Maintenance knowledge of Centrifugal pump
First, before installation
1.We’d better coated with a suitable rust inhibitor on the centrifugal pump surface which has not been installed and used to prevent the pump is oxidized ;
2. Bearing maintenance of its oil lubrication, we’d better be filled with a suitable fluid. However, these oil selection also has a lot of skill. For example: During use, preferably filled with a grease, rather than going to use those mixed grease. Because the life of the mechanical mixing grease has a great harm.
Second, hold down
During the centrifugal pump use, such as for special reasons (annual leave) to suspend production, resulting in long-term hold pump, then we should note in the storage process:
1. The media in the pump should be rinse with water to ensure that no residue cavity, prevent deterioration and other causes liquid mixed fluid medium;
2. The centrifugal pump must be stored in those clean environments, and extremely dry place, otherwise, it is prone to rust liquid, liquid injection and corrosion inside the pump casing structure.
Special note: If not stored properly, may cause permanent and irreparable harm, so that will has a great impact on our future use.
In actual use, there may be more questions, if you want to learn more about the centrifugal knowledge, welcome to call for free advice, with your support we can do better.
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Specific method of centrifugal pump filled with water and exhaust
The pipe section outside the pump outlet is the pressure pipe section. The pressure pipe section is equipped with a pressure gauge to measure the pump outlet pressure. The ball check valve is used to prevent liquid backflow in the water pipe section. Generally every time before pumping the pump must be filled with water, commonly known as water diversion. In addition. A drain should also be installed to direct the leaked water from the packing lid to the drain. Sometimes, for the need for anti-vibration, the pump at the entrance of the general selection of K-ST-type flexible rubber joints. Because the centrifugal pump is the impeller to pump the water out of the pump after the formation of a vacuum and water, so in addition to the impeller immersed in water centrifugal pump and self-priming pump, the valve used to adjust the size of the flow. In addition, installed in the heating, air conditioning system on the pump also need to install the thermometer. Panda water pump there are two ways: First, directly to the pump water (at this time should open the vent hole drain pump air); Second, the pump gas to go, to establish a certain degree of vacuum (at this time to close the outlet Gate valve), the introduction of water to go. The following describes several centrifugal pump water and gas exhaust method.
1.With hand pressure pump water. Some pumps come with hand pressure pumps and can also be purchased or self-made small hand pump installed in the inlet must be installed gate valve. After the valve closed, first with a small amount of water filled with water pressure machine for water, and other hand pump after the water, said the pump has been filled with water, you can boot work.
2.The use of vacuum equipment exhaust water. Centrifugal pump from the exhaust and vacuum pump pumping negative pressure exhaust is the same reason, so the use of water ring vacuum pump exhaust to achieve the role of water.
3.Filled with water in the inlet and outlet installed valve . This method is installed a valve in the water pipe, connected to the water pipe to the pump filled with water.
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Balance measures of Single-stage centrifugal pump impeller
1.Use double-suction impeller to make the axial force offset each other.
2.Open the balance hole or install the balance tube.
In the impeller on the rear cover of the impeller population to open a few counterbalancing holes, so that the front and rear cover space, while in the back cover of the axial side of the additional seal ring, the diameter and impeller inlet ring diameter the same. This structure is simple, but an increase of internal leakage, but also make imports more turbulent flow, lower single-stage centrifugal pump efficiency. Open balance hole is still 10% -25% of the axial force from the bearing to bear. You can also install the balance tube, from the rear cover near the pump casing openings, the balance pipe connected to the single stage centrifugal pump suction chamber.
3.Use balanced blades, leaves the back of a few additional radial blades, rotating, the impeller back pressure will be reduced to reduce the axial force.
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The relationship between performance requirements, flow and head of pumps
1.Pump flow and head of the curve should be no hump running stability curve, from rated flow to zero flow of the lift is rising, the value does not exceed the rated flow of 20%.
2.Pumps in the long-term continuous operation under maximum conditions. Water pump in the design conditions of the parameters to ensure that the maximum operating conditions and flow to ensure that the head.
3.Vertical centrifugal pump in a variety of operating conditions should ensure that the impeller does not occur cavitation phenomenon.
4.Critical speed of the pump For rigid rotors, the pump’s first critical speed should not be less than 125% of the maximum operating speed.
5.Horizontal centrifugal pump rotor and its main rotating parts should be static and dynamic balance test. Static balance accuracy of not less than GB9239 in the G6.3 level, dynamic balance accuracy of not less than GB9239 in the G2.5 level.
6.Abnormal vibration should not occur at any speed within the normal operating range.
7.The pump set is designed by the supplier and provides complete pump information to the purchaser.
8.Centrifugal pumps are provided with removable end caps to allow access to the internal components without moving the motor or the inlet and outlet pipes.
