What Is a Balancing Valve?

The balance valve is a special function valve. There is nothing special about the valve itself, only the difference between the function and the field. In some industries, due to the large pressure difference or flow difference of the medium (all kinds of flowable substances) in each part of the pipeline or container, in order to reduce or balance the difference, between the corresponding pipelines or containers A valve is installed to adjust the relative balance of pressure on both sides, or to achieve the balance of flow through the method of flow division. This valve is called a balance valve.

The balance valve is a valve that performs dynamic and static balance adjustment under hydraulic conditions. There are three types of balancing valves: static balancing valves, dynamic balancing valves and differential pressure independent balancing valves. Static balancing valve is also called balancing valve, manual balancing valve,

The balancing valve is a regulating valve with a special function of digital lock.

When the operation of the system is adjusted by a centralized quantity (such as the speed adjustment of a water pump, etc.), a balancing valve and a self-operating differential pressure balancing valve cannot be used. Because this adjustment is achieved by changing the water volume, the hydraulic conditions of the system are changed during the adjustment. Therefore, if a balancing valve is used, some valves will work normally, but the system flow is too large (exceeding the thermal load Corresponding flow), some valves still fail to meet the flow requirements when fully opened, and some valves cannot work normally because the pressure difference between the two ends cannot reach the starting pressure difference, that is, the confusion of flow distribution occurs. Obviously, centralized adjustment of the system cannot be achieved due to the presence of the balancing valve. At this time, if a manual regulating valve is used, when the total flow of the system is increased or decreased, the flow of each branch and each user can be increased or decreased in the same proportion, that is, the centralized adjustment of the system can be transmitted to each end device. When the operation of the system is qualitatively adjusted, a balance valve and a self-operating differential pressure balance valve can be used, because this adjustment method only changes the water supply temperature, and has nothing to do with the hydraulic conditions of the system, that is, the hydraulic conditions of the system are not changed Case, communicate the adjustments to each user and device. The balance valve can be used to absorb the pressure fluctuations of the network and keep the flow of the controlled load constant. The use of a balancing valve can absorb pressure fluctuations in the network and overcome internal disturbances (changes in resistance inside the controlled loop) to maintain a constant pressure differential across the controlled loop. When the system adopts the qualitative regulation of changing the flow rate in stages, although the flow rate does not change in each stage. However, if a balancing valve is used, the control flow or pressure difference must be set at each flow stage, which brings great inconvenience to operation management, so it should not be used. ^[1]

1. Ideal adjustment performance; 2. Excellent cut-off function;

3. Open status display accurate to 1/10 laps;

4. The theoretical flow characteristic curve is an equal percentage characteristic curve;

5. National patented opening and closing locking device;

6. Corresponding to each full lap

(1) Linear flow characteristics, that is, when the pressure difference between the front and back of the valve is unchanged, the flow rate and the opening degree are generally linear; (2) There is an accurate opening degree indication; (3) There is an opening degree locking device, and non-managers cannot casually Change the opening degree; the meter connection can conveniently display the pressure difference before and after the valve and the flow through the valve. Although the balance valve has many advantages, there are still many problems in its application in air conditioning water systems. If these problems are not solved well, the characteristics of the balancing valve will not be fully revealed. The function of the balancing valve is to regulate the predetermined flow of each distribution point (such as each building) in the system. Equipped with a balancing valve at the entrance of each building,

The principle of the balancing valve is the reverse regulation in the valve body. When the pressure at the inlet increases, the diameter is automatically reduced to reduce the change in flow, and vice versa. If reversed, this set

Kv is the valve coefficient of the balance valve. Its definition is: when the differential pressure before and after the balance valve is 1 bar (about 1kgf / cm2), the flow value ( m / h) flowing through the balance valve. When the balance valve is fully open, the valve coefficient is equivalent to the flow capacity of an ordinary valve. If the opening degree of the balancing valve does not change, the valve coefficient Kv does not change, that is, the valve coefficient Kv is determined by the opening degree. Through the actual measurement to obtain the valve coefficient under different opening degrees, the balance valve can be used as a quantitative

The balance valve is equivalent to a throttling element whose local resistance can be changed. For incompressible fluid, it can be obtained from the flow equation: where: Q-the flow through the balance valve -the resistance coefficient of the balance valve P1-the front of the valve Pressure P2-pressure behind the valve F-cross-sectional area of the balance valve take-over area -the density of the fluid can be seen from the above formula, when F is constant (that is, for a certain type of balance valve), the pressure drop P1-P2 before and after the valve does not As time changes, the flow rate Q is only affected by the resistance of the balancing valve. When increases (the valve is closed), Q decreases; otherwise, decreases (the valve opens) and Q increases. The balancing valve is to change the resistance coefficient by changing the opening degree of the valve core to achieve the purpose of adjusting the flow rate. The use of static balance valve static

1. Dynamic balancing valve (principle is to prevent the end flow from being affected by the pressure fluctuation of the pipe network, and is suitable for off-line pipelines and variable flow water systems) (1)

