[Q&A Question 165] 2016.10.02
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【Q&A Question 165】October 02, 2016: Why is a time limit specified for rotating the reciprocating engine’s crankshaft? How long should the rotation generally last? The answer key will be available after responding; scoring is based on addressing the key points. Answer: The cranking time is generally 5 minutes. The main purpose of cranking is to check that the transmission components of the compressor are functioning properly. If the cranking time is too short, problems won’t be revealed; if it’s too long, a lubricating film cannot be formed, and the moving parts end up grinding dry.
The cranking time is generally 5 minutes. The main purpose of cranking is to check that the compressor’s driving components are functioning properly. If the cranking time is too short, problems won’t be revealed; if it’s too long, a lubricating film cannot be formed, and the moving parts end up grinding dry.
For the reciprocating machines here, we turn them by hand before starting them up after maintenance, and it takes 2 or 3 minutes. Spare reciprocating machines are generally not turned by hand due to the pressure present. Switch at any time
Within 2 hours after parking, 4 times per hour； Within 2-4 hours after parking, 2 times per hour ； Within 4-6 hours after parking, once per hour. During the unit’s barring operation (that is, within 6 hours after shutdown), the lubricating oil system remains operational, and the interlock system activated by a slight drop in oil pressure is engaged to prevent dry grinding.
At lower speeds, in order to prevent the rotor shaft from bending due to uneven heating, a barring gear must be used. When the turbine is shut down, a barring gear or manual operation of the barring gear is also necessary to prevent the rotor shaft from bending under its own weight. For turning the turbine while it is hot, four hours should be specified; when it is cold, 2–4 hours are required.
The purpose of cranking the engine is to check whether the piston gets stuck during its stroke, thereby preventing the rotor from bending. Generally, just spin a few times, 180°
Reasons for rotating the reciprocating engine’s crankshaft at regular intervals: Prolonged shutdowns – Before shutting down the engine, use the oil injector manually to supply an adequate amount of lubricant to the cylinder bores and packing. Thereafter, it is also necessary to use the oil injector regularly (once a week is recommended) to lubricate the cylinders and packing, as well as to rotate the crankshaft several times. This prevents the crankshaft from deforming due to lack of movement over time, and it ensures that lubricant reaches all the lubrication points, thereby preventing corrosion； Turn the machine to check the standby status of the reciprocating machine. Turning time: For units of 500KW and below, each turning takes about 10 minutes ； For units of 500KW and above, the turning operation should be carried out for about 20 minutes each time ； The interval between each time should not exceed one week.