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I. Fill-in-the-blank questions: 1. The main steps for introducing circulating water to the coolers in the urea plant: turn on the coolers’ ( ) and ( ), and introduce water； Water coming out of the exhaust valve confirms that the equipment is filled ； Turn on the cooling water ( ). 2. What are the operational differences between high-speed centrifugal pumps and ordinary centrifugal pumps? When starting a high-speed centrifugal pump, the outlet valve must be ( ) before the pump is started. When stopping the pump, the outlet valve should not be ( ) yet; the pump should be stopped first, and then the outlet valve closed to protect ( ) ； Generally, before starting a centrifugal pump, ( ) should be closed; after it starts, the outlet valve should be opened slowly. When stopping the pump, the outlet valve should be closed first, and then ( ). 3. If cavitation occurs in the pump during operation, it is necessary to check whether the inlet liquid level is ( ) ； Is there ( ) in the inlet pipeline? Are there any issues with the inlet valve? ； Are there any ( ) areas in the inlet pipeline? ； Is the liquid level ( ) too high? ； Should the inlet ( ) be cleaned? ； For viscous media, it is necessary to check whether low temperatures increase resistance. 4. The reason why the motor cannot be started and stopped repeatedly is that a large current is generated when the motor starts, ( ) times ； The coil burns out from continuous operation ； Generally, consecutive startups of more than ( ) are not allowed. 5. The method for evacuating a centrifugal pump is: inlet ( ) ； Stop and restart ； Entrance ( ). 6. The deterioration of lubricating oil is manifested by the oil turning into ( ), and if water gets into it, it will turn into ( ) ; other properties of the oil also change. 7. Steps to start a centrifugal pump: Shut off the pump ( ) and the flushing water valve, check the oil quality and level, and turn the pump shaft by hand ； Slowly open the inlet valve of the pump, and start it up for operation ( ) ； Open the ( ) of the pump and check its operation. 8. The contents of the five fixations and three filtrations are: Five fixations: regularity, ( ), fixed time, ( ), fixed quantity. Three filters: pour from the large barrel into the fixed container (), pour from the white porcelain barrel into the hand oil pitcher, and pour from the hand oil pitcher into the () fuel filling point. II. Short-answer questions: 1. What is the working principle of a centrifugal pump? 2. Describe the operations for warming up the turbine pipes and the machine? 3. How to flush a high-pressure system? 4. What are the requirements to start the high-pressure ammonium methoxide pump? III. Draw the P102 ammonia system flow diagram