1 self-operated pressure control valve classification and working principle
Classification of 1.1 Self-pressure regulating valve
1) according to the valve, valve control is divided into two categories: self-operated valve (valve) control valve; self-operated valve (pressure) control valve.
2) according to whether the device with a command is divided into two categories: direct action type self-operated regulating valve; the command operation type self-operated regulating valve.
The 1.2 principle
1) self-operated pressure regulator valve working principle. The valve before the pressure P1 after the throttle valve core, valve seat, valve into the pressure P2. P2 membrane interior through the line input on the role of the top plate, the reaction force and the spring balance, determines the relative position of the valve core, valve seat, the pressure control valve. As P2 increases, the force P2 acting on the top plate also increased. At this point, the top plate is greater than the force of the reaction force of the spring, so that the valve is close to the seat. At this time, between the spool and the valve seat to reduce the circulation area, flow resistance increases, P2 decreases, until the top plate and the spring reaction force on the balance date, so that the reduced set value P2. Similarly, when the P2 is lowered. Direction and the opposite effect, the working principle of this is after the pressure regulator valve.
2) substantive work principle of the valve before the pressure regulator and pressure regulator valve working principle, should pay attention to the installation.
The difference between 1.3 Self-pressure regulating valve and control valve
Differences between these two kinds of products, is the main control valve not only need external energy (such as power or gas) drive, also need to accept foreign control instrument signal to change the valve closure member relative position, so as to realize the change of fluid flow. While the Self-pressure regulating valve is without external energy, and there is no need to accept foreign control instrument signal, pressure signal by the medium being transferred, can realize the pressure regulator.
2 self-operated pressure control valve
Because the Self-pressure regulating valve without external driving energy. Therefore, the operating force is small, it has the following characteristics.
1) balance valve structure, such as the balance of single seater. Dual core balancing type, balance type sleeve.
2) quick opening flow characteristics, its core is a flat type.
3) nominal diameter and valve characteristics: DN20~100mm (or 125). Valve is provided with a corrugated pipe, valve single-seat (some manufacturers products DN20mm no bellows, the valve core is single-seat); nominal diameter greater than 100mm. The valve cover is not provided with corrugated pipe, valve is a dual spool and sleeve structure.
4) actuator type: recommended setting value ≤ 0.6MPa, selected film type executing mechanism; setting value >0.6MPa, choose the cylinder actuator.
3 installation methods
3.1 straight pipe set
Self-pressure regulating valve, should be kept straight sections of certain (usually 6D (diameter).). The valve before the pressure from the valve of the distance should be greater than 2D; the valve after the pressure should be greater than 6D. In front of the valve, is provided with a pressure gauge, pressure gauge should be close to the pressure point, so that the set value and pressure value of true unity.
3.2 bypass system settings
Can continue to run in order to ensure the maintenance and failure of production, installation of the best bypass system.
The 3.3 filter settings
The system of the filter in the process medium clean, no impurities in the circumstances, can be omitted.
When the impurities or control valve self-operated pressure device with a command of the medium should be installed in the filter, to prevent the blocking pressure guiding pipe or command device, clamping cylinder actuator and valve etc..
If limited to pipeline installation space or budget, can filter installed in the upstream valve cut-off valve. Replace filter.
3.4 installation mode and medium, temperature
1) Self-pressure regulating valve installation should be adopted in principle, gas medium upright installation (actuator in the valve, in), liquid and steam medium inversion.
2) gas temperature higher than 70 ℃ below 140 ℃, the liquid medium temperature is higher than 140 ℃, Self-pressure regulating valve in addition
The flip, but also in the pressure pipeline for the installation of the isolation tank, and should in pressure pipeline, tank, the membrane head is filled with refrigerant, to prevent the diaphragm by high temperature aging.
3) gas temperature higher than 70 ℃ below 140 ℃. If still using upright installation, should be in the design documents (equipment) marked by high temperature membrane (such as ethylene propylene rubber diaphragm, silicone rubber membrane), otherwise it will cause the common diaphragm aging.
4, application and matters needing attention
Application and 4.1 application note
Self-operated pressure control valve is mainly suitable for no corrosion and low viscosity liquid, gas, steam (the highest temperature is 300~350 ℃), medium pressure control. Such as light oil, water, steam, air, etc.. With the valve selection should pay attention to the following situation in design conditions. Copyright dedecms
1) the valve before the valve after the pressure set value, and conditions should be close to the actual conditions of the.
Self-pressure regulating requirements on the conditions of the valve than the general control valve to strict. The process parameters are determined, not allowed to change a wide range of. As allowed by the products of the setting value adjustment range is small. General direct action valve setting value allowable deviation is ± 8%, a device with a command operation type regulating valve setting value of allowable deviation ± 4%. If it exceeds the allowed adjustable to set the spring pressure value, in order to achieve the original setting requirements, must through changing the setting spring approach can achieve the required, back to the factory to complete.
