First, the balance valve Balance valve correctly understood should be balanced hydraulic conditions valve. From this concept all the valves used for the balance of hydraulic conditions, such as regulating valves, pressure reducing valves, self-operated flow control valves, self-operated pressure differential control valves should be regarded as hydraulic balance valve - balance valve. The products on the market called counterbalance valves are just a kind of manual control valve with the function of flow test. Static balance valve refers to manual control valve or manual balancing valve. Dynamic balance valve is self-flow control valve and self-pressure control valve. Self-acting flow control valve has also been called self-flow controller, self-balancing valve. Self-operated differential pressure control valve is also called Automotic Balamce Valve in Northern Europe. Second, the hydraulic conditions and the balance of hydraulic conditions Generally speaking, heating, air conditioning pipe network are closed-loop pipe network, the hydraulic conditions refers to the system pressure at all points, the various sections of the flow, pressure. From the formula △ P = SG2 △ P - pressure drop or loss of resistance S - pipe or system resistance coefficient G - pipe or system flow shows, flow and pressure are related parameters, flow and pressure control each other means And purpose. Decompression means is to reduce the flow of the upstream pipe; reduce the flow will inevitably reduce the pressure on the point before the pipeline or increase the pressure at the point after the pipeline. Flow changes will inevitably lead to pressure changes; S value unchanged system, pressure changes must be due to changes in flow. So there is not a flow control valve that does not affect pressure, nor a pressure control valve that does not affect flow. Hydraulic conditions balance refers to the rational distribution of the flow. In heating and air conditioning pipe network, water is a heat carrier medium, the rational distribution of water flow is the basis for the balance of thermal conditions. Taking the heating system as an example, the designer carries out the hypothetical situation when the branch flow is the design value during the calculation of hydraulic conditions. Due to the limitation of tubing and maximum flow rate, it is almost impossible to achieve hydraulic balance in design. This will inevitably cause the proximal resistance coefficient can not reach the ideal state of the design, the formation of the proximal flow is too large, the lack of remote flow disorders. Because of hydraulic design into a design hydraulic map, and the actual operation of the hydraulic map must be balanced by the valve to form. The process of regulating the hydraulic conditions with a valve is a process of establishing a reasonable hydraulic pressure chart. The two hydraulic pressure plans will work well when the design is reasonable. Due to the operation of hydraulic conditions is the working curve of the pump and the characteristics of the formation of the outer network formed. For the external network characteristic curve △ P = SG2, the S value of the near-end branch in parallel will be less than the designed value, resulting in the total S value far less than the designed value. The circulating pump operates under the condition of small lift and large flow, Power, low efficiency point of operation. Serious shaft power may appear greater than the motor nameplate power, the motor over-rated current, until the burning motor accident. Network transfer process is to increase the proximal balance valve resistance, so that the value of the proximal branch S increased to the design value, the total S value increased to the design value. So that far and near the flow distribution is reasonable and reasonable, circulating pump running in the design conditions, to heat, power saving, improve the quality of heating purposes. Workers often have some misunderstanding of some imbalances in hydraulic conditions: (1) the pump output is insufficient, the actual pump head is less than the nameplate lift, leading to the end of the speech too much water. In fact, the resistance of the near-end feeder is small and the flow rate is large, resulting in a small flow at the far end. The working point of the pump is shifted to a large flow rate, a small lift and an inefficient operating point. (2) Boiler or heat exchanger resistance, all boiler or heat exchanger manufacturers are far less than the nominal resistance of the resistance. In fact, the increase of the total circulating water will inevitably lead to speech boiler heat exchanger and other resistance increases. Water flow increased by 40%, resistance increased by 100%. (3) Inadequate boiler output In fact, the flow rate increases after the supply and return water temperature difference can not be greater. Of course, abnormal coal quality and wind system may also contribute to the issue of boiler output. Third, the transfer network water pressure analysis and balance valve installation location Network transfer process is to use the balance valve to make each branch to achieve a reasonable flow of the process. Proximal head pressure than the user needs to use head pressure will lead to excessive traffic. Must use the valve to consume the rich indenter Wealthy indenter = capital pressure head - need to use pressure head) Figure 2 shows the user valve and the pressure