Hydraulic excavator is a kind of multifunctional machinery, which is widely used in water conservancy engineering, transportation, electric power engineering and mining excavation and other mechanical constructions. Plays a very important role. Small Digger,Mini Excavator Trailer,Mini Hydraulic Excavator,Hydraulic Mini Excavator Shandong Nuoman Engineering Machinery Co., Ltd , https://www.chinanuoman.com
1, reduce the necessary NPSH
(1) Water pump with double suction impeller. Since the NPSH Δhc of the double-suction pump is smaller than the NPSH Δhc of the single-stage single-suction pump, a double-suction impeller is used for the pump with the same speed n and flow Q.
(2) Properly increase the impeller inlet diameter and increase the blade inlet width. When the diameter of the impeller inlet and the inlet width of the blade increase, the absolute velocity and the relative velocity of the inlet of the impeller decrease, which indicates that the critical NPSH of the pump decreases. However, at this time, the area of ​​the leakage reduction ring at the inlet of the impeller is increased, the leakage amount is increased, and the volumetric efficiency of the pump is reduced.
(3) Add an inducer before the impeller. Induce the wheel before the centrifugal pump impeller. The inducer wheel and the pump leaf operate, and the generated pressure wheel is assembled together after being assembled coaxially. The pressure generated by the inducer pressurizes the inlet of the impeller to improve the anti-cavitation performance of the pump. However, adding an inducer will make the performance of the pump unstable. Therefore, further exploration and research are needed.
2, to improve the flow through anti-cavitation ability to reduce material member cavitation damage to the pump parts and prolong its service life, the choice often strong cavitation erosion resistance of materials. Such as cast manganese, bronze, stainless steel and alloy steel castings impeller; or coated with polymer or laser sprayed parts of the surface of the flow resistance to resist cavitation damage. In addition, finishing the surface of the flow-through component to improve its smoothness can also reduce the hazard of cavitation.
Measures to reduce pump cavitation 2. Improve cavitation erosion resistance of water inlet devices
The NPSH is closely related to the water inlet device and piping system. Therefore, a good water inlet device should be designed to increase the NPSH of the pump inlet as much as possible to meet the dynamic pressure drop requirement of the pump.
(1) Reasonably determine the water absorption height of the pump. Since the pumps are generally operated under non-design conditions, full consideration should be given to the various conditions that may be encountered in the operation of the pump. The determined water absorption height should meet the water pump performance requirements under any operating conditions.
(2) Match a reasonable inlet pipe. Minimize the length of the inlet pipe and unnecessary pipe accessories. Increase the diameter of the inlet pipe appropriately to reduce the hydraulic loss of the inlet pipe and increase the NPSH of the pump inlet. For large and medium-sized axial flow pumps, the distribution of water flow velocity and pressure in the inlet pipe is as uniform as possible, which will help prevent cavitation from occurring.
(3) A well-designed intake basin. A good pool entry not only reduces the landing of the water level in the pool, but also reduces the resistance coefficient of the inlet pipe, and the water surface in the pool does not generate a vortex. Air can be prevented from entering the pump, preventing cavitation from occurring prematurely.
3, the measures that can be taken in the operation management
(1) Try to make the pump run in the design condition accessory. According to the specific conditions of the pumping station, variable valve, variable speed, variable angle and other adjustment measures can be adopted to prevent the pump operating condition from deviating from the design condition.
(2) Control the actual speed of the pump higher than the designed speed. Since the NPSH must be proportional to the square of the rotation speed, when the rotation speed is too high, not only the NPSH margin must be significantly increased, but also the effective NPSH margin is reduced.
(3) When cavitation occurs during the operation of the water pump, the water pump inlet may be filled with a small amount of air or high-pressure water flow to reduce or avoid cavitation damage.
Mini Excavator,The hydraulic drive of the excavator is closely linked, and its development is mainly based on the application of hydraulic technology. Its structure is mainly composed of engine, hydraulic system, working device, walking device and electrical control. Due to the harsh working conditions of the excavator, the required action is very complicated, so it puts high requirements on the design of the hydraulic system The hydraulic system is also the most complicated in the hydraulic system of construction machinery. Therefore, the analysis and design of the hydraulic system of the excavator has become an important part of promoting the excavator. The single-bucket hydraulic excavator is a kind of mechanical equipment for periodic operation. It consists of three parts: working device, slewing device and walking device. The working device includes a moving stick and various replacement equipment that can be replaced according to the work needs, such as front shovel, backhoe, loading bucket and grab bucket. The typical working cycle is as follows: (1) Excavating hard soil, generally during excavation Mainly stick action, use bucket cylinder to adjust cutting angle, cooperate with excavation; when digging in soft soil slope, the main action is bucket cylinder; in special excavation action, use bucket cylinder , Stick cylinder and boom cylinder combined action to ensure that the bucket moves according to a specific trajectory. (2) The full bucket lift and rotary excavation are completed, the bucket cylinder is pushed out, the arm cylinder is raised, and the full bucket is lifted; at the same time, the rotary motor is started, and the rotary table rotates in the direction of unloading soil. (3) The unloading turntable is transferred to the unloading location. The turntable brake bucket rod cylinder adjusts the discharge radius. The bucket cylinder is retracted and the bucket is unloaded. When there are strict requirements on the unloading position and height, it is necessary to move the arm kr to cooperate. (4) After the unloading is completed, the turntable rotates in the reverse direction, and at the same time, the boom cylinder and the arm cylinder cooperate to move the empty bucket down to a new digging position. The single-bucket hydraulic excavator has a very wide range of applications in construction, transportation, water conservancy construction, open-pit mining and modern military engineering. It is an indispensable main mechanical equipment in various earthwork constructions.
Improve the cavitation resistance of pumps