The balance valve is a special function valve with a quantitative measurement function and an adjustment function. When the system is commissioned, the commissioning personnel adjusts the balance valve through a dialogue with a dedicated intelligent instrument to achieve the hydraulic balance of the system. It has good flow regulation characteristics, and the relative flow has a linear relationship with the relative opening. There is an accurate valve opening indication, and the minimum reading is 1% of the full valve opening. Reliable opening degree lock memory device, the valve opening degree can be restored to the original

Easy to use: The construction of the project is more flexible, and the installation of the project or the use of equipment in stages will not affect the water system balance; easy to change: when the water system in some areas needs to be redesigned, it will not affect the water system design and balance in other areas ; Reduce power consumption: As the entire water system is balanced, the refrigeration unit (boiler, heat exchanger) and water pump can be guaranteed to operate in the best working condition, which has obvious energy-saving effects; reduce wear and reduce waste: because the water flow is not guaranteed It will exceed the original design, guarantee the durability of all equipment, avoid copper pipe loss caused by excessive flow; improve safety: because the flow balance of the water system is performed automatically, the possibility of artificial destructive adjustment is eliminated. For designers: reduced workload, more flexible and lightened workload: no need to perform tedious resistance calculations for the entire pipeline, speeding up

Installation of counterbalance valve

1) Remove the protective caps on both sides of the flange end, and rinse the valve with the valve fully open.

2) Before the installation of the balancing valve with the actuator, the whole machine should be tested according to the specified signal (electricity or gas) (to prevent the use of vibration due to transportation from affecting the performance), and it can be installed on the line after it is qualified (the wiring is according to the electric actuator circuit diagram).

3) Before preparing to connect to the pipeline, flush and remove the impurities remaining in the pipeline (these materials may damage the valve seat and the ball core).

4) During the installation, please do not use the actuator part of the valve as a lifting point to avoid damage to the actuator and accessories.

5) This category

First, the balance valve

The balancing valve is correctly understood as a valve for balancing hydraulic conditions. From this concept, all valves used for hydraulic working condition balancing, such as regulating valves, pressure reducing valves, self-operating flow control valves, and self-operating differential pressure control valves, should be regarded as hydraulic working condition balancing valves-balancing valves. The product called balancing valve on the market is only a manual regulating valve with a flow test function. Static balancing valve refers to a manual regulating valve or a manual balancing valve. Dynamic balancing valve refers to self-operated flow control valve and self-operated pressure difference control valve. Self-operated flow control valve was also called self-operated flow controller and self-operated balance valve. Self-operated differential pressure control valve is also called Automotic Balamce Valve in Northern Europe. ^[1]

Second, hydraulic conditions and hydraulic conditions balance

Generally speaking, the heating and air-conditioning pipe networks are closed-loop pipe networks. The hydraulic conditions refer to the pressure at each point of the system, and the flow rate and pressure difference of each pipe section. From the formula P = SG2 Ppressure difference or resistance loss Sresistance coefficient of pipe section or system Gflow rate of pipe section or system, flow and pressure are related parameters, and the regulation of flow and pressure are mutual means And purpose. The decompression method is to reduce the flow of the upstream pipeline; reducing the flow must also reduce the pressure at the front of the pipeline or increase the pressure at the rear of the pipeline. The change of flow rate will inevitably lead to the change of pressure; for the system with constant S value, the change of pressure difference must be caused by the change of flow rate. Therefore, it is said that there is no pressure control valve that does not affect the pressure, and there is no pressure control valve that does not affect the flow. Hydraulic condition balance refers to the rational distribution of fluids. In the heating and air-conditioning pipe network, water is the heat carrier medium, and the reasonable distribution of water flow is the basis of thermal condition balance. Taking the heating system as an example, the designer carried out under the imaginary situation that each branch flow rate is the design value when performing the hydraulic working condition calculation. Due to the limitation of the pipe and the maximum flow rate, it is almost impossible to achieve hydraulic balance in the design. This will inevitably cause the near-end resistance coefficient to fail to reach the design ideal state, resulting in an imbalance in which the near-end flow is too large and the far-end flow is insufficient. Because the hydraulic working condition is designed as a design hydraulic pressure chart, this hydraulic pressure chart must be formed by the valve balance adjustment in actual operation. The process of adjusting hydraulic conditions with a valve is a process of establishing a reasonable hydraulic pressure map. Under a reasonable design, the two hydraulic pressure maps will combine well. Because the operating hydraulic condition is formed by the intersection of the pump's working curve and the external network characteristic curve. For the external network characteristic curve P = SG2, because the S value of the parallel near-end branch will be smaller than the design value, the total S value will be much smaller than the design value. Power, low efficiency point operation. In severe cases, it may occur that the shaft power is greater than the motor nameplate power, and the motor exceeds the rated current until the motor burning accident occurs. The process of adjusting the net is to increase the proximal resistance with a balancing valve, so that the S value of the proximal branch is increased to the design value, and the total S value is increased to the design value. Make the far and near flow distribution even and reasonable, and the circulating water pump runs under the design conditions to achieve the purpose of saving heat, electricity and improving the quality of heating. Operators often misunderstand some of the unbalanced hydraulic conditions: (1) the pump output is insufficient, and the actual head of the pump is less than the nameplate head, resulting in the end of the water. In fact, due to the small resistance of the proximal branch line and the large flow, the remote flow is small. (2) The resistance of the boiler or heat exchanger is large, and all boilers or heat exchanger manufacturers have stated that the resistance is far less than the actual resistance. In fact, the increase of the total circulating water volume will inevitably lead to an increase in the resistance of the boiler heat exchanger. Water flow increased by 40% and resistance increased by 100%. (3) The boiler output is insufficient, in fact, the temperature difference between the supply and return water cannot be greater after the flow increases. Of course, the abnormal coal quality and wind system may also cause boiler output problems. ^[1]

