The working pressure and rated pressure of pneumatic high-pressure control valves directly affect its sealing performance, operating stability and safety. For applications such as oil and gas, chemical processing, hydraulic testing, and industrial automation, the purchaser must not select valves based solely on normal pressure of the pipeline, but must also take into account maximum operating pressure, temperature fluctuations, pressure surges, fluid characteristics, and system safety requirements.
As a supplier of pneumatic high-pressure control valves, before recommending products, we should first understand the actual use of pneumatic high pressure control valves. This involves determining the valve's pressure rating valve, body material, sealing structure and actuator configuration to ensure that the product meets the system's operational requirements.
I. Distinguishing Working Pressure from Pressure Rating
Before selecting a pneumatic high-pressure control valve, work pressure, rated pressure and pressure test pressure must be distinguished. While these parameters are interrelated, they are not directly interchangeable.
1.Working Pressure: refers to the pressure exerted by the medium to the valve during actual operation. Choose with an understanding of normal work pressure, maximum work pressure and potential pressure fluctuations.
2.Rated pressure: The pressure range the valve is permitted to withstand under specified conditions. Actual allowable pressure may be influenced by temperature, materials, structural design and applicable standards.
3.Pressure test pressure: refers to the pressure applied during the test to verify the integrity of the pressurized component in accordance with the relevant standards. This does not indicate that the valve is suitable for long-term operation at this pressure level.
For example, if a device has a normal working pressure of 10 MPa, the selection of a valve rated 10 MPa may not be appropriate. The the system's maximum pressure, temperature conditions, transient pressure and pressure limits specified in product standards shall also be verified.
II. Valve selection based on Maximum System Working pressure
In determining the rated pressure of the valve, priority should be given to the system's maximum possible working pressure rather than relying solely on the equipment's average operating pressure.
Specific evaluations should include the following three areas:
-Normal Operating Pressure: Determine the typical pressure range for stable operation of the system.
Maximum Working Pressure: Consider potential pressure variations during equipment startup, shutdown, load change, and process transitions. -Risk of abnormal pressure: Analyze whether factors such as water hammer, pressure pulsations or pump/compressor start/stop cycle could result in transient pressure spikes.
Valves shall be selected in such a way as to ensure that the allowable working pressure of the valve under actual operating temperature and conditions meets or exceeds the design pressure required by applicable standards, with a reasonable margin of safety.
It is important to note that safety margin are no substitute for engineering calculations. For high-pressure systems, the design pressure must be determined in accordance with applicable design specifications and risk assessments; a fixed percentage increase over normal operating pressure is not sufficient.
III. Determination of Pressure Ratings based on working temperature
The pressure bearing capacity of a pneumatic high-pressure control valve depends not only on its structural design but also on working temperature.
The strength and allowable pressurization capacity of certain metal materials may vary with temperature; sealing materials may also age, harden or become inelastic as a result of high temperature, low temperature or heat circulation.
Key considerations in selection process include:
1. Valve's allowable pressure at minimum and maximum operating temperatures.
2. valve body material is suitable for long-term working environment.
3. Compatibility of seals with process media and temperature.
4. temperature fluctuations may lead to thermal stress or poor sealing performance.
For industrial systems involving high temperature vapours, low temperature gases or frequent temperature fluctuations, suppliers should be required to provide rating parameters for these conditions, rather than relying solely on ambient temperature pressure ratings.
IV. INTRODUCTION Selection of valve body and sealing structure based on Medium Characteristics
Even if both systems have the same working pressure, the valve configuration required may vary greatly depending on the medium involved.
For example, compressed air, hydraulic oil, water, corrosive chemicals and special industrial gases have different requirements for valve body materials and sealing structures.
When selecting a pneumatic high-pressure control valve, the following factors should be considered:
-Medium corrosiveness: Valve body, plug (or trim) and seal corrosion resistance to medium.
-Moderate viscosity and cleanliness: Assess the possibility of clogging, wear or damage to movement of the plug. -Sealing requirements: choose an appropriate sealing solution according to the permitted level of leakage and leakage.
Moderate hazard: For flammable, explosive or toxic media, determine applicable safety design and certification requirements in conjunction with a systematic risk assessment.
As a supplier, product selection should be based on information provided by the customer (e.g. media name, concentration, temperature and pressure),rather than recommending products based solely on valve size and rated pressure.
Verify the compatibility of valve pressurization capability with the pneumatic actuator.
Pneumatic high-pressure control valves is generally composed of valve body and a pneumatic actuator, each performing distinct functions.
The body withstands the pressure of the medium, while the pneumatic actuator uses compressed air to generate the drive needed to open, close or modulate the valve.
Therefore, the following must be confirmed in selection:
1. Body pressurization capacity: The requirements of medium pressure, temperature and related design standards must be met.
2. Executing agency output capability: must be sufficient to overcome dielectric pressure differentials, seat loads, packing friction and other operating resistance.
3. Air supply pressure range: must conform to the actuator's design specifications, taking into account the fluctuation of field air supply.
4. Fault safety function: Determine if the valve should be closed, opened or maintained in position in the event of loss of air supply in accordance with process requirements.
It is important to note that the actuator's air supply pressure is not equal to the average working pressure of the valve. Even if the pneumatic actuator operates properly, it cannot be proved that the valve body itself is suitable for the corresponding high pressure condition.
VI. INTRODUCTION Validation of selection results through technical documentation and stress tests
After completing the initial selection, verify the product technical documentation and related test requirements to ensure that the selected valve meets actual application conditions.
The purchaser may request the supplier to provide the following information:
-Product specifications and model parameters.
-Nominal pressure and temperature ranges.
Material information for body, trim (plug/core) and seals.
-Applicable design and inspection standards.
Data from shell pressure test and seat leakage test. -Necessary material certificates, inspection reports and product certification documents.
The shell pressure test is mainly used to verify the integrity of the pressurized boundary, while seat tightness is used to assess leakage performance when the valve is closed; the purpose of the two tests is different. Test pressure, test medium, retention time and allowable leakage rates shall be determined in accordance with applicable standards and product requirements.
For high-pressure liquid systems, testing must also take into account stored energy and risks associated with media release; testing should be conducted by qualified personnel in accordance with established safety procedures.
FAQ
1. Is the working pressure of pneumatic high-pressure control valves valve higher the better?
No. A suitable model shall be selected according to system design pressure, operating temperature, medium and control requirements. Blind selection of higher pressure levels may increase procurement costs, but do not guarantee superior control accuracy or sealing performance.
2. Can the pressure test pressure of the valve be used as its working pressure?
No. Stress test pressure is a value applied under specific test conditions and cannot be used as a long-term working pressure. Actual allowable operating pressure shall be based on product rating parameters and applicable specifications.
3. How to tell if a valve can withstand pressure surges?
It is necessary to assess the size, duration and frequency of pressure fluctuations and system structure, and to verify valve design and related test requirements. Suitability for operating conditions involving frequent pressure pulsations cannot be determined solely on the basis of static pressure ratings.
4. Does the air supply pressure of the pneumatic actuator affect the valve's pressure rating?
These are all distinct parameters. Air supply pressure mainly affects the actuator's output capability while the pressure retention ability of the medium is determined by the design and rating parameters of the valve body. However, inadequate air supply may prevent valves from opening or closing as expected.
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