Chemical Centrifugal Pump FAQ (2-2)
81. What is radial clearance?
A: The maximum amount of activity in the radial direction is called the radial clearance.
82. What is the axial clearance?
A: The maximum amount of activity along the axial direction is called the axial clearance.
83. What kinds of clearance can be divided into?
A: According to the state of the bearing, the clearance can be divided into the following three types: original clearance, installation clearance, and working clearance.
84. What is the inspection method for radial clearance?
This method is dedicated to single row radial ball bearings.
(1) check with a feeler gauge;
(2) check with a dial gauge.
85. What are the common faults of rolling bearings?
The bearing turns blue or black;
The support heats up too fast;
There is abnormal noise during operation;
The rolling elements are severely worn;
There is a pit in the raceway;
There are cracks in the inner and outer rings of the bearing;
Bearing metal peeling off;
The rolling elements are crushed and appear in the thrust bearing;
After the installation, the hand does not move;
The bearing raceway produces scratches.
86. What are the methods for measuring the clearance of a centrifugal pump?
Pressure lead wire method;
Bar inspection method;
Lifting axis method;
87. How to measure the back interference of the bearing?
A: The measurement method of the back interference of the bearing is the lead wire method and the measuring method.
88. What is the technical standard for repairing the labyrinth seal oil ring of centrifugal pump?
A: Check the sealing teeth of all levels, there should be no defects such as dirt, rust, burrs, cracks, bends, notch deformation and breakage. Seal damage and gap should be replaced when there is excessive gap. There should be no loose or too tight after sealing assembly, seal The tip of the tooth should be sharp.
89. When repairing a centrifugal pump, what technical standards should the impeller meet?
The bushing outer garden, the balance disk hub bounce shall not be greater than 0.08mm;
Impeller seal ring, hub, bearing end face, balance disk hub axial runout should be less than 0.10mm;
The impeller and the shaft are matched by H7/h6.
If necessary, the impeller should find a static balance.
90. What are the precautions when disassembling the chemical pump?
First, the correct disassembly;
The second is the cleaning, inspection, repair or replacement of parts;
Third, it is carefully assembled according to technical requirements;
The fourth is the relative position between the components after assembly and the reasonable adjustment of the gap between the components.
91. Why is the centrifugal pump pumped out?
A: There is no pump before the centrifugal pump starts, the air is ingested, the liquid is not full or the medium is vaporized a lot. This is the centrifugal pump outlet pressure which drops sharply and fluctuates drastically. This phenomenon is called evacuation.
92. Where is the centrifugal pump pumping out?
A: The performance is that the outlet pressure tends to zero or close to the inlet pressure of the pump. The friction pair of the contact parts in the pump and the mechanical seal is worn out due to dry friction or semi-dry friction.
93. How to prevent the centrifugal pump from being pumped out in mechanical terms?
A: In terms of machinery, it is mainly to do a good job of sealing management. It is strictly forbidden to let air enter the medium from pipelines and pumps. Strictly check the static and dynamic seals during maintenance to prevent leakage due to equipment.
94. Why does the liquid in the centrifugal pump vaporize?
A: When the centrifugal pump is running, the liquid pressure drops along the pump inlet to the impeller inlet. At the K point near the inlet of the vane, the liquid pressure pK is the lowest. Thereafter, as the impeller works on the liquid, the liquid pressure rises rapidly. When the pressure near the impeller vane inlet is less than the saturated vapor pressure at the liquid delivery temperature, the liquid vaporizes.
95. What are the factors related to the centrifugal pump evaporation?
A: It has a relationship with the liquid and the pump itself. It is related to the saturated vapor pressure and vapor pressure of the medium at the current temperature, and also related to the cavitation allowance of the pump. The higher the saturated vapor pressure, the easier the medium is to vaporize. The greater the amount of erosion, the less easily the liquid vaporizes.
96. What is the reason for the high current of the centrifugal pump motor?
The relative density and viscosity of the process medium exceed the index;
When the pump starts, the outlet valve is fully open, and the resistance in the outlet pipe is too small;
The balance tube is not smooth;
The pump is not assembled properly, and the static and dynamic parts are rubbed or stuck.
97. What is the NPSH of the centrifugal pump?
A: NPSH is the abbreviation of Net Positive Suction Head. It is literally translated as a net positive suction head. It is customary in China to be called cavitation allowance. He refers to the energy of the liquid at the impeller inlet (relative to the reference surface) that exceeds the saturated vapor pressure at that temperature, as determined by the pump installation conditions. Expressed in the form of a water head. The unit is m.
98. What is the reason for the operation of the centrifugal pump?
Air in the pump or in the liquid medium;
Insufficient suction head;
Blockage of the inlet and outlet pipes;
Foreign matter in the impeller;
Liquid viscosity exceeds design specifications;
Mouth ring wear;
The prime mover is not spinning enough.
99. What are the obvious failures of centrifugal pumps?
The pump cannot be started or the starting load is large;
The pump does not drain;
The pump is interrupted after draining;
The head is not enough;
High power consumption during operation;
Pump vibration or abnormal sound;
The shaft seal is hot;
The rotor is turbulent;
A water hammer has occurred.
100. How to measure the sliding bearing clearance by the lifting shaft method?
A: Place the journal on the lower tile of the bearing, place a thousand gauge on the journal, and then lift the shaft to contact with the upper tile. The dial gauge difference is the bearing clearance.
101, What is the general content of the centrifugal pump minor repair?
Check the mechanical seal and clean the orifice plate on the rinse line;
Check the bearing and clean the bearing housing;
Eliminate leakage defects such as pump inlet and outlet lines, valves, flanges, etc.
102. What is the criteria for the rejection of ball bearings?
Two raceway washers are stripped and severely worn.
The ball is broken or has pitting.
The cage is severely deformed and cannot be folded.
103. What is the criteria for the rejection of thrust bearings?
The thrust pad is severely worn, and its thickness is reduced by 1/2 or more;
When the thrust pad is melted;
The thrust pad is unshelled and cracked.
104, How to measure the clearance of rolling bearings with a feeler gauge?
A: Confirm the maximum load position of the rolling bearing. Insert the feeler gauge between the rolling element and the outer (inner) ring that is 180°. The thickness of the elastic feeler is the radial clearance of the bearing. This method is widely used for self-aligning bearings and cylindrical roller bearings.
105, How to check the clearance of rolling bearings with a dial gauge?
A: Use a dial gauge to check, first zero the dial gauge, then push up the outer ring of the rolling bearing. The dial gauge reading is the radial clearance of the bearing.
106. How to check the rolling bearing when repairing the centrifugal pump?
There shall be no spots, holes, dents, flaking or peeling on the surface of the rolling elements and raceways;
The rotation is flexible, it should be stable after turning by hand, and gradually stop, can not stop suddenly, can not have vibration;
The isolation frame and the inner and outer rings should have a certain gap, and the hand can be used to push the isolation frame test in the radial direction;
The clearance is suitable and meets the requirements.
107. What are the contents of the hydraulic turbine repair?
Including minor repairs;
Check and replace the mechanical seal assembly;
Check and clean the mechanical seal flushing water line, check valve and inlet filter.
108. From the equipment analysis, how to extend the operating cycle of the single-stage centrifugal pump?
The dimensional and geometric tolerances of each part should be minimized.
Bearing clearance control is appropriate.
The amount of mechanical seal compression should not be too large.
The accuracy of the alignment should be improved.
The spare pump is regularly driven.
109. What are the factors that affect the vibration value of the centrifugal pump?
A: Working conditions, load, assembly, alignment, foundation and takeover, pipeline stress, process operation.