Third, the water pressure map analysis of the adjusting network and the installation position of the balance valve

The process of adjusting the net is a process in which each branch reaches a reasonable flow using a balancing valve. The proximal end pressure head is greater than that required by the user, which will inevitably lead to excessive flow. The rich head must be consumed by the valve. . If the user's return pipe is equipped with a balancing valve to adjust the screen, P2 is approximately equal to P1, and the pressure line of P3 is almost parallel to P1. The indoor water supply pressure is P2 and the return water pressure is P3. If the pressure is too low, the operation will be emptied. If the pressure is too high, the pressure breakdown of components with a lower pressure rating (such as a radiator) will occur. Therefore, for the pipe network with large terrain height difference, the installation position of the balance valve should be considered according to the above factors. That is to say, in the low-lying terrain of the building group, the balance valve should be installed in the water supply to ensure that there is no pressure indoors; in the higher terrain position, the balance valve should be installed in the backwater to ensure that the user does not empty. For large-scale direct-connected pipe networks, such as the condensing steam heating pipe network of a power plant, the heating radius is large, and the pressure difference between the water supply and the return water of the external network is very large. Therefore, special consideration should be given to the installation position of the balancing valve. The pressure difference between the backwater supply pressure of the external network of the condensing steam supply pipe network of a power plant in Yantai is 52m water column. Considering the pressure resistance of the radiator, the backwater pressure at the end is set to 0.35MPa (35m water column), and the backwater pressure at the front end is only 0.1MPa ( 10 meters of water column), and the front-end water supply pressure is up to 0.62MPa (62 meters of water column). If the balance valve is installed on the return pipe, the return water pressure P3 of the accused user may be close to 0.6MPa, which will certainly cause the pressure of the radiator to be destroyed; The balance valve is installed on the water supply pipe, and the water pressure P2 of the near-end user is only a dozen meters of water column, which will inevitably lead to empty operation. Therefore, from the design, a solution of installing a balance valve for both the return and return water should be adopted to form the hydraulic pressure diagram of Figure 4. The specific method is to install a self-operated flow control valve on the water supply pipe at the entrance, and install a manual balance valve on the branch return pipe of the building group with a terrain height difference of not more than 10 meters. Here the self-operated flow control valve is responsible for controlling the distribution flow; the manual balance valve adjusts the pressure so that the pressure in front of the valve reaches the full water operating condition of 0.25 MPa. The self-operated flow control valve only controls the pressure according to the flow rate. If it is installed on the return pipe, it is not necessary to manually adjust the pressure, and a pressure damage accident has occurred. When the self-operated valve is installed when the water supply is not manually adjusted for pressure, it may run out and affect the heating effect, and an accident may not occur. ^[1]

Fourth, the concept of user active variable flow and heat source active variable flow

For the heating system under the traditional heating system, it is an evenly distributed heating mode. This heating mode generally adopts a constant-flow quality-regulated heating method. There are also a few large-scale pipe networks that adopt quality and adjustment methods for the purpose of saving operating power. However, under the premise of average heat generation, the change of fluid flow is only determined by the change of outdoor air temperature. Therefore, the control method only considers the single parameter of outdoor temperature to control the speed of the heat source circulation pump to achieve variable flow operation. This variable flow operation can be defined as the active source variable flow method. Under the operation mode of heat metering charge, the change of heating load and circulating water flow depends on the user's needs, and the change of the total circulating flow of the system depends on the user's change. This variable flow mechanism can be defined as the user's active variable flow mode. Some people in the industry have proposed that the metering and charging indoor system adopts a horizontal span pipe system in an attempt to continue to operate at a constant flow rate. It is estimated that regardless of whether the horizontal span can achieve flow operation, the item of constant flow operation mode wastes operating power. Abolished. This metering and charging flow control scheme is based on the following scheme as the best feasible solution: take 3 to 5 terminal supply and return water pressure difference signals as the control signals of the thermal cycle flow, and the circulating water pump when all the pressure difference signals are greater than the set value Reduce the speed. When any pressure difference is less than the set value, the circulating water pump increases the speed. ^[1]