(1) under what circumstances should the safety valve be calibrated
1) before long-term storage or first use
2) periodic check
3) seriously damaged and rusted valve
4) valve with lost nameplate
5) damaged valve with lead seal
(2) the adjustment significance and method of seat back pressure
National standard of the definition of back pressure refers to the relief valve to discharge, medium pressure dropped to a certain value, the disc to contact with the seat, i.e. open height is zero, the valve inlet of the static pressure, back pressure is too low, too much is bad, too low will cause medium and energy loss, is too high, short of emissions, causing the valve frequency jump, principle is in emissions to reach as far as possible under the condition of the high back pressure, reduce the medium and energy loss.
(3) adjustment method
The pressure of the return seat is adjusted through the adjusting ring. The principle of the adjustment is the clearance principle. The smaller the clearance, the greater the resistance is when the valve core is ejected.
For a safety valve with only a lower regulating ring, the regulating ring is up, the pressure of the return seat is down, the regulating ring is down, and the pressure of the return seat is up.For the safety valve with the upper and lower adjustment rings, the distance between the upper and lower adjustment rings decreases, the pressure of the return seat decreases, the distance between the upper and lower adjustment rings increases, and the pressure of the return seat increases.
(4) calibration method and its advantages and disadvantages
Safety valve check has two methods: field check (on-line check) and platform check. If possible, field check should be carried out as far as possible.
Advantages of field calibration: it is convenient to check the welded safety valve, can measure the pressure of the return seat, accurate measurement.
The disadvantage is that the calibration time is long, and the system should be repeatedly boosted, which is not economical and dangerous.
Advantages and disadvantages of safety valve normal temperature test stand:
A. to solve normal temperature and working temperature below 250 ° C of the relief valve setting and leak detection.
B. The small error range of opening pressure of the safety valve is determined, which saves the adjustment time of newly installed safety valve, reduces labor intensity, reduces energy consumption and reduces work risk.
C. There is an error between the operating temperature and the normal temperature (the spring softens at high temperature), and the pressure of the return seat cannot be checked.
(5) medium used for normal temperature calibration
Air, nitrogen and water (pressure above 20Mpa) are commonly used in normal temperature calibration.Inflammable, combustion-supporting or poisonous and harmful media such as oxygen, hydrogen and acetylene gas cannot be used as the medium source for verification.Kerosene, gasoline, diesel oil and so on cannot be the medium source.Carbon dioxide gas is non-toxic and non-combustible, but it is easy to freeze and block the pipeline.
(6) safety valve calibration principle
Enter the medium with pressure into the inlet of the inspected safety valve, and when the medium pressure rises to the open state of the safety valve, the pressure at this time can be measured, and the open pressure at the current position can be adjusted to the specified opening value to complete the check of the opening pressure.Then, when the pressure drops to the specified value (90% of the open pressure), the pressure gauge or other legal method shall be used to check whether there is any leakage of media, i.e., sealing check.