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    Select the Right Hydraulic Motor for Your Applications

    What factors should be taken into consideration when selecting a hydraulic motor? The first thing that should be focused on is the operating conditions of the hydraulic system, following which we should decide on the output torque, speed and power as needed so as to pick a right product model and specification. Generally speaking, gear motors are simple-structured and priced affordably, often used under conditions where high speed and small torque are required while motion stability is not, for example, used for driving grinders, fans, etc. Vane motors stand out for small rotational inertia and quick responsiveness but their volumetric efficiency is not high and their mechanical characteristics are soft, all of which makes them suited for operating conditions of medium speed, small torque and frequent starting and commutation, to be specific, driving the table of grinding machines and launching machine tool operating systems, etc. Axial plunger motors offer prominent volumetric efficiency, wide speed range and good stability at low speed yet with relatively weak impact resistance. Motors of this type are often used in demanding high-pressure systems, for instance, serving as the major transmission for internal combustion locomotives, or playing an essential part in hoisting machinery, or used for lifting and turning construction machinery, mining machinery and ships. As to radial plunger motors, there is no need to use a reduction gearbox when a radial plunger motor is put into use in that the motor can itself actuate crane winches or walking machinery wheels, etc.

    The following provides several calculation formulas helpful for hydraulic motors selection:

    calculation formulas

    After calculating the output power, torque and speed of various hydraulic motors, you can make an initial choice based on the estimated results and the general requirements of hydraulic system to ensure the torque generated by the selected motor should satisfy the working demands of the system. Subsequently, pick the right hydraulic pump that matches up with the motor’s flow and pressure.

    The following table shows the working conditions and application scope of different types of hydraulic motors and their specifications, which could guide your selection. You can either adopt low-speed motors or employ high-speed motors plus a decelerator for low-speed operation. As far as which solution is superior, it relies on your desired motor structure, area size, acceptable cost and driving torque.

    Working conditions and application scope of hydraulic motors

        Model     Characteristics & Working Conditions     Application Scope
     Gear Motors Simple-structured and easy for manufacturing. Large speed ripple, small and invariable load torque. Suitable for use under the conditions of undemanding speed stability, non-noise limit, high speed and low torque  Rotary hydraulic system for drilling machines, ventilation equipment, engineering machines, agricultural machinery and forestry machinery
     Vane Motors   Compact structure, small size, stable in movement and adjustable speed. Suited for conditions where small load torque is required.  Hydraulic system of grinders’ rotary table, machine tools’ operating mechanism, the automatic line and the servo mechanism
     Gerotor Motors Suitable for the working conditions where medium load speed is required and where few requirements are imposed on the machine size. Plastic machinery, coal mining machinery, excavators, etc.
    Axial Piston Motors  Compact structure, small radial dimensions and rotational inertia, adjustable speed. Suitable for occasions where high speed, large load, varying speed, slightly larger load torque, and low-speed stability are demanded.  Cranes, winches, forklifts, internal combustion locomotives, CNC machine tools, walking machinery
    Radial Piston Motors   Suitable for occasions where large load torque, medium speed, slightly larger radial dimensions are acquired.  Plastic machinery, walking machinery, etc.
    Internal Curved Plunger Motors  Suitable for occasions where maximum load torque, low speed and high stability are required. Excavators, tractors, cranes, etc.

    Specifications of common hydraulic motors

    Displacement Range ({in.}^3/rev) Pressure (MPa) Speed Range         ( r/min) Volumetric Efficiency (%) Total Efficiency(%) Mechanical Efficiency on Starting (%) Noise Price
    Min Max Rated Max            
    External gear motors 5.2 160  16-20 20-25 150—3000 85—94 85—94 85—94 Relatively Loud the Lowest
    Internal gear gerotor motors 80 1250 14 20    10—800 94 76 76 Low Low
    Double-acting vane motors 50      220 16 25 100—2000 90 75 80 Low  Low 
    Single swash plate axial piston motors 2.5      560 31.5 40 100—3000 95 90 20—25 Loud Relatively High
    Bent axis axial piston pump motors 2.5 3600 31.5 40 100—4000 95 90 90 Relatively Loud High 
    Steel ball plunger motors 250       600 16 25     10—300 95 90 85 Low Medium 
    Double swash plate piston motors         None          None 20.5 24      5—290 95 91 90 Low  High
    Single acting crank and connecting rod radial piston motors 188 6800 25 29.3      3—500 >95 90 >90 Low  Relatively High
    Single acting rodless radial piston motors 360 5500 17.5 28.5      3—750 95 90 90 Low Relatively High
    Multi-acting internal curved roller piston force transmission radial piston motors 215 1250 30 40       1—310 95 90 95 Low High
    Multi-acting internal curved steel ball piston force transmission radial piston motors 64 10000      16—20      20—25     3—1000 93 >85 95 Low Relatively High
    Multi-acting internal curved beam force transmission radial piston motors  1000 40000 25 31.5     1—125 95 90 95 Low High
    Multi-acting internal curved roller force transmission radial piston motors 8890 150774 30 35       1—70 95 90 95 Low High

    After determining the type of motor for use, select the desired motors with the right speed and torque. Calculate the pressure differential, flow and efficiency via characteristic curves related to varied specifications, and then conduct a comprehensive analysis, deciding on the particular specification for the technical and economic sake:

    1. If the historical cost matters most, you would better choose a motor with the right torque that can shrink the system flow and provide low pressures so as to reduce the specifications of hydraulic source, control valve and pipelines.
    2. If the operating cost is uppermost, a motor with high total efficiency should be an ideal choice.
    3. If the service life is a top priority, the motor with the smallest pressure drop is recommended.

    The final choice lies in, more often than not, a compromise of the above-mentioned solutions.

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