Application and analysis of valves in engineering design

Application and analysis of valves in engineering design

By analyzing the design conditions and the characteristics of the valve operating principle, static hydraulic balancing valves, self-operated flow control valves, etc. were analyzed. This study from the perspective of reducing the amount of system investment and energy consumption, the need to make the use of two types of valves, and the actual design of the two types of balancing valves debugging and other explanations.

Discussion on the application of static hydraulic balancing valve

Design conditions of hydraulic disorders

An excellent HVAC system can fully ensure that the equipment under full load conditions, all users can obtain the design is the amount of water required, but also to fully ensure the safety and economic efficiency of the system operation, effectively reduce customer complaints about water and water waste and other situations, only such a system can be considered a hydronic balance of the system. If the system does not have these features then it can be called an unbalanced system. In general, if part of the hydraulic system, the user's use of pressure head is greater than the designed pressure head, then the user's actual water flow will exceed the designed flow, which will affect the actual flow of the other loops, we call the hydraulic dislocation in this case for the static hydraulic dislocation, static hydraulic dislocation is usually due to the design of the system or the construction of the reasons, the static hydraulic Disorder is the system itself can not be avoided.

There is also a state in which the actual flow rate of all user terminals in the system is greater than or equal to the value of the system design. In this case, the flow rate can fully satisfy the customer's demand, so this state generally does not cause customer complaints, so this situation will not cause the designer's concern. In general, we use the formula ΔP = SG2 to describe the relationship that exists between the various physical factors of the hydraulic condition in the state of the pipe network of the closed loop (Δp is the differential pressure, S is the pipe network impedance, G is the flow rate).

In the country has not been introduced between the concept of static hydraulic balancing valve, usually the use of globe valves or butterfly valves to control the static hydraulic system. Because these valves have the advantages of simple structure, easy to operate, affordable and so on in the country has been widely used.

Designers should ensure that all temperature-controlled electric valves are fully open under full-load conditions, with the flow rates at the three ends designed to be 33m3/h. However, when the valves are kept 100% open, the actual flow rates at the ends are as follows: End 1 - 39m3/h, End 2 - 35m3/h, End 3 - 31m3/h. This results in a hydraulic imbalance in the system when the pump operates at a head of approximately 19m and a flow rate of about 105m3/h.

The system can be adjusted by adjusting the opening of the first and second section valves. The specific operation is: reduce the differential pressure of the first heating control valve by 40kPa and the second by 20kPa. This ensures that the coil heating control valve resistance at both ends of the three end nodes is maintained at 80kPa. At the same time, it meets the design flow rate of 33m3/h, pump head of 20m, and flow rate of 100m3/h to achieve static balance of the system. Static hydraulic balance of the end branch configuration of the section valve eliminates the need to configure each one individually. Static hydraulic balance valve is not the only solution for this issue.

In the current situation, the vast majority of HVAC hydronic system design is only for the end of the branch for the design of the flow rate of the label, basically will not pay attention to the end of the differential pressure value of the relevant standards and requirements, in the specific operation process, some need to manually complete the balance of the adjustment basically rely on the design, construction, and operation and maintenance personnel to complete the experience of the system belongs to a kind of theoretical support for the system adjustment method. It belongs to a system adjustment method without theoretical support. But from the actual effect, this kind of regulation method without theoretical support does bring some effect for the system of hydraulic disorders.

1.2 Static hydraulic balance valve and hydraulic balance Static液压平衡阀和液压平衡

Static hydraulic balance valve is essentially a multi-functional manual control valve, static balance valve has a single valve multi-functional characteristics, “based on experimental data to be able to characterize, when Δp is a constant state, then the static hydraulic balance valve does not have obvious advantages of regulating, so in the current technological conditions, the use of static hydraulic balance valves directly instead of the traditional hydraulic control valve is not mature enough.

In the current static hydraulic balancing valve market, balancing valve products with flow measurement, valve opening screen, pre-flow, emptying, and other functions are circulating. The use of static hydraulic balancing valves allows for timely flow measurement through a specific instrument and can also act as a switch. Once the balancing valve commissioning is completed, the valve cannot be opened at will due to later maintenance considerations, with the valve body spindle sealing treatment in place. The valve can be adjusted on-site without interrupting the system operation and without compromising the system's overall insulation. However, in terms of cost-effectiveness, the price of static hydraulic balancing valves is not advantageous compared to centrifugal pumps with the same flow rate. Additionally, there are still some issues in the current domestic market regarding static hydraulic balancing valves.

The static hydraulic balancing valve can adjust the flow resistance by controlling its valve opening, which corresponds to a fixed KV value. By measuring the Δp on-site, we can derive the Q value. During engineering commissioning, we use special pressure test holes to measure Δp and determine the corresponding KV value using manufacturer-provided equipment and software. Q is calculated when ΔP = 0.1MPa, considering factors like valve overflow area and roughness accuracy estimation.

