Nominal pressure - the nominal value of the technical parameter of various equipment , pumps , heat exchangers , pressure vessels , pipelines , fittings , etc. Any product has specific dimensions, justified by strength calculations . The calculations take into account the materials selected for the manufacture with the characteristics of their strength at 20 ° C of the working medium, which ensures a given equipment life at a certain working pressure of the medium. This pressure is called nominal (conditional) pressure.
For many technical devices, this parameter is most important due to the fact that it determines the strength characteristics of the equipment, the possibility of its interfacing with the connecting parts of various pipelines, the ability to standardize the requirements for testing conditions for the strength and density of materials and compounds.
Content
Standards and Rules
The definitions of this parameter, as well as its specific values, are established by various state rules and standards approved in a particular country. In Russia, it is also known in technical documentation , literature, catalogs as conditional pressure, which is explained by the fact that this term was renamed in 1986 in connection with the release of new GOSTs to bring the designation to international standards. Initially, the new standards retained the Py designation as an alternative to the new PN designation (also used by the Pnom designation), these designations were used to mark technical products. However, from January 1, 2011, this alternative in the standards regarding the use of the obsolete designation ( Py ) was excluded . Thus, the only true designation for nominal pressure is PN at this time .
Examples of established standards and rules
Nominal pressure (in a hydraulic actuator , pneumatic actuator and lubrication systems ) is the highest overpressure at which the device must operate for a specified resource (service life) while maintaining parameters within the established norms. [one]
Nominal pressure (in water supply and sewage systems ) is a constant internal overpressure of water, which pipes and fittings can withstand for the entire life cycle (50 years) at a water temperature of 20 ° C. [2]
The concept of nominal pressure is used according to GOST 26349-84 for valves and connecting parts of pipelines , such as flanges , bends , tees , etc., the same standard sets specific values for the nominal (conditional) pressures used in this area.
A number of nominal pressures in the hydraulic drive , pneumatic drive and lubrication systems are established by GOST 12445-80.
In the "Rules for the design and safe operation of vessels operating under pressure (PB 03-576-03)" [3], the following terms are defined:
- Test pressure - the pressure at which the vessel is tested.
- Working pressure - maximum internal overpressure or external pressure that occurs during the normal course of the working process.
- Design pressure - the pressure at which the strength is calculated.
- Conditional pressure - design pressure at a temperature of 20 ° C, used when calculating the strength of standard vessels (assemblies, parts, fittings).
Nominal Pressure Range
When designing a hydraulic actuator, the nominal pressure in the hydraulic system is assigned in accordance with the normal range of pressures according to GOST 6540-68 and GOST 12445-80 (MPa): 0.63; 1.0; 1.6; 2.5; 6.3; ten; sixteen; 20; 25; 32. For pipeline valves (ball valves, wedge and slide valves) and pipeline components (tees, couplings, transitions, elbows, bends, etc.), are assigned in accordance with the normal range of pressures according to GOST 356-80 (MPa): 0 ,ten; 0.16; 0.25; 0.40; 0.63; 1.00; 1.60; 2.50; 4.00; 6.30; 10.00; 12.50; 16.00; 20.00; 25.00; 32.00; 40.00; 50.00; 63.00; 80.00; 100.00; 160.00; 250.00.
Notes
- ↑ GOST 12445-80. Volumetric hydraulic drives, pneumatic drives and lubrication systems. A series of basic parameters.
- ↑ SP 40-102-2000.
- ↑ approved by the resolution of the Gosgortekhnadzor of the Russian Federation No. 91 of June 11, 2003