Preheating of vacuum pump before starting
The vacuum pump for transporting hot petroleum products shall be preheated evenly before starting. Preheating can be accomplished by circulating hot oil through a pump, and the temperature of the pump shell shall not be 40 ? lower than the working temperature of petroleum products. The cracking feed pump, on average, should be preheated for about 8 hours.
If the vacuum pump is preheated unevenly, it will occur: (1) the deflection of the vacuum unit and the distortion of the shaft; (2) the cracks on the pump housing; (3) the rotating parts of the rotor are stuck.
During the circulation of hot oil, there should be no dead angle in the vacuum pump, especially in the lower part of the pump casing, where the cold oil products will gather; otherwise, the upper part of the pump casing will be hotter than the lower part. Hot petroleum products shall be free to circulate along the entire surface of the pump casing.
In fact, the measurement proves that when the temperature difference between the lower shell wall and the upper shell wall of the outer pump shell is 180 ?, the distortion of the outer bearing relative to the pump center line is equal to 5mm; in this case, the distance between the bearing centers is equal to 2m.
In order to prevent the rotor from being stuck due to temperature expansion of parts in axial and radial directions, sufficient axial and radial clearance (axial clearance of 4-7mm) shall be reserved.
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