2) the permissible pressure, should pay attention to the product allows the pressure difference of the characteristics of small. This is because of the small output force and bellows and allows the pressure difference is small, allowing the pressure difference is the common control valve is small, and can not like ordinary control valve can improve the supply pressure to increase the pressure difference. Especially in small diameter of the pressure difference between the larger.
Table 1 allowable voltage difference comparison table
DN/mm1520254050
P (direct action type pressure regulating valve) /MPa
1.61.61.61.61.6
P (ZJHP fine small single-seat regulating valve) /MPa6.46.46.43.39
Note: Δ P allows differential pressure
3) because the self-regulating valve control accuracy is ± 5% and flow characteristics of quick opening characteristics, therefore only without external energy and adjust the quality requirements are not high. Content from dedecms
4) use the product is not in the reciprocating pump outlet pressure and flow control scheme. The scheme is one of the common methods of by-pass adjustment method. In this scheme, we should pay attention to the pressure control loop should not be "by direct action type (self -) pressure regulating valve". This is because the control valve to ensure the normal work of self-operated pressure, to determine the process parameters of the product requirements, are not allowed to have a larger range of variation. If used for reciprocating pump, the output flow reciprocating pump is periodic pulsation, causing the valve near the set point in a cyclical fluctuation, so as not to stabilize the pressure, so that the whole control system is not working properly. The above analysis, self-operated valve control valve for reciprocating pump outlet for pressure relief control is feasible scheme. The valve near the set point in a cyclical fluctuation, the pump outlet pressure does not exceed the set pressure value. The scheme has been implemented in Shanghai refinery canned stand used for many years.
Application and 4.2 special media attention
Application of 4.2.1 high viscosity medium
From the Self-pressure regulating the principle and structural characteristics of valve. The product can be used in the occasions of high viscosity medium, should be considered from the following two aspects.
1) regulated effect of medium viscosity on actuator - pressure guiding pipe, director, film. In order to avoid the impact of this, can be taken in a pressure guiding pipe installed on the isolation tank, filled with liquid separation, in order to make the viscous medium without clogging pressure guiding pipe and into the execution mechanism, transmission effect of modulated medium force.
2) regulated effect of medium viscosity on the trim and balance components - bellows.
This is because the modulated medium flows through the valve parts, will be introduced to balance the pressure element - bellows inside and outside, viscosity is too high will make it impossible to play the role of pressure balance. If the medium in suspension after solidification will also make the corrugated pipe cannot be started in the normal work after.
The above analysis, in the final analysis is to define the problem of medium viscosity values. At present, the recommended value of domestic manufacturing factory product samples.
The existing foreign manufacturers recommend, in oil and liquid condition, allowing the medium viscosity using 600mPa • S; medium viscosity Samson allows for 100mPa • s (density 0.8). Only when the above two requirements are met, you can use. It had been many instances. If the valve Shanghai Wo in manufacturing the products Limited production, has been in Shanghai petrochemical factory farm B focal hydraulic control (viscosity is 190mPa • S), fuel oil, heavy oil of Yanan refinery pressure control (viscosity is 135mPa • s) used for years.
The use of high viscosity medium is 4.2.2
Application of gas medium 4.2.3 does not allow leakage.
Do not allow the gas leakage of medium used, for security reasons and to avoid the waste of precious gas factors, consideration should be given to the following two points.
1) packing and other sealing joints performance standards.
The products should meet the national standard GB/T4123-92 pneumatic valve without leakage phenomenon, this point with the general requirements of control valve.
2) pneumatic actuator chamber sealing requirements to ensure no leakage. Dedecms.com
The product requirements than GB/T4123-92 high, does not allow leakage. Because the GB/T4123-92 standard to the gas chamber sealing stipulates: "the pneumatic actuator chamber shall ensure the tightness. At the rated pressure, thin film gas indoor 5min pressure drop shall not be greater than 2.5kPa; "this product in China in view of no unified product standard, it requires the use of a lot of products on the request is not strict or not to consider the gas medium, only according to GB/T4123-92 production, the production safety or saving the precious raw material adverse. This product is not suitable for the liquefied gas pressure reducing, if want to use, discusses in detail the needs and manufacturing factory.
4.2.4 use should be treated in the corrosive media occasions
Self-pressure regulating valve used in the corrosive media occasions, with the use of the higher viscosity of the occasion, the need for double take from the medium on the corrosion resistance of the implementing agencies and regulatory mechanism of two parts, can be used only when both of them meet. Therefore, it is more complicated than the control valve requirements, the use of more narrow.
For use in corrosive media occasions to facilitate the design personnel, the implementation mechanism and regulation mechanism of corrosion current materials are presented in Table 2, for reference.
In order to balanced bellows type valve for example, because of the current domestic corrugated pipe corrosion resistant materials can achieve 304 and 316. Only from the adjusting mechanism is selected, it will not be able to use in chlorine, sodium hypochlorite, chlorine, chromic acid, hydrochloric acid, sulfuric acid, zinc chloride medium. Increase the use of limitations.
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