Attention needs to be paid to the fact that we use the balance valve to deal with the relevant hydraulic imbalance problem is the need for certain support conditions. Based on the operation mechanism of the static hydraulic balance valve, we can know that the static hydraulic balance valve, but after locking, Δp fluctuations in the value of the water flowing through the valve will cause damage to the constancy of the water, resulting in the calibration of the flow rate value changes.

In the current market, many suppliers of static hydraulic balancing valves have explained that their products have a flow preset function, but in practice, it is difficult to choose a suitable KVS value, because the current market balancing valves do not give a continuous KVS value, and not in accordance with the actual need to give the adjustment value of KVS, therefore, when we set the flow rate according to the KVS value provided by the supplier, there will be a certain deviation, which does not meet the needs of actual regulation. Due to the inability to clarify the field Δp value and the valve opening adjustment caused by the change in the KV value, in the specific process of practice found that if you can not clarify the fouling coefficient of the inner wall of the valve or when the value of its RE does not exceed 3,500, the flow rate of Q value may appear a large deviation in the calculation. Therefore, in the static hydraulic balance judgment, it is necessary to ensure that all the self-operated valves have reached the corresponding design parameter values, to ensure that all the end equipment temperature control valves in the fully open state, and can ensure that its flow rate to meet the design of the required amount.

After completing the installation of the water system, it is necessary to regulate all the valves to ensure that the static water balancing valve flow Q value can reach the design requirements, so as to ensure that the pipe network can be realized in the state of the working conditions of the water balance. At this time, the static water balancing valve is locked on the opening degree, and in the operation process can not be set on the opening degree of the smooth adjustment. At the same time, we should also do a good job of recording the relevant data stored in the system equipment commissioning files, to facilitate the development of future maintenance work.

In addition, due to different equipment suppliers providing computer software with non-uniform KV values, products from different suppliers cannot achieve interoperability in supporting commissioning instrumentation. In static hydraulic balancing valves, all valves are equipped with a cavity behind their hair plugs, which becomes the primary accumulation point for dirt during online operation.

Self-operated flow control valve

2.1 Self-operated flow control valve principle of operation

Self-operated flow control valve is a new type of control valve on the market, self-operated flow control valve compared to the traditional manual flow control valve is superior to its ability to achieve automatic flow adjustment, without the need for external power can be completed. In the actual use of the process found in the closed water circulation system using this self-operated flow control valves can facilitate the realization of the system's flow distribution, dynamic balance, so as to simplify the system commissioning purposes. Based on these advantages, self-operated control valves in the heating and air conditioning project has been favored by many manufacturers. Self-operated flow control valve belongs to a two-valve combination structure, consisting of a manual control valve and automatic balancing valve, they are responsible for setting the flow rate and maintaining a constant flow rate.

In the manual control valve, KVS is the flow coefficient of the manual control valve port, and P2-P3 is the pressure difference coefficient between the two sides of the manual control valve port. The size of the KVS is closely related to the degree of openness. If the openness is unchanged and the P2-P3 is unchanged, the C does not change. The P2-P3 is kept unchanged mainly depends on the balancing valve. For example, when the import and export pressure difference Pl-P3 becomes larger, the use of dynamic pressure film and spring force prompts the balance switch to automatically adjust the small, P1-P2 will become larger to maintain P2-P3 unchanged. Conversely, when P1-P3 becomes smaller, the balance switch automatically adjusts the large, P1-P2 will become smaller to maintain P2-P3 unchanged. The size of each valve of the manual switch regulator group has a corresponding flow rate, and the relationship between the angle of each valve open and the flow rate is determined by the test bench experiment standard.

2.2 Self-operated flow control valve in the water mixing system applications

Self-operated flow control valves do not need to rely on external power but rely on their own media pressure difference to achieve control, self-operated flow control valves are equipped with automatic flow control components, the components can realize the flow equilibrium, through this function from the fundamental solution to the problem of hydraulic imbalance. Self-operated flow control valves are very simple to install and easy to adjust, the use of the process of consuming less energy, which increases the heating area can reach between 25% -30%, greatly improving the stability of its operation, to ensure the quality of heating. When we carry out the transformation of the water mixing system, first of all, the hydraulic calculation, the heating area, the ring flow to and the corresponding heating pipe diameter and other factors to analyze, according to these data information to select the appropriate flow control valve, according to the temperature to regulate the size of the flow, and then with the help of self-operated flow control valves with a unique function to achieve stability of the mixing of the water pressure, flow, and temperature, which fully ensures that the water mixing station This can fully ensure that the mixing station can obtain a relatively stable flow between the system to ensure the balance of the operation.