The self-operated pressure regulating valve is divided into three series: self-operated pressure, differential pressure and flow regulating valve. The self-operated pressure regulating valve is divided into two types according to the position of the pressure taking point: before the valve and when the pressure taking point is in front of the valve, it is used to adjust the constant pressure before the valve; when the pressure taking point is behind the valve, it is used to adjust the pressure after the valve is constant. . When the pressure before and after the valve is introduced to both sides of the air chamber of the actuator at the same time, the self-operated pressure difference regulating valve can adjust the pressure at both ends of the regulating valve to be constant, and the pressure difference between the two ends of the orifice plate installed on the pipeline can be introduced into the film for execution. On both sides of the air chamber of the mechanism, a self-operating flow regulating valve is formed, or the flow is adjusted by using a self-operating pressure difference regulating valve after detecting the flow in other ways. The self-operated pressure regulating valve relies on the pressure and temperature of the medium flowing through the valve to drive the valve to work automatically as an energy source, without the need for an external power supply and secondary instruments. Also known as self-operated control valve.
Self-operated pressure regulating valves use the feedback signals (pressure, pressure difference, temperature) at the output end of the valve to pass through the signal tube to the actuator to drive the valve flap to change the opening degree of the valve to achieve the purpose of adjusting pressure, flow and temperature. Self-acting control valve is a new type of control valve. Compared to a manual regulating valve, it has the advantage of being able to adjust automatically; compared to an electric regulating valve, it has the advantage of not requiring external power. Application practice proves that in closed water circulation systems (such as hot water heating systems, air-conditioning chilled water systems), the correct use of this valve can easily achieve the system's flow distribution; can achieve the system's dynamic balance; can greatly simplify the system Commissioning work; can stabilize the working state of the pump.
The sealing performance of the self-operated control valve affects the performance of the self-operated control valve. Therefore, the sealing performance of the self-operated control valve must be continuously improved during use. The sealing performance of the self-operated control valve can be improved in the following five ways:
1. Grinding method: Fine grinding to eliminate traces, reduce or eliminate sealing gaps, improve the smoothness of the sealing surface, and improve sealing performance.
2. Use the unbalanced force to increase the sealing specific pressure method: The sealing pressure generated by the actuator on the valve core is constant. When the unbalanced force has a tendency to open the valve core, the sealing force of the valve core is subtracted from the two forces. The core has a pressure-closing tendency, and the sealing force of the valve core is the sum of the two forces, which greatly increases the specific pressure of the seal, and the sealing effect can be increased by 5 to 10 times more than the former. Generally, single-seal valves with dg≥20 are the front In one case, it is usually a flow-open type. If the sealing effect is not satisfactory, the flow-closed type will be used, and the sealing performance will be doubled. Especially the two-position cut-off control valve should generally be used as a flow-closed type.
3. Improving the sealing force of the actuator: Improving the sealing force of the valve core of the actuator is also a common method to ensure that the valve is closed, increase the specific pressure of the seal, and improve the sealing performance. Common methods are:
① Mobile spring working range;
② Use a small stiffness spring;
③ Add accessories, such as with positioner;
④Increase the gas source pressure;
⑤ Switch to an actuator with greater thrust.
4.Single-seal and soft-seal method: Regarding the double-seal control valve, single-seal can be used, which can usually improve the sealing effect by more than 10 times. If the imbalance force is large, corresponding measures should be added. The valve can be replaced with a soft seal, which can improve the sealing effect by more than 10 times.
5. Switch to a valve with good sealing performance: In the case of last resort, you can consider switching to a valve with better sealing performance. For example, if you change an ordinary butterfly valve to an oval butterfly valve, you can also use a cut-off butterfly valve and an eccentric rotary valve. , Ball valves and specially designed shut-off valves.
Attention to the installation of self-regulating valve:
1. The pressure taking point should be taken at an appropriate position of the pressure regulating valve. The pressure regulating before the valve should be greater than 2 times the diameter of the pipeline, and the pressure regulating after the valve should be greater than 6 times the diameter of the pipeline.
2. The self-operated valve can be smaller than the diameter of the pipeline according to the calculated diameter, while the stop valve, shut-off ball valve, bypass valve, and filter cannot be smaller than the diameter of the pipeline.
Key points of self-regulating valve installation:
1. When the valve is used in gas or low-viscosity liquid medium, usually the ZZY self-operated pressure regulating valve is installed on the horizontal pipe upright, and it is installed upside down or obliquely when the space is not allowed.
2. In order to facilitate on-site maintenance and operation, appropriate space should be left around the pressure regulating valve.
3. When the medium is clean gas or liquid, the pre-valve filter may not be installed.
4. The diameter of the pressure regulating valve is too large (when DN≥100), there should be a fixed bracket. When it is confirmed that the medium is clean, piece 3 may not be installed.
5. When the position is really not allowed, the bypass valve (manual) can be omitted (we don't recommend it).
6. After the valve group, the user can choose check valve, safety valve, etc. as required.
7. When the valve is used in steam or high viscosity liquid medium, usually the ZZY self-operated pressure regulating valve is installed on the horizontal pipe upside down. The condenser (self-operated for steam) should be higher than the actuator of the pressure regulating valve and lower than The valve takes over before and after. The condenser should be filled with cold water before use, and once every 3 months.