Export throttle. For low and medium ratio pump, this is the most common and low flow regulation method. This method is usually limited to use on a low and medium ratio pump. Partial closing of any valve on the outlet pipe will increase the pressure head of the system, so the pressure head curve of the system will intersect with the head curve of the pipeline pump at a smaller flow rate. The outlet throttle moves the operating point to a lower efficiency point and has a power loss at the throttle valve. This may be important for large pump devices, and the high investment regulation may be more economically attractive. The throttle close to the dead may cause the fluid to overheat in the pump, and can use the bypass to maintain the necessary minimum flow, or use different means of regulation. This is very important for the pumps mentioned earlier in the treatment of hot water or volatile liquids.
2. inhalation throttling
If sufficient NPSH is available, some power can be saved by throttling in the suction line. Because the outlet throttle can cause overheating or vaporization of the liquid, the jet engine fuel pipe pump often uses inlet throttling. Under very small traffic volume, the impeller of these pumps is only partially filled with liquid. Therefore, when the input power and temperature rise are about the outlet throttling, the flow of 1/30 condensate pump which is sufficiently transposition of the impeller is usually controlled by submerged depth to 7, which is equivalent to inlet throttling. Special designs can reduce the cavitation damage of these pumps to a degree of insignificance, but the energy levels are also low.
3. bypass adjustment
The discharge line from the pipe pump can be divided into all or part of the flow, through the bypass pipe to the suction port or other appropriate point of the pump. One or more flow orifice plates and appropriate control valves can be installed in the bypass. The metering bypass is usually used to reduce the flow of the boiler feed pump, mainly in order to prevent overheating. If the excess flow of the bypass paddle pump is used to replace the outlet throttle, considerable power can be saved.
4. speed regulation
When the flow is adjusted by this method, the required power can be minimized and the overheating in the flow regulation process can be eliminated. The steam turbine and the internal combustion engine are easily adapted to the speed regulation at a very small additional cost. All kinds of mechanical, magnetic, hydraulic transmission and DC and AC variable speed motors can all be used to adjust the speed. Usually, the variable speed motor is too expensive. It is proved that it is worthwhile to use adjustable blade adjustment when the special case is studied economically.
After studying the adjustable guide vane installed in the front of the impeller, it is found that this method is effective for the regulation of the pump when the number is =5700 (2.086). The blade produces a positive prespin to reduce the pressure head, flow rate and efficiency. In addition, a relatively small regulation effect is obtained only from the blade. The large energy storage pumps used in Europe for power generation have successfully applied the adjustable exit diffuser blades. The propeller pump with variable pitch blades is also successfully studied. In the case of constant pressure head and relatively small efficiency loss, a larger flow range can be obtained. But these methods are too complex and expensive, so they are very limited in practical applications.
5. gas supplement
Gas supplement to the suction port of the pipe pump is also a method of regulating the flow rate, which can save some power compared to the outlet throttling. Usually, we do not want to have air in the conveying liquid, and too much air always causes the pump to lose the risk of its perfusion head. So this method is seldom applied in practice except for some occasions.
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