For the use of submersible pumps, we are mainly drainage, then I believe that many of the control of the water output and water flow are not understood, and then explain the various adjustment methods of the water flow control of the submersible pump.
1. Variable speed adjustment. Changing the speed of the submersible pump can change the performance of the pump, thus changing the operating point of the pump. This method is called variable speed mediation.
2. Reducer adjustment. After the impeller is turned, the performance of the pump will change according to a certain law, so that the operating point of the pump changes. The method by which the turning impeller changes the operating point of the pump is called the variable diameter adjustment.
3. Variable angle adjustment. Changing the installation angle of the blade can change the performance of the pump to achieve the purpose of changing the operating point of the submersible pump. This way of changing the operating point is called the variable angle adjustment of the pump.
4. Throttling adjustment. For the water pump device in which the gate valve is installed in the outlet pipe, when the gate valve is closed for a small time and the local resistance is increased in the pipeline, the pipeline characteristic curve becomes steep, and the operating point moves to the upper left along the Q-H curve of the water pump. The smaller the gate valve is closed, the greater the increased resistance and the smaller the flow. This method of changing the operating point of the pump by closing the small gate valve is called throttle regulation or variable valve regulation.
When the small gate valve is closed, the local head loss of the pipeline increases, the pipeline system characteristic curve moves to the upper left, and the pump operating point also moves to the upper left. The smaller the gate valve is closed, the greater the local head loss and the smaller the flow rate. It can be seen that the throttling adjustment not only increases the local head loss, but also reduces the amount of water, which is uneconomical. However, due to its simplicity and ease of use, it is widely used in small water pump devices and pump performance tests.
Pumps are general-purpose mechanical products. China’s pump products have approximately 450 series and more than 5,000 specifications. They are widely used in agriculture and water conservancy, construction industry, petroleum industry, power industry, shipbuilding industry, mining, metallurgical industry and environmental protection industries. . In recent years, with the rapid growth of the domestic economy, the market’s demand for pump products has also grown rapidly. According to statistics from the Industrial Pump Research Institute of Zhejiang University of Technology, the sales revenue of the pump industry in China exceeded RMB 100 billion in 2009, and the industrial output value of the industry was around RMB 108 billion, with a balance between production and sales. The regional industrial output value of the industry is: 26 billion yuan in Wenling, Taizhou, 10 billion yuan in Wenzhou Yongjia, 5 billion in Hangzhou, 15 billion in Shanghai, 6 billion in Shandong, 8 billion in Shenyang, and Dalian 6 billion yuan, 5 billion yuan in Guangzhou, 3 billion yuan in Beijing Tianjin, 2.5 billion yuan in Shijiazhuang, and Changsha 25 In recent years, the pump industry has maintained a momentum of rapid growth. In 2007, the growth rate was 23.20%, but due to global finance Affected by the economic crisis, the growth rate of the industry in 2008 has dropped slightly, to 13.5%. With the rapid development of the pump industry and the fierce market competition, the growth rate of the pump industry will tend to be stable, and it is expected that the future.
The five-year industry development rate is between 13% and 17%. The industry’s development focus will shift from quantitative growth to quality improvement.
(1)Improve the centrifugal pump suction port to the impeller near the structural design. Increase the flow area; increase the radius of curvature of the inlet section of the impeller cover, reduce the rapid acceleration and decrease of the liquid flow; reduce the thickness of the inlet of the blade, and make the leaf inlet rounded so that it is close to the streamline, Reduce the speed of the blade around the blade and increase the surface of the impeller and the blade surface to reduce the loss of resistance;
(2)Use pre-induction wheel, so that the flow in the pre-induction wheel in advance to work to improve the flow pressure.
(3)Use double suction impeller, so that the flow from the impeller on both sides of the same time into the impeller, the import cross-section doubled, the import flow rate can be reduced by double.
