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Hydraulic pump

Author : Xiong Date : 9/30/2012 5:10:04 AM
Hydraulic pump

Hydraulic pump is the power of the hydraulic system components, its role is to let  the mechanical energy  of prime mover convert to be  liquid pressure energy, refers to the hydraulic system of oil pump, it provides power to the whole hydraulic system . The structure of hydraulic pump usually have a piston pump, vane pump and gear pump.

1. The classification of hydraulic pump:

According to whether the flow can be adjusted, it can be divided into: variable pump and quantitative pump.
Output flow can according to need to adjust  called variable pump, the flow can not be adjusted called quantitative pump.
According to hydraulic system in common use pump structure is divided into: piston pump, gear pump and vane pump three.

Piston pump: volumetric efficiency is high, the leakage is small, can work under high pressure, mostly used for high power hydraulic system; But complicated structure, material and machining precision demand is high, the price is expensive, the purity of the oil demand is high

Gear Pump: smaller, the structure is simple, the oil cleanliness requirements is lax, the price is cheap; But the pump shaft by unbalanced force, wear serious, large leakage.

Vane pump: divided into double action vane pump and the single-acting vane pump. This kind of pump flow even, smooth operation, low noise, pressure and volume efficiency ratio gear pump is high, the structure than the gear pump complex.

General in the gear pump and vane pump can not meet the requirements to use piston pump. There are some other forms of hydraulic pump, such as screw pump, etc., but the application as the above three kinds of common.

2. The hydraulic pump working principle:

Hydraulic pump is for hydraulic drive provide pressure liquid of a kind of hydraulic components, is a kind of pump. It is the function of the engine (such as motor and internal combustion engine, etc.) of the mechanical energy into liquid pressure energy. Diagram for single plunger pump working principle. CAM by motor to drive the rotation. When CAM promote plunger upward movement, piston and cylinder form sealing volume decreases, and oil from seal volume of extrusion, the check valve exhaust to places where they are needed. When CAM rotary to decline curve of site, spring force plunger down, forming a certain degree of vacuum, the oil in the tank under the action of atmospheric pressure into the sealing capacity. CAM make plunger constantly lifting, sealed volume periodically decrease and increase, pump have been oil suction and discharge.

3. The advantages and disadvantages of hydraulic pump and application:

Piston pump (hydraulic motor) due to constitute a seal work cavity member - plunger and cylinder block bore are cylindrical surface, processing is convenient, easy to get higher fit precision, good sealing, the volumetric efficiency is high, high working pressure. At the same time this kind of pump as long as change plunger stroke can be very convenient to change its flow, easy to realize variable. Therefore piston pump in high pressure and large flow, high power hydraulic system and flow need adjustment occasions, such as gantry planer, broaching machine, hydraulic press, engineering machinery, mining machinery, shipping machinery and so on widely used.

Piston pump (hydraulic motor) according to the plunger arrangement way and the direction of motion is different, can be divided into axial plunger pump (hydraulic motor) and radial plunger pump (hydraulic motor) two kinds big. Axial plunger pump has the advantage of compact structure, radial of small size, light weight, moment of inertia small and easy to realize variable, high pressure (40 mpa or higher), can work under high pressure in high speed, and has high volumetric efficiency. So the pump in the high pressure system is widely applied. Not enough is the pump to oil pollution is very sensitive, general need fine filter. At the same time, this pump self-priming ability is poor, often need by low pressure

Gear pump is the main advantages of simple structure, small volume, light quality, manufacturability good, the price is cheap, self-priming capability is strong, is not sensitive to oil pollution, speed range is big, easy maintenance, reliable work. Its defect is trapped oil phenomenon is serious, the radial unbalance force is big, leakage, pulsation of the flow rate, noise is higher, can't do variable pump use. Low pressure pump is widely used in low pressure (25 x 105 pa below) of the hydraulic system, such as machine tools and various oil compensating, lubrication and cooling device, etc. Pump on the structure to take certain measures, also can achieve higher working pressure. Medium pressure pump is mainly used in machine tool steel rolling equipment hydraulic system. In high pressure and high pressure pump is mainly used in agriculture and forestry machinery, engineering machinery, shipping machinery and aviation technology.

And gear pump, gear motor due to poor sealing, volumetric efficiency is low, so the input oil too much, so does not produce large torque and rotational speed and torque are as gear meshing condition and pulsating. Gear hydraulic motor used in high speed low torque hydraulic system. Gear pump is generally can be directly used for hydraulic motor, i.e., the gear pump and gear hydraulic motor both is reversible.

And gear pump, compared to vane pump flow even, smooth operation, low noise, long life, small dimensions, structure is compact etc, but there is also self-priming ability is poor, speed range of small, maximum rotational speed is low, leaf easy to bite dead, work reliability is bad, the structure is complex, more sensitive to oil pollution shortcomings and so on. So in the work environment is polluted, speed range changes greatly machinery on the application of relatively less. In the work reliability requirement of high places, such as plane, also rarely used. Vane pump in, low pressure hydraulic system especially in machine tool industry in most applications. Including single-acting vane pump often do use variable pump, the rated pressure low (6.3 MPa), often used in combination machine tools, pressure machinery, etc.; Double-acting vane pump can only do quantitative pump use, its rated pressure can reach 14 mpa - 21 mpa, in all kinds of machine tools (especially precision machine tool) equipment, such as injection molding machine, transportation loading and unloading machinery and engineering machinery and other medium voltage system widely used. Blade hydraulic motor the biggest advantage is small in volume, inertia small, action is sensitive, allowing the reversing frequency is very high, or even in a few milliseconds reversing. But its biggest weakness is leakage is bigger, mechanical properties is soft, not in lower speed, speed range not great. Therefore suitable for low torque, high speed and the requirements of inertia small, the mechanical property requirements is lax occasions. Due to the variable vane hydraulic motor structure is relatively complicated, and relative motion of parts, leakage is bigger, volumetric efficiency is low, the mechanical properties of soft and regulate the inconvenience, and other factors, the blade hydraulic motor is generally made quantitative type, i.e. general vane hydraulic motor is double-acting quantitative hydraulic motor.

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