Inspection items and quality requirements for standard nozzles of standard throttling devices of the Ministry of Electric Power:
1. The end face on the upstream side of the standard nozzle should be smooth, and its surface roughness should not be greater than 0.0003d, which is equivalent to a surface roughness of not less than 3.2.
2. The downstream end face of the nozzle should be parallel to the upstream end face, and its surface roughness can be one level lower than the upstream end face.
3. The diameter d of the cylindrical throat is the arithmetic mean of not less than 8 single measurements, of which 4 are at the beginning of the cylindrical throat, 4 are at the end, and at approximately the same angle of 45° measured at the location. The difference between any single measured value and the average value shall not exceed 0.05%.
4. The entire flow surface from the inlet plane of the nozzle to the cylindrical throat should be smooth without any visible or detectable edges or irregularities.
5. The outlet edge of the cylindrical throat should be sharp, free of burrs and visible damage, and no obvious chamfer.