(4)The design of the use of slightly larger positive angle to increase the blade inlet angle, reduce the blade at the entrance of the bend, reduce the blade blockage to increase the import area; improve the working conditions under high flow to reduce Flow loss. But the angle should not be too large, otherwise the impact of efficiency.
(5)Use anti-cavitation materials. Practice shows that the higher the strength, hardness and toughness of the material, the better the chemical stability and the stronger the resistance to cavitation.
Multistage centrifugal pumps should be placed as far as possible in a well ventilated place to facilitate rapid cooling and reduce motor temperature. Otherwise, run for a long time, easy to burn the motor.
If the use of multi-stage centrifugal pump, because did not remove the plastic film covered in the motor, causing the motor overheating, burn the coil. In addition, before starting, be sure to check the water inside the pump, otherwise, not only affect the self-priming performance, and easy to burn the shaft seal parts. Under normal circumstances, multi-stage centrifugal pump starts after 3 to 5 minutes that should be out of water, or should immediately stop inspection.
When the multi-stage centrifugal pump once a failure, avoid their own hands. Because of their own demolition, I do not know where the fault caused by blindly split a pass; Second, no special tools and often damage the original good parts. The best way is to have experienced, large-scale maintenance point repair, and timely replacement of “overage” parts and some wearing parts. Under normal circumstances, multi-stage centrifugal pump should be repaired once every six months, put an end to “sick” work.
First,multi-stage centrifugal pump outlet pipe resistance is too large; pump direction of rotation; multi-stage pump impeller flow blockage or damage, pump speed is insufficient.
Second, check or shorten the horizontal multi-stage pump outlet pipe to eliminate dirt or replace the impeller impeller; check the pump motor, increase the pump speed.
The use of low-temperature submersible pumps is mainly used in oil and chemical plants to transport liquid hydrocarbons, liquefied natural gas and liquid nitrogen and liquid liquefied gas in refrigeration systems. Therefore, it is also called cryogenic pump.
The installation of the cryogenic pump and the operation of the cryogenic pump are:
1) cryogenic pump assembly parts are strictly prohibited with water and grease, parts must be washed with a solvent clean, dry and then assembled.
2) not only the cryogenic pump itself to be cold, low temperature pump suction line must also have cold measures to prevent the heat in the operation from the outside, so that the liquid vaporization, affecting the performance of the pump.
3) If there is oil, moisture and air in the cryogenic pump and piping, it will freeze when it enters the cryogenic liquid, so it needs to be cleaned before the cryogenic pump is put into operation and then scavenged with dry nitrogen. Pump the water and air, and pre-cooling.
4) The suction port and the suction pipe of the cryogenic pump should have the exhaust device so that the pump can remove the gradually accumulated gas before and during the operation to ensure the reliable operation of the cryogenic pump.
5) In the case of explosive gas, the motor should use vertical explosion-proof motor.
6) low temperature transmission can also use low temperature shielding pump or stainless steel magnetic pump.
(1) Small pump seal failure below 715kW often produce grinding shaft, grinding shaft position mainly in the following: dynamic ring auxiliary seal, static ring position, a few springs have grinding axis phenomenon.
(2) The main reasons of grinding: ① BIA-type double-ended mechanical seal, back pressure state is a bad working condition, the media particles, impurities are easy to enter the sealing surface, so that the seal failure. ② The main part of the grinding shaft is rubber bellows, and because the upper sealing surface is in bad lubrication state, the friction torque between the static and dynamic ring is larger than the transmission torque between the rubber bellows and the shaft, and the relative rotation occurs. ③ Dynamic and static ring auxiliary seal due to the sewage in the weak acid, weak alkali corrosion, rubber pieces have been inelastic. Some have rotten, lost the proper function, resulting in the phenomenon of grinding shaft.
(3) To solve the above problems, now take the following measures: ① to ensure that the lower end of the cover, the cleanliness of the oil chamber, not clean the oil prohibited assembly. ② machine oil chamber oil tank line should be higher than the static and dynamic ring sealing surface. ③ according to the use of different media use different structure of the machine seal. For high-lift pump should be re-designed mechanical seal structure, the corrosive media rubber should be selected weak acid, weak alkali of fluorine rubber. Seal ring should be added to the ring.
