Random Section of GOST 12.2.085-2002
3.2.3. Adjustment pressure: a maximum excessive pressure at the valve entry while the valve is closed and design tightness is maintained.
Valve adjustment pressure in case of direction to the system without backpressure is recognized equal to design pressure.
Valve adjustment pressure in case of direction to the system with backpressure is recognized less than the design backpressure.
3.2.4. Backpressure: excessive pressure on the valve output during service release.
3.3 Valve throughput capacity: weighted service flow through the valve.
3.4 Design flow area: a narrow section area of the valve seat.
3.5 Flow coefficient:
3.5.1. Flow coefficient for gaseous service: a ratio of the measured valve capacity to the capacity calculated under the same parameters through the ideal nozzle with the area of a narrow section which is equal to the design flow area of the valve.
3.5.2. Flow coefficient for liquid service: a ratio of the measured valve capacity to the capacity calculated not considering the resistances caused by a valve through the flow area equal to the valve output branch pipe area.
4. General requirements
4.1 Valves and the associated accessories that comply with GOST 12.2.063,  shall be used for vessel protection.
Vessels with possible increase of the operating pressure from the supply source, chemical reaction, heating, solar radiations in case of fire near to the vessels, etc are subject to protection by safety valves.
4.2 Number of valves, their dimensions and capacity shall be selected so that to prevent causing the vessel internal pressure exceeding the design pressure for more than 0,05MPa (0,5kg/cm2) for pressure vessels of up to 0,3MPa (3kgf/cm2), by 15% — for pressure vessels of 0,3 to 6,0MPa (3 to 60kgf/cm2) and by 10% — for pressure vessels exceeding 6,0MPa (60kgf/cm2).
It is acceptable for the vessel internal pressure to increase by not more than 25% of the design pressure provided this increase is confirmed by the strength calculation per GOST 14249, GOST 25215, GOST 26303, ST SEV 5206, effective regulatory documents, anticipated by technical documentation and stipulated in the vessel passport.
4.3 Calculation of the valve capacity is described in the Attachment A.
4.4 The structure and materials for the valve components and accessories shall be selected depending on the service parameters and properties to provide the reliable operation of the valve.
4.5 The valve structure shall provide free movement of its moving parts and shall not allow for their outbreak.
4.6 The structure of the valve and accessories shall not allow for the arbitrary change of its adjustment.
4.7 The valve structure shall not allow for unacceptable strokes during open/close movements.
4.8 Valves shall be mounted in locations that provide easy and safe maintenance and repair.
In case a valve requiring regular maintenance is located at elevation higher than 1,8m additional access platforms or other means shall be provided for safe maintenance.
4.9 For the vertical vessels the valves shall be mounted on the bottom plates, for horizontal vessels – on the top generatrix in the gaseous (vapor) phase area.
Valves shall be installed in the locations that exclude the formation of dead spaces.
4.10 Installation of shutoff valves between a vessel and a safety valve as well as downstream the safety valve is prohibited except the requirements described in 4.11.
4.11 The system of main and backup valves shall be considered for flammable and explosive substances, Class 1 and 2 substances as per the GOST 12.1.007 as well as for the vessels operating at cryogenic temperature.
4.12 The main and backup valves shall have equal capacity that provides full protection from the pressure increase. In order to ensure the valve revision and repair shutoff valves with interlocks shall be installed upstream and downstream safety valves that prevent from simultaneous closing the main and backup valves, the flow area at any position not being less the flow area of the safety valve.
4.13 Safety valves are not accepted for pressure control in the vessel or group of vessels.
A manufacturer shall supply passport and operating instructions along with valves. Passports shall contain the flow coefficients for gases and liquids as well as the corresponding flow areas.