point, if the user supply pipe installation balance valve network, then P3 is approximately equal to P4, P2 pressure line As shown in Figure 3, almost parallel P4. If user return pipe installs balance valve, P2 is approximately equal to P1, P3 pressure line is almost parallel to P1. Indoor actual water pressure is P2, return pressure is P3. If the pressure is too low will cause the operation of emptying, the pressure is too high lead to lower pressure level of the components (such as radiators) pressure damage. Therefore, the height of the terrain elevation pipe network should be considered the above factors balance valve installation location. In the low-lying terrain at the group balance valve should be installed in the water supply to ensure that the family can not afford to pressure; in the higher position of the balance valve should be installed in the backwater to ensure that users do not emptied. For large-scale direct-coupled pipe network, such as power plant condensate heating pipe network, a large heating radius, external network for a large pressure drop, so the installation of counterbalance valve should be given special consideration. Yantai, a power plant condensate supply pipe network outside the network pressure 52 meters of water supply and drainage pressure, considering the radiator pressure capacity, the end of the backwater pressure is set to 0.35MPa (35 meters of water), the front return water pressure of only 0.1MPa 10 meters water column), while the front-end water supply pressure is as high as 0.62MPa (62 meters water column). If the balance valve is installed on the return pipe, the back pressure P3 of the charged user may be close to 0.6MPa, Balance valve installed in the water supply pipe, the user's water pressure P2 near the end of only a dozen meters of water will inevitably lead to operational emptying. Therefore, from the design should be taken for the return valve are installed balance valve scheme to form the hydraulic diagram of Figure IV. The specific approach is to enter the water supply pipe to install self-flow control valve, in the terrain elevation does not exceed 10 meters of the branch back to install a manual balance valve. Here self-flow control valve is responsible for controlling the distribution of flow; manual balancing valve to adjust the pressure so that the valve pressure reaches 0.25MPa full water operating conditions. Self-operated flow control valve based only on the size of the flow "肓 目" control the pressure, if installed on the return pipe, not to be manually adjusted pressure, pressure failure has occurred. Self-power valve installed in the water supply is not manually adjust the pressure, may run empty and affect the heating effect, impossible accident. Fourth, the user active variable flow and the concept of active variable flow heat For the heating system in the traditional heating system is an evenly distributed heating mode, this heating mode generally take a constant flow qualitative adjustment heating mode. There are also a few large-scale pipe network for the purpose of saving electricity to run, take the quality and tune the way. However, under the premise of average heat generation, the change of flow depends only on the change of outdoor temperature. Therefore, the control method only considers the single parameter of outdoor temperature to control the rotation speed of heat source circulating pump to realize variable flow operation. This variable flow can be defined as the heat source active variable flow way. Under the operation mode of heat metering and charging, the change of heating load and circulating water flow depends on the user's needs. The change of the total circulating flow of the system depends on the change of the user. This variable flow mechanism can be defined as the user's initiative to change the flow mode. There are some people in the industry proposed charging system of indoor systems across the horizontal pipe system, in an attempt to follow the constant flow mode operation, regardless of whether the level of cross-over whether the flow can be achieved, the only way to run on a constant flow of running power should be Be abolished. This metering and charging flow control scheme, the following programs for the best possible solution: Take 3-5 end of the return water pressure difference signal for the thermal cycle flow control signal, when all the differential pressure signals are greater than the set value of circulating water pump Reduce speed, when any one pressure drop is less than the set value, the circulating pump to increase speed. Fifth, the performance and use of balance valve 1, manual balance valve Manual balance valve with low cost, long life and other components to use the advantages of small branch pipe network can also facilitate the balance of the hydraulic conditions. Only manual balance valve can be used for heat source variable pipe network, because only the manual balance valve can ensure the consistent change of the flow, and all self-balancing valves can not guarantee the active heat flow of the heat source. Such as the aforementioned large straight pipe network manual balancing valve can be used to adjust the pressure conditions. 