration g, that is, △P = g. For many medium and small industrial boilers, since the pressure of their saturated steam is not high, they are generally treated using ρ1=ρQ; in this case, the differential pressure corresponds to the height of the water level in the inner chamber, that is, △P=ρ1Hg.