How to "break vacuum emergency stop"?
First, pump efficiency diagram
How much do you know about the efficiency of vacuum pumps? Where did the loss go? How to improve pump efficiency... 5 aspects, comprehensive analysis!
vacuum coating machine,pvd coating machine,pvd vacuum machine,vacuum ion coating machine,multi-arc ion coating machine
Second, the three aspects of energy loss in the pump
The pump is a kind of energy conversion machine. The energy conversion process is bound to be accompanied by the loss of energy. The efficiency is the measure of this conversion. How to improve the efficiency of the pump and reduce the loss of energy? It is necessary to understand the loss of energy in the pump. The energy loss in the pump mainly includes the following three aspects:
1. Mechanical loss
Mainly the friction loss of the liquid and the outer surface of the front and rear cover of the impeller and the pump chamber (also called disc loss).
Disk losses account for a large proportion, even reaching 30% of the effective power. Tests have shown that the disk loss is proportional to the cube of the rotational speed and proportional to the fifth power of the outer diameter of the impeller.
Therefore, the larger the outer diameter of the impeller, the greater the disc loss. Although the disk loss is proportional to the cube of the rotational speed, the outer diameter of the impeller is correspondingly reduced with a given head, and the outer diameter of the impeller is correspondingly reduced (it can be considered that the pump speed is doubled and the outer diameter of the impeller is reduced by half). The disc loss decreases in proportion to the fifth power. Therefore, as the rotational speed increases, the disc loss does not increase, but decreases, which is one of the reasons for the development of high-speed pumps.
2, volume loss
A part of the liquid of the impeller leaks back to the impeller inlet through the gap of the impeller seal ring and cannot be effectively utilized to form a loss. Therefore, the gap of the seal ring should be as small as possible, but due to processing and assembly, too small gap may form eccentric wear or jam. The national standard specifies the gaps of various types of pumps.
3. Hydraulic loss
The fluid in the flow-through portion (from the inlet to the outlet) of the pump must have losses due to changes in the speed and direction, both of which are hydraulic losses. To reduce this loss, in addition to improving the smoothness of the overcurrent components, try to use an excellent hydraulic model.
How much do you know about the efficiency of vacuum pumps? Where did the loss go? How to improve pump efficiency... 5 aspects, comprehensive analysis!
Third, the pump efficiency formula analysis
What is the efficiency of the pump? What is the formula?
Answer: Refers to the ratio of the effective power of the pump to the shaft power. η = Pe / P pump power usually refers to the input power, that is, the power transmitted by the prime mover to the pump shaft, so it is also called the shaft power, denoted by P.
vacuum coating machine,pvd coating machine,pvd vacuum machine,vacuum ion coating machine,multi-arc ion coating machine
The effective power is the product of the pump head and mass flow and gravity acceleration.
Pe=ρg QH (W) or Pe=γQH/1000 (KW)
ρ: density of pumped liquid (kg/m3)
γ: the weight of the pump to deliver liquid γ = ρg (N / m3)
g: gravitational acceleration (m/s)
Mass flow Qm=ρQ (t/h or kg/s)
Fourth, the general method of improving pump efficiency
Improve the piping system and reduce drag. The length of the pipeline should be shortened and kept as straight as possible, reducing the flow rate to reduce head loss along the path; reducing the number of components such as gate valves, bottom valves, elbows, orifice plates, etc., to reduce local head loss.
The fulfilment of reducing the water pressure of the pump is just as appropriate to meet the requirements of the piping system for the water pressure.
The pump is the most widely used general-purpose machine, and it is also a large consumer of power consumption. Therefore, improving the efficiency of the pump itself and the efficiency of the pump are important for saving energy.
Improve the efficiency of the pump itself:
1. The blade extends to the suction port and is thinned to make the liquid act early by the blade, which can reduce the outer diameter of the impeller, and can also increase the length of the flow line in the blade channel and reduce the relative diffusion; however, the extension should be appropriate, and the extension should be too long. The Et area is too small, so that the corner angle at which the blade inlet intersects the blade cover becomes smaller, which in turn increases the hydraulic friction loss and squeezes the inlet flow path, which is disadvantageous for cavitation and efficiency.
