【Haichuan Construction Technology】Do you know why the pumps in a system need to be rotated? How to operate it?

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I. What is \"cranking\" of equipment? It refers to the process of rotating the shaft of a pump or other rotating equipment several times by hand or using a cranking device before starting the motor. This is done to determine whether there is any sticking or increased resistance in the mechanical or transmission components, thereby preventing the motor from being overloaded and damaged during startup. II. Core purposes of turning the machine: 1. Prevent equipment from getting stuck: Avoid situations where, after the unit stops operating, high-temperature components such as bearings and bearing shells may bend or get stuck due to temperature differences, or where the lubricating oil may solidify and stick together. 2. Check for potential hazards: By manually rotating the components, inspect key parts such as the rotor and gears for any signs of jamming, unusual noises, or looseness, in order to prevent mechanical failures in advance. 3. Protection sealing/lubrication: Turning the shaft before starting up allows the lubricating oil to cover the bearing surfaces and sealing surfaces evenly, forming an oil film that prevents dry friction and equipment damage at the moment of startup. 4. The purpose of turning the hot oil pump by hand is to ensure even heating and cooling of the pump’s upper, lower, left, and right parts, as well as to check whether the pump shaft has bent or deformed. Especially in centrifugal pumps used for high-viscosity media, the medium inside the pump causes the impeller and the pump casing to stick together. Starting the motor without first rotating it will result in an excessive starting load that exceeds the motor’s rated current, thereby damaging the motor. 5. The barring of large-scale units is carried out for warming up and lubrication before startup, in order to prevent localized overheating of the rotor and the casing after startup, which could lead to thermal deformation. (1) To prevent thermal deformation, a pump that has just been stopped generally needs to be cooled for a short period of time (30 minutes) before its shaft is turned. 2(2) For units that have been out of service for an extended period, it is necessary to rotate the shaft regularly to prevent bending or deformation of the shaft, as well as to avoid jamming of the pump rotor due to the transfer of media with high viscosity; generally, the shaft should be rotated 540 degrees in each direction. III. Methods of turning the shaft (taking the main pump/compressor in a vacuum distillation unit as an example) 1. Manual shaft turning (mandatory after shutdown/before startup) ① Shaft turning before equipment startup: For pumps with interlocked start-up, set the motor’s interlock switch to the manual mode to prevent the pump from starting automatically during shaft turning, which could cause injury. ②Turn on the wheel housing switch to open the wheel housing. Ensure that the pump is in standby mode; use your hand (for small pumps) or a crank lever (for large and medium-sized pumps) to turn the pump at its coupling position, usually for at least one and a half turns, before starting it up. Slowly turn the wheel with both hands, following the normal rotation direction of the steering wheel; turn it at least 1.5 full turns (540°) each time, and check for any resistance or unusual noises. After turning the shaft, close the coupling cover, lock the safety pin, and record the shaft rotation time and condition. ③Regular turning of the standby equipment: Since some pumps transport media with high viscosity or containing particles, this can cause sticking and blockages in the equipment’s rotors, hence regular turning is necessary. Of course, for equipment that is parked for long periods of time, especially those with relatively long pump shafts, it is necessary to perform regular shaft turning to prevent the shaft from bending. The number of degrees turned in each rotation should be an odd multiple of 180 degrees (red on odd days, white on even days) in order to correct any bending in the shaft. (Since the centrifugal pump rotor has its own weight, gravity causes the rotor to bend to a certain extent. By rotating the rotor 180°, the direction of the rotor shaft’s bending is reversed compared to before rotation, thereby achieving automatic correction of the rotor’s alignment.) ) 2. Electric barring method 1 (commonly used for large-scale units, for periodic barring after shutdown) ① Confirm that the unit’s lubrication oil system is operational, with the oil pressure and temperature within the specified ranges. ②Switch to the \"electric barring\" mode and start the barring motor; the unit will rotate slowly at a very low speed (usually 1-5 r/min). ③ Check the barring gear status regularly (e.g., every 30 minutes); before shutting down the machine, stop the barring gear motor first, and then cut off the lubrication system. 3. Electric barring method 2 (for large units such as compressors): ① The worm gear and gear reduction mechanism of the barring device converts the rotation generated by the barring motor into the rotation of the crankshaft, thereby enabling barreling. ②Before starting the machine, it is necessary to turn the shaft in order to push the small piston to its extreme rear position. To unlock the shaft turning handle, it must be pulled outward from the shaft turning cover and then adjusted to the shaft turning position; at this point, the rotation of the shaft turning handle causes the pinion to slide axially inward to its extreme position, allowing it to mesh with the gear. Once the shaft turning motor is started, shaft turning can be carried out ； At this time, since the pressure oil acting on the pressure regulation controller is connected to the drain port of the handle box, it ensures that the contacts of the pressure regulation controller open, preventing the main motor from starting. ③The crank device can rotate the shaft in both forward and reverse directions; this can be achieved by moving the control lever to the corresponding crank position. It must be noted that whether turning the machine over or starting it up, the oil pump motor needs to be started first.