Adjustable volumetric hydraulic drives are widely used as drives for road, building, transport, lifting and agricultural machines, machine tools, rolling mills, press, etc. Such wide application is explained by a number of advantages of this type of drive in comparison with mechanical and electric drives.
Main advantages of hydraulic drives
- High specific power of hydraulic drive, i.e. transmitted power, per unit of total weight of elements. This parameter for hydraulic drives is 3 … 5 times higher than for electric drives, and this advantage increases with increasing transmission power.
- Relatively simply, it is possible to steplessly control the speed of the output link of the hydraulic drive in a wide range.
- High speed hydraulic drive. Start, reverse and stop operations are performed hydraulically much faster than other drives. This is due to the low moment of inertia of the hydraulic motor executive body (the moment of inertia of the rotating parts of the hydraulic motor is 5 … 10 times less than the corresponding moment of inertia of the electric motor).
- High power amplification factor of power amplifiers, the value of which reaches = 10 ^ 5.
- Comparative simplicity of technological operations at a given mode, as well as the possibility of simple and reliable protection of the driving motor and hydraulic drive components from overloads.
- Simplicity of transformation of rotational motion into reciprocating.
- Freedom of assembly of hydraulic drive units.
- Any hydraulic equipment can be connected to the hydraulic drive : jackhammers, circular saws, various buckets and grippers.
- Weak impact of vibration on the hands.
Along with the noted advantages of the hydraulic drive, when designing it or deciding whether it should be used, one should also remember the drawbacks inherent in this type of drive. These disadvantages are mainly due to the properties of the working medium (liquid).
The main disadvantages of the hydraulic drive
- The relatively low efficiency of the hydraulic drive and large energy losses when it is transmitted over long distances.
- Dependence of hydraulic drive characteristics on operating conditions (temperature, pressure). The viscosity of the working fluid depends on the temperature, and low pressure can cause cavitation in the hydraulic system or discharge of dissolved gases from the liquid.
- Sensitivity to contamination of the working fluid and the need for a sufficiently high maintenance culture. Contamination of the working fluid with abrasive particles results in rapid wear of precision steam elements in hydraulic assemblies and their failure.
- Decrease in efficiency and deterioration of characteristics of a hydraulic drive in process of development by it or its elements of an operational resource. First of all, the wear of precision pairs occurs, which leads to an increase in the gaps in them and an increase in fluid leaks, i.e. reduction in volumetric efficiency.
Thus, hydraulic actuators have, on the one hand, undeniable advantages over other types of drives, and on the other hand – some drawbacks. In this regard, the specialists associated with the design, manufacture and maintenance of hydraulic drives, set certain tasks.
The tasks of the designer in the design of the hydraulic drive are the optimization of its circuit, which ensures that the drive fulfills the functional requirements, and the reasonable choice of hydraulic drive elements.
The tasks of the technologist in the manufacture of hydraulic drive elements are to ensure the required high quality of production, as this has a huge impact on the performance of the hydraulic drive.
The tasks of the maintenance personnel during the operation of the hydraulic drive include the fulfillment of the technical conditions and the requirements for its operation, which consists, first of all, in the implementation of the hydraulic drive mounting rules, the regular replacement of the filter elements of the filters and the replacement of the working fluid and, if necessary, refilling it. The fulfillment of these requirements significantly prolongs the service life of both the individual components of the hydraulic drive and the entire hydraulic drive as a whole.