9.Pump inlet and outlet can withstand the stress of the pipeline may be generated without deformation. The allowable range of thrust and torque applied to the pump interface by the power plant piping is provided by the supplier.
10.All impellers shall be made of one integral casting.
11.Pump seal should be easy to disassemble, and can effectively prevent too much leakage between the pressure level to ensure high efficiency.
12.Base can withstand the weight of each component and the power of transmission.
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Vibration Analysis of Centrifugal Pump
- The centrifugal pump rotor unbalance and misalignment. This problem centrifugal pump vibration problems in a larger proportion, about 80 per cent. Centrifugal rotor unbalance factors: material to prevent uneven parts substandard, resulting in mass of the rotor shaft centerline do not coincide with the center line of eccentricity according unbalanced formation. Centrifugal pump rotor unbalance correction can be divided into two. Static and Dynamic Balancing: balance and generally referred to as single-sided double-sided balance. The difference is this: on one side is balanced by correcting the balance in a positive school, while the balance is in two-sided surface correction correction.
- Install Reason: loose foundation bolts, level of school transfer is not adjusted before the centrifugal work, to check its foundation bolts are loose phenomenon, as well as the installation of a centrifugal pump is horizontal. These conditions can also cause the occurrence of centrifugal vibration at work.
- Aforeign body in the centrifugal pump. Before centrifugal pump, the internal pump to check the next, due to the long-term use, there may be some weeds such as water and other foreign matter inside the centrifugal pump.
- Due to prolonged use of centrifugal pump cavitation caused by perforation.
- The presence of the unreasonable design , such as part sizes and other issues. However, this situation is relatively small. Centrifugal pump at the factory, in the workshop will be multiple internal testing work to ensure that the passing rate of the factory Centrifugal Pump.
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Matters need attention when use centrifugal pump
Centrifugal pump is a vane pump, relying on rotating impeller during rotation, due to the interaction between the blades and the liquid leaves the mechanical energy transmitted to the liquid, the liquid can increase the pressure to achieve the purpose of transmission fluid. Centrifugal pump starting need pay attention to four points:
1.Head at a certain speed centrifugal pump produced under a defined value. Flow and shaft power operating point depending on the unit system connected to the pump case (difference, the pressure difference and line losses). Lift with the flow rate changes.
2.Stable, continuous delivery, flow and pressure pulsation.
3.Generally no self-absorption capacity, the need to pump the liquid filled or evacuated after pipeline to start.
4.Centrifugal valve in the discharge line to start off, vortex flow and axial pumps in the valve is fully open state to start to reduce the starting power.
Because centrifugal impeller centrifugal force is formed by vacuum suction to lift the water, so that when the centrifugal pump starts, you must first close the valve, irrigation. Water level exceeds the portion above the impeller, centrifugal pump exhaust air before you start. After starting to form around the impeller vacuum to suck up the water, which can automatically open the valve, the water lifted. Thus, the valve must be closed.
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How to regulate the flow of centrifugal pump
(1)Change the opening of the valve
Change the valve switch on the centrifugal pump outlet line, and its essence is to change the pipeline characteristic curve. As shown below, when the valve off hours, increased local resistance line, pipeline characteristic curve steepens, the operating point move by the M M1, flow from the QM reduced to QM1. When the valve is opened wide, the line resistance is reduced, the pipeline characteristic curve becomes flatter, the operating point moves to M2, the flow increased to QM2.
Valves regulate the flow quickly and easily, and traffic can be continuously changed, suitable for continuous production of chemical characteristics. It is widely used. The disadvantage is that the valve off hours, increase the resistance loss, increased energy consumption, very economical.
(2) Change the speed of the pump
Change pump speed substantially change the pump characteristic curve. The original pump speed n, operating point M, as shown below, if the pump speed increased to n1, the pump characteristic curve H – Q move up, move the operating point by the M M1, increased flow from the QM to QM1. If the pump speed falls n2, the operating point moves to M2, flow down to QM2.
This adjustment method requires expensive transmission gear or the prime mover, and it is difficult to achieve continuous adjustment of flow, so rarely used in chemical production.
So it is important to use centrifugal pump correctly.
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Various losses of centrifugal pump
(1) volume loss
Losses due to leakage caused by the pump referred to volume loss. When no volume loss of power when the pump and the pump volume loss ratio of the power called pump volumetric efficiency.
(2) hydraulic losses
Fluid flow through the impeller, the pump housing, there is a change of flow rate and inverse pressure gradient magnitude and direction of the circulation and cause vortex, resulting in energy loss, this loss is called hydraulic losses. Rated flow centrifugal pump hydraulic efficiency generally 0.8 to 0.9.
(3) mechanical loss
And the bearing friction loss, seal, etc. of high-speed rotating mechanical friction between the impeller and the liquid called mechanical losses caused.mechanical efficiency is generally 0.96 to 0.99.
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