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How to improve the sealing of self-operated regulating valve
Nov 23, 2018

The self-operated pressure regulating valve is divided into three series: self-operating 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 and after the valve. When the pressure point is in front of the valve, the pressure is constant before adjusting the valve; when the pressure point is behind the valve, the pressure is constant after adjusting the valve. . When the valve front and the post-valve pressure are simultaneously introduced into the air chamber of the actuator, the self-operated differential pressure regulating valve can adjust the pressure at both ends of the regulating valve to be constant, and the pressure difference at both ends of the orifice plate installed in the pipe can be introduced into the film. On both sides of the air chamber of the mechanism, a self-operated flow regulating valve is formed, or the flow rate is adjusted by using a self-operated differential pressure regulating valve after the flow is detected. The self-operated pressure regulating valve automatically operates according to the pressure and temperature flowing through the medium in the valve as an energy source, and does not require an external power source and a secondary instrument. Also known as self-operated control valves.
The self-operated pressure regulating valve uses the feedback signal (pressure, differential pressure, temperature) at the output of the valve to transmit the valve to the actuator to drive the valve flap to change the opening of the valve to achieve the purpose of regulating pressure, flow and temperature. The self-regulating valve is a new type of regulating valve. Compared with the manual regulating valve, it has the advantage of being able to adjust automatically; compared to the electric regulating valve, it has the advantage that no external power is required. Application practice proves that in the closed water circulation system (such as hot water heating system, air conditioning chilled water system), the correct use of this valve can easily realize the flow distribution of the system; the dynamic balance of the system can be realized; the system can be greatly simplified Commissioning work; can stabilize the working state of the pump.
The tightness of the self-regulating valve affects the performance of the self-operated regulating valve. Therefore, the sealing performance of the self-operated regulating valve should be continuously improved. The sealing performance of the self-operated regulating valve can be improved by the following five methods:
1. Grinding method: fine grinding, eliminating traces, reducing or eliminating sealing gap, improving the smoothness of sealing surface to improve sealing performance.
2, the use of unbalanced force to increase the sealing ratio pressure method: the sealing force generated by the actuator on the valve core is certain, when the unbalanced force produces an opening tendency to the valve core, the sealing force of the valve core is reduced by two forces, and vice versa, the valve The core produces a pressure-closing tendency, and the sealing force of the valve core is added by the two forces, which greatly increases the sealing specific pressure, and the sealing effect can be increased by 5 to 10 times or more than the former. The general single-sealing valve of dg ≥ 20 is In one case, it is usually a flow-open type. If the sealing effect is not satisfactory, the flow-closing type will be multiplied. In particular, the two-position cut-off regulating valve should generally be used in a flow-closed type.
3. Improve the sealing force method of the actuator: Improve the sealing force of the actuator to the valve core, and it is also a common method to ensure the valve is closed, increase the sealing specific pressure, and improve the sealing performance. Common methods are:
1 moving spring working range;
2 use a small stiffness spring;
3 add accessories, such as with a positioner;
4 increase the pressure of the gas source;
5 Switch to an actuator with greater thrust.
4. Single seal and soft seal method: For the double seal, the control valve can be changed to a single seal, which can generally improve the sealing effect by more than 10 times. If the unbalanced force is large, the corresponding measures should be added. The valve can be changed to a soft seal, which can increase the sealing effect by more than 10 times.
5. Switch to a valve with good sealing performance: In the case of last resort, consider using a valve with better sealing performance. For example, if the ordinary butterfly valve is changed to an elliptical butterfly valve, the cut-off butterfly valve and the eccentric rotary valve can be used instead. , ball valves and shut-off valves specially designed for them.
The installation of the self-operated regulating valve should pay attention to:
1. The pressure point should be taken at the appropriate position of the pressure regulating valve. The pressure regulation before the valve should be greater than 2 times the pipe diameter, and the pressure regulation after the valve should be greater than 6 times the pipe diameter.
2. The self-operated valve can be smaller than the pipe diameter according to the calculation, and the shut-off valve, the cut-off ball valve, the bypass valve and the filter can not be smaller than the pipe diameter.
Self-operated regulating valve installation focus:
1. When the valve is used in gas or low-viscosity liquid medium, usually the ZZY self-operated pressure regulating valve is installed upright on the horizontal pipe, and is flipped or slanted when the position 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. If 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 very clean, the part 3 may not be installed.
5. When the position is not allowed, the bypass valve (manual) can be omitted (we do not recommend it).
6, after the valve group, according to the needs of the user can be equipped with check valves, safety valves and so on.
7. When the valve is used in steam or high viscosity liquid medium, usually the ZZY type self-operated pressure regulating valve is installed on the horizontal pipe in inverted position, and the condenser (steam self-power type) should be higher than the actuator of the pressure regulating valve and lower than The valve is connected before and after. The condenser should be filled with cold water before use and then filled once every 3 months.

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