Pumps are widely used in power, chemical, metallurgy, petroleum, agriculture and other sectors of the national economy, is the energy onsumption of large, annual power consumption of the pump accounts for about 1/5 of the total power generation. Therefore, it is very important to improve the safety and economy of the pumps in various production systems. Rapid diagnosis of pump failure, reasonable maintenance of equipment, and constantly improve the operation of the pump in the system effect is engaged in pump equipment design, installation and maintenance of engineering and technical personnel common goal.
In recent years, there are some weak links in the field of pump maintenance, the quality of work and work efficiency are inadequate, the main reason is that a large number of mechanical engineering graduates in the years after graduation, the work is done and maintenance, And engineering students in the school almost no maintenance of equipment in the field of formal training; industrial production in the actual repair business, more by the experienced but no academic engineers or workers to deal with these people also lack the basic training of various basic training , So can not carry out a high level of maintenance work; pump maintenance project managers have received high engineering education, generally only from the instructions to engage in repair, and equipment designers generally lack the use of experience, but also from the user feedback is less, So the development of the pump maintenance instructions are not necessarily reasonable.
When the centrifugal pump is running, the outlet valve can not be closed for a long time.
When the centrifugal pump outlet valve closed is not closed, if the flow is too small, only the efficiency of centrifugal pump will drop, waste electricity, no effect on the centrifugal pump equipment. Once the closure of the valve is too small to a certain limit, will lead to centrifugal pump noise and vibration increases, the performance of the centrifugal pump will appear unstable phenomenon. And the centrifugal pump valve closed in the case of long-term operation will lead to the pump inside the liquid temperature rise, once the centrifugal pump is running in a closed state of small flow or no flow operation, the water pump in the pump through the role of high-speed rotation Water in the pump chamber in the rapid cycle and the pump friction, will lead to a sharp rise in pump temperature, the export pressure will rise, if the pump temperature is too high or even lead to the risk of pump burst, the motor current will rise, The current can also cause the motor to burn out of the fault. So the centrifugal pump can not turn off the outlet valve for a long time.
Since the direction of the suction pipe and the outlet pipe is affected by the rotation direction of the stainless steel multi-stage centrifugal pump, it is important to understand the definition of the rotation direction. The stainless steel multistage centrifugal pump centrifugal lift is constant for a given impeller diameter and flow, and the lift head is a function of flow. At some point on the head flow curve, once the lift head exceeds the centrifugal head, then at these points Pressure gradient reverse, resulting in the opposite direction of flow, that is, the phenomenon of reflow.
The mechanism of the inlet return of the impeller with low specific speed centrifugal pump is analyzed from the theoretical and experimental aspects. It is considered that the rotational speed component is the main reason for the inlet return of the impeller, and it is pointed out that the return flow is the main reason leading to the instability of the small flow. As the design staff in the design of low-speed high-speed induction wheel stainless steel multi-stage centrifugal pump is often used positive angle method, in order to ensure that the induction wheel produced stainless steel multi-stage centrifugal pump head to meet the energy requirements of centrifugal wheel imports, The inlet angle is greater than the liquid flow angle, and the centrifugal wheel is given better cavitation performance, and the blade inlet angle is larger than the liquid flow angle. In order to obtain high efficiency, in the design of ultra low specific speed high speed induction wheel centrifugal pump When the actual flow angle is smaller than the flow angle under the design conditions, so that the induction wheel and the centrifugal wheel inlet front has a non-uniform peripheral velocity component, Thereby producing a vortex around the flow line.
Therefore, the inlet return of the stainless steel multistage centrifugal pump induction wheel and the centrifugal wheel is actually caused by the uneven velocity of the liquid flow at the edge of the rotating blade, which is a vortex that involves the vortex and the vortex around the axis flow.