【Q&A Question 098】April 08, 2017
Thread Content
【Q&A Question 098】April 08, 2017: Why is it specified that the time taken for cranking a reciprocating compressor should not be too short nor too long? (Unless otherwise specified, all questions and answers are based on hydrogenation units.) ) The reference answers will be visible after responding; points are awarded by identifying the key points. Too short a barring time may fail to reveal problems, and it also prevents the oil film from covering the bearings evenly ； Excessive cranking time can lead to dry friction, causing damage to the machine. 2017 Q&A Summary Thread (updates starting now) http://bbs.hcbbs.com/thread-1657793-1-1.html 2017 Daily Question Summary Thread (updates starting now) http://bbs.hcbbs.com/thread-1657794-1-1.html 2016 Q&A Summary Thread (updates completed) http://bbs.hcbbs.com/thread-1597792-1-1.html Petrochemical Sector – “Creative Ideas for Energy Saving” Campaign (Sponsors sought; highest returns ever) http://bbs.hcbbs.com/thread-1666758-1-1.html Sponsors are being sought for this campaign; those interested can contact the campaign coordinator. (Sponsors of the event are entitled to the policy allowing them to include promotional ads as sponsors in various events held in the petrochemical region for one year.) The Petrochemical Advanced Processing version – the event to share pictures of chemical equipment has started! A vast amount of wealth, as well as HCH coins, are waiting for you to claim them: http://bbs.hcbbs.com/thread-1760733-1-1.html. Notice regarding the collection of chemical engineering technical materials in the “Petroleum and Chemicals Section”: http://bbs.hcbbs.com/thread-1614796-1-1.html (Source: HCH Chemicals Forum)
Too short a time period fails to achieve the purpose of turning the shaft, while too long a time period can lead to wear
Because the lubrication oil pump is not started when the turbine is turned during standby. When the compressor is to be put into operation, the oil pump must be started first, followed by cranking the machine to provide initial lubrication to the relevant components, before starting the compressor itself.
If the turning time is too short, it may be possible to fail to detect problems, thus failing to fulfill the intended inspection purpose of turning the machine. Excessive cranking time may cause damage due to insufficient lubrication of the compressor
Answer: If the cranking time is too short, and the compressor has not completed one full rotation or has rotated only a few times, it is not possible to identify any problems, nor can a proper oil film be established in the friction pairs before the motor starts. That’s why 5 minutes is specified as the cranking time. However, too long a cranking time is also undesirable, as the compressor’s speed is quite low during cranking, and it is not possible to maintain an oil film at such low speeds for an extended period; without a consistent supply of lubricant, dry friction may occur.
Too short to provide cranking action; too long causes shaft wear
Too short prevents sufficient movement, while too long damages the seal
Insufficient oiling by the oiler, excessive time spent on shaft rotation leads to easy wear of the bearings; too short a rotation time prevents meeting the requirement of 180 degrees of rotation per day
Too short a barring time may fail to reveal problems, and it also prevents the oil film from covering the bearings evenly； Excessive cranking time can lead to dry friction, causing damage to the machine.