1.1 Manual balance valve characteristic curve 1) Cut-off valve characteristic curve 2) Linear characteristic valve Actual working curve (Valve weight 0.2) 3) Linear characteristic 4) Equal percentage characteristic curve The characteristic curve of the valve determines the regulating performance of the valve, Of the flow curve, if 95% -100% of the traffic flow is considered meaningless, then the opening from 0-5% of the flow to achieve the full change, such a valve can not be used as a balance adjustment of hydraulic conditions . Since the theoretical characteristic curve of the valve is tested under a constant pressure difference, the actual working condition is that the valve has a large pressure difference before and after the valve is opened at a small opening degree, and the pressure difference before and after the large opening degree is small, leading to the valve dG / dC value in a small opening becomes larger, smaller opening in the large opening, so that the actual work of the valve to open the direction of the deviation, the smaller the valve the greater the deflection, the linear characteristics of the valve due to the actual performance Offset will lead to the effective adjustment of the valve opening space becomes smaller, so the theoretical curve of the valve string below the arc as a percentage of the characteristics as well. Equal percentage (logarithmic) characteristic curve valve, the valve operating at 0.3-0.5 actual working curve may be close to the linear characteristics. 1.2 Cavitation Vibration Valve Usually valve in the case of small opening valve port flow rate is too high, the valve will form a strong turbulent spiral area, the spiral core pressure is very low, where the pressure is lower than the corresponding water temperature The flash of water vapor at saturation pressure can lead to the phenomenon of gas-water hammer: severe noise, vibration of valves and pipes, damage of valves, pipes and pipe supports. To prevent the occurrence of such accidents should first consider the design of the valve spool valve seat and valve seat in the small opening to form a narrow throttle flow, constrained the formation of turbulence swirl; followed by the valve when you try to increase the valve To prevent the valve from operating at a small opening. In addition, try not to pressure conditions involved in the balance valve installed in the lower water temperature on the backwater. 2, self-flow control valve 2.1 self-operated control valve works (1) orifice flow meter - pilot valve - the principle of the main valve. The main valve in front of a flow orifice plate, pilot sensing, comparison before and after the orifice pressure difference, such as the pressure difference greater than the set pressure, means that the flow exceeds the set flow, the pilot valve to control the main valve to close the valve action. If the sensing pressure difference is less than the set pressure difference, it means that the flow rate is less than the set flow rate, and the pilot valve controls the main valve to open the valve. Pilot valve set the pressure difference adjustable, adjust the small set small pressure difference, you can adjust the small adjustable small flow. As the orifice flowmeter flow pressure corresponding to the relationship between the former flow influence is extremely heavy, if the required flow rate accuracy of 10%, you must have 10d before the valve above the straight pipe, and this project is very difficult to protect in practice. In addition this valve factory flow adjustable range is very small, to maintain the accuracy of flow under the premise of the flow ratio can not exceed 2: 1 adjustable. (2) "Kv · = constant" principle, the free spring and the pressure sensitive membrane form the valve switch power system △ P / S = εL S-sense membrane working area, ε-spring Hook coefficient, L- valve stroke It can be seen Each stroke position of the valve determines the value of ΔP. If Kv of the valve position is inversely proportional to, then K = Kv · is a constant value. The principle of the valve initially made flow rate can not be adjusted flow limiter, adjustable flow in recent years, the production is made of a multi-tube channel, set the flow through the plugging adjustment; the other is to use a manual valve to change self-valve Kv and the relationship between the trip, but this method is difficult to guarantee Kv and the inverse relationship between the position of each adjustment, resulting in adjustment bit flow control accuracy is not high. In addition, some products use corrugated pipe to make pressure sensitive film and free spring integrated products. Because stainless steel corrugated pipe is in flowing dead zone, when chloride ion content in water is high, it is easy to produce corrosion. (3) Self-operated differential pressure control valve and manual control valve principle. This principle is now the most widely used flow control valve made. Manual control valve position of each opening corresponds to a Kv value by the self-operated pressure control valve to control the pressure difference before the manual control valve unchanged, then G = Kv · unchanged, only need to adjust the flow control valve manual adjustment Kv value. Flow control accuracy of this valve depends on the accuracy of the differential pressure control valve, the pressure difference △ P = N / SN - spring force S - pressure sensitive diaphragm working area spring force in the valve stroke will vary, but the H / △ L = 1/10 H-- maximum self-displacement valve displacement △ L - spring pre-compression △ P changes only ± 5%, flow accuracy of up to 3%. This self-flow control valve has the drawback of the