2. The ratio of the flow path outlet and the inlet area between adjacent blades is controlled within the range of 1.0 to 1.3 to reduce the diffusion loss. If the ratio is greater than l. 3. The flow channel is seriously diffused and the efficiency is reduced.
vacuum coating machine,pvd coating machine,pvd vacuum machine,vacuum ion coating machine,multi-arc ion coating machine
3. The larger the hydraulic radius of the runner, the better. Make the blade inlet section close to the square as much as possible to reduce the friction loss. It is known from hydraulics that the ratio of the cross-sectional area of the cross-water to the wet-week is called the hydraulic radius, that is, the hydraulic radius-water cross section. Area / wet week. The wet circumference is actually a large contact area between the liquid and the wall. When the cross section of the flow passage is changed from an approximately square to a narrow rectangle, the liquid is substantially allowed to flow through the gap of the narrow section, so the resistance is inevitably large.
4. Due to the large hydraulic loss of the curved diffuser, most of the diffused sections with a slightly curved line approaching a straight line are now used. For the anti-guide vane, its inlet angle and its position in the circumferential direction should be combined with the flow of the liquid flow in the diffusing section. The principle is to form a continuous flow passage to avoid the cross section of the anti-guide vane inlet passage being too narrow. Otherwise eddy currents and impact losses can occur at the inlet of the anti-guide vanes.
5. For multi-stage pumps, the impeller inlet is pre-rotated (the anti-guide vane exit angle is less than 90.), reducing the relative speed of the impeller inlet and reducing the relative velocity diffusion. When the anti-guide vane exit angle is selected to be less than 90. When the water flows into the impeller, a pre-rotation occurs. 1≠0.
6. The pre-rotation caused by the exit angle of the anti-guide vane has a great influence on the characteristics of the lower impeller. In the design, in order to make the theoretical lift formula Ht-U2Vu2 "1Vul in the lVul, the anti-guide vane The exit angle should be chosen to be 90. This eliminates the rotational component for the final guide vanes. However, experiments have shown that this is unfavorable for efficiency and obtaining a stable performance curve. Especially for some low specific speed pumps, in order to obtain a decreasing characteristic curve, the exit angle of the antivanes should be less than 90 degrees, usually between 60 and 80 degrees. . Both ends of the blade are thinner to avoid impact and eddy current losses.
Section of the blade runner:
7. Increase the width of the impeller outlet and reduce the absolute speed of the impeller outlet, thereby reducing the hydraulic loss in the pressurized water chamber.
8. Obliquely cut the impeller outlet, reduce the length difference between the front and rear flow lines or different flow lines to select different blade exit angles in order to reduce the pressure difference between the front and rear cover flow lines, thereby reducing the secondary backflow of the outlet.
9. Increase the throat area of the pressurized water chamber. When the original design area is small, the flow can be blocked.
Reduce mechanical and friction losses
1 The mechanical friction loss caused by bearings and packing is generally small, and has little effect on efficiency. The mechanical friction loss of the packing seal is larger than that of the mechanical seal, and it is better to use the mechanical seal shell 4.
2 Improve the smoothness of the surface of the impeller and the guide vane. If possible, it is best to use a hand-held grinding wheel to polish the surface of the runner so that the hydraulic friction loss is significantly reduced.
3 The friction loss of the front and rear cover surfaces of the impeller and the disk generated by the liquid is proportional to the 5th power of the outer diameter of the impeller. Selecting a larger blade exit angle reduces the outer diameter of the impeller, thereby reducing disc friction losses. The disc friction loss is related to the surface roughness, and the outer wall of the impeller cover should be as smooth as possible. Appropriately reducing the gap between the impeller cover and the vanes can also reduce the disc friction loss.
Reduce leakage:
Appropriately reduce the gap of each part or lengthen the seal gap and use the labyrinth seal to increase the leakage resistance to reduce the volume loss.
Leakage in the pump occurs at the impeller and seal ring, between the multi-stage pump stages, and the axial force balance device.
Improve pump efficiency:
Improve the piping system and reduce drag. The length of the pipeline should be shortened and kept as straight as possible, reducing the flow rate to reduce head loss along the path; reducing the number of components such as gate valves, bottom valves, elbows, orifice plates, etc., to reduce local head loss.
