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3-2 Types and performance comparison of hydraulic pumps P386
Pumps can be divided into fixed displacement type and variable displacement type according to performance . If classified according to structure, it can be divided into four types : gear pump, screw pump, vane pump and piston pump ( see Table 3-1) .
3-2-1 gear pumps (Gear Pump) P387
The gear pump may be divided into an external gear pump (external gear pump) and the internal gear pump (Internal Gear Pump) .
( 1 ) External
gear pump
2. Oscillating internal gear pump
3-2-2 screw pump (Screw Pump , screw pump, IMO P UMP ) P390 the
The screw pump is composed of two or more rotors with similar thread shapes . This pump can rotate at high speed and has very low noise. It can be used in submarines, elevators and other occasions that need to be quiet.
Characteristics of screw pump
(1) Continuous discharge, less pulsation and less pressure fluctuation.
(2) The tooth shape is large, it can bear larger load impact, and the reliability is high.
(3) The relative speed of the inner and outer rotors is small, with less wear and long life.
(4) Can rotate at high speed.
(5) Low vibration and low noise.
3-2-3 vane pump (Vane Pump) P392
( 1 ) Fixed displacement vane pump
Unbalanced vane pump
Balanced vane
( 2 ) Compound Pump (Combination Pump) or high and low pressure pump P394
( Three ) the variable displacement vane pump (Variable Displacement Vane Pump) P394
The advantages of the variable displacement vane pump are as follows:
1. Provide the oil quantity required by the circuit correctly. If the circuit pressure reaches the set value, the output oil quantity is almost equal to zero.
2. No remaining hydraulic oil flows back to the oil tank through the drain valve, so there is less power loss and less oil temperature rise, improving efficiency.
3. No matter linear motion or rotary motion, it can achieve stepless speed change.
n3-2-4 Piston Pump P397
The piston pump is a high-pressure, high-efficiency pump, and the volumetric efficiency can reach 95 ~ 98% . Among all hydraulic pumps, piston pumps can provide maximum power density
( 1 ) Axial type inclined shaft piston pump P397
( 2 ) Axial swash plate piston pump P399
( 3 ) Radial type fixed cylinder piston pump P401
n When the flow rate of hydraulic oil increases, a low-pressure area will be formed, and the gas dissolved in the hydraulic oil will escape to form bubbles and generate some voids. When these voids flow to the high-pressure area, they will be suddenly compressed to produce local ultra-high pressure and knock Abnormal vibration and noise occur on the surface of the material and erode the material. This cavity phenomenon is called cavitation. The extent of cavitation will vary depending on the amount of gas dissolved in the hydraulic oil, the change in the flow rate of the hydraulic oil, and the viscosity of the hydraulic oil.
n Cavitation corrosion of the pump will reduce the efficiency and discharge volume . The best way to prevent cavitation is to prevent the pump from sucking in air , reduce the resistance of the filter and improve the suction capacity of the pump .
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3-5 Matters needing attention when selecting hydraulic pump P404
( 1 ) Pressure
of hydraulic
pump (Pressure)
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( 2 ) Flow and flow rate of hydraulic pump
the range of hydraulic pump sizes is very wide. The smaller ones, such as missiles, use only 1 gal / min , and the larger ones, such as ships, use 2000 gal / min , depending on need.
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In general hydraulic systems, petroleum-based oils are the most widely used. However, if fire-resistant or synthetic hydraulic oils are used for safety considerations, special hydraulic pumps must be used. Even the oil seals in hydraulic pumps need to be replaced. The speed should also be reduced, otherwise the efficiency will be reduced and the pump life will be reduced.
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The pump power and the weight ratio with the use of different occasions are different, the ratio pump general industrial pound about 1/3 of Hp , about pound aircraft . 4 of Hp , up to pound on the missile . 8 of Hp , but Life expectancy is relatively reduced. As for the price, the fixed displacement pump is cheaper than the variable displacement pump of the same type, and the piston pump is more expensive than the vane pump and gear pump of the same energy.
Goto Zulie teacher teaching network gas hydraulic control practice