valve has the minimum working pressure requirements, the general requirements of the product minimum working pressure 20KPa, if installed in the most adverse circuit, will inevitably require circulation pump to increase the working lift of 2 m water column, so Near-end installation should be taken, distal uneasy approach. Users from the heat source is greater than the heating radius of 80% should not install this self-flow control valve. (4) With the self-operated pressure control valve directly control the indoor flow resistance coefficient S, the average heating in the premise of the same value, indoor design flow G, △ P = SG2, by controlling indoor supply and return pressure Poor, the same can control the circulation flow, adjust the control pressure can adjust the circulation flow. Use this approach to regulate traffic, but must rely on portable flow test equipment such as ultrasonic flowmeter. This way for the remote user, the valve does not increase the pressure head. 2.2 Self-acting flow control valve applicability Self-flow control valve in large-scale pipe network applications can make the flow distribution work easier and more convenient. In particular, multi-heat pipe network, heat switch operation will not affect the user traffic. But for the variable flow pipe network can not be used self-flow control valve. In the case of an active variable flow of the heat source, the near-end circuit maintains the same flow but the flow of the far-end circuit will be severely under-flowed. In the case of hot users active variable flow, the user initiative to tune the smaller flow, self-flow control valve will open a large valve, try to maintain the original flow, until the full failure. When the user initiatively adjusts the flow, the self-operated flow control valve will close the small valve until it is fully closed. That is only self-flow control valve failure, the user's initiative to meet the traffic requirements. 3, self-operated pressure control valve 3.1 self-operated pressure differential control valve of significance (1) self-operated pressure control valve consumption system of the rich pressure head. (2) Self-operated differential pressure control valve play a role in isolating the user flow changes interfere with each other. Some people in the two functions think that the thermostatic valve on the radiator can work, in fact, if the temperature control valve to produce such a role will inevitably lead to the temperature control valve in a small opening, even under vibration conditions jobs. This is very unfavorable to the thermostatic valve, the initial hope of the thermostatic valve is limited to the use of free heat, and many of our industry's hopes of placing it too large. (3) Self-operated differential pressure control valve to isolate the user traffic changes interfere with each other. 1, the original work point 2, the user automatically adjust the flow of the formation of the work point 3, the circulating pump speed - the formation of operating pressure differential valve 4, the circulating pump speed differential pressure valve operating point (4) for the electric control Automatic control system, isolated from the regulation of the parallel branch interference, to avoid unnecessary movement of the automatic control system to improve the stability and reliability of the control system. (5) play a special operating conditions of the current limit. In start-up and special cold conditions, the heat demand of the user will exceed the heating capacity of the heat source. The self-operated differential pressure control valve will effectively limit the near-end flow so that the remote user can achieve the predetermined heating effect. 3.2 Self-pressure control valve selection parameters. (1) adjustable pressure difference Under normal circumstances, the design is difficult to accurately calculate the indoor resistance, and indoor resistance (at the design flow) may vary between 0.01-0.03MPa, so the adjustable self-pressure than the minimum should be 1: 3 above. (2) The maximum and minimum flow coefficient Kv The maximum flow coefficient is the valve full open flow coefficient; the minimum flow coefficient is the valve full close bit leakage factor. These two valve parameters of the valve application selection is crucial, the valve supplier must be measured and disclosed these two parameters. The maximum flow coefficient should be able to ensure that the design flow under the minimum pressure head; minimum flow coefficient should be able to ensure that the maximum maximum flow under the pressure head to adjust the conditions may be the minimum flow value. (3) Differential pressure control accuracy should reach 10% to ensure flow accuracy of 5%. 3.3 In the household control is not installed heat meter cases, self-pressure control valve will also play a role in the allocation of constant flow. The adjustment method only needs to adjust and control the differential pressure flow to reach the designed flow rate. And self-flow control valve the same branch flow adjustment do not interfere with each other to adjust the flow can be completed once. Therefore, in most of the projects that implement household-controlled metering and charging, self-operated differential pressure control valves should also be adopted. In the unmetered charges before the differential valve can also balance the distribution of flow, to avoid the installation of gauges, to replace the valve.