The fulfilment of reducing the water pressure of the pump is just as appropriate to meet the requirements of the piping system for the water pressure. If the richness of the pump pressure is too large, the water pressure of the pump is higher than the pressure required by the system, which is necessary to reduce the pressure by using a small valve and other throttling methods, resulting in wasted power.
vacuum coating machine,pvd coating machine,pvd vacuum machine,vacuum ion coating machine,multi-arc ion coating machine
At this time, the pump must be modified. The first and second stage impellers can be removed according to the pressure required by the system. If the excess pressure is not too large, the turning impeller method can be used to decompress the pump, so that the pump in the system (pipe) device works as much as possible. At the optimum efficiency point of the pump, avoid working at high or low flow rates (lower efficiency points).
5. Other factors affecting pump efficiency and solutions
Other factors that affect the efficiency of centrifugal pumps:
1. The efficiency of the pump itself is the most fundamental impact. For pumps under the same working conditions, the efficiency may differ by more than 15%.
2. The operating condition of the centrifugal pump is lower than the rated working condition of the pump, the pump efficiency is low, and the energy consumption is high.
3. The efficiency of the motor remains basically unchanged during operation. Therefore, it is important to choose a high-efficiency motor.
4. The impact of mechanical efficiency is mainly related to design and manufacturing quality. After the pump is selected, the post management impact is small.
5. Hydraulic losses include hydraulic friction and local resistance loss. After the pump is running for a certain period of time, the surface of the impeller and the vane and the like are inevitably worn, the hydraulic loss is increased, and the hydraulic efficiency is lowered.
6. The volume loss of the pump is also called leakage loss, including three leakage losses of the impeller seal ring, the interstage, and the axial force balance mechanism. The volumetric efficiency is not only related to design and manufacturing, but also related to post management. After the pump is continuously operated for a certain period of time, the gap is increased due to friction between the components, and the volumetric efficiency is lowered.
7. The centrifugal pump is evacuated and idling due to blockage of the filter cylinder, intake of the pipeline, and the like.
^^^^^^^^^^
8. Before the pump starts, the staff does not pay attention to the preparation work before the start of the centrifugal pump. The basic operating procedures such as the warm pump, the disc pump and the pump are not performed thoroughly, which often causes the cavitation phenomenon of the pump, causing the pump to have large noise, large vibration and pump efficiency. low.
Measures to improve the efficiency of the centrifugal pump:
1. Replace the inefficient centrifugal pump. When replacing, use a centrifugal pump that is close to the actual operating conditions to ensure that the replaced pump is always operating at high efficiency. After replacing the inefficient and high-consumption centrifugal pump, the pump efficiency can be increased by about 10%.
2. Application of frequency conversion energy-saving technology. For centrifugal pumps with design parameters greater than the actual operating conditions, after installing the variable frequency speed control device, it always runs in the high efficiency zone.
3. Promote the application of new energy-saving products such as high-efficiency and energy-saving permanent magnet speed regulating motors and dual power motors on the main centrifugal pumps.
4. When selecting a new pump, the pump produced by a large manufacturer should be selected to ensure high efficiency of the centrifugal pump.
5. Maintenance of the centrifugal pump.
(1) Always check and adjust the centrifugal pump shaft end seal to reduce the volume loss;
(2) When the centrifugal pump has been running for 10,000 hours, it should be overhauled to restore the pump efficiency;
(3) Promote the application of bellows sealing technology on the centrifugal pump to completely eliminate the leakage of the centrifugal pump and improve the volumetric efficiency.
6. Regularly clean the filter cylinder, check the pipeline connection, and ensure that the centrifugal pump inlet pipe is unblocked.
7. Strictly follow the operating rules of the centrifugal pump. Before starting the pump, the disc pump should be opened, the inlet valve should be opened, the outlet valve should be closed, and the exhaust gas should be vented to check whether the inlet pressure of the pump meets the requirements. Prevent cavitation of the pump due to low supply pressure and insufficient flow.
8. Regularly check the pump efficiency of the centrifugal pump. For the pump set with low pump efficiency, it is necessary to find the cause in time and take corresponding measures to solve it.