what is hydraulics

When engineers and technicians ask "what is hydraulics," they are inquiring about one of the most powerful and versatile transmission methods in modern mechanical engineering. Hydraulic transmission possesses numerous advantages compared to mechanical transmission systems, which explains its widespread adoption across various industries and applications.

Hydraulic transmission represents a sophisticated method of power transfer that utilizes liquid as the working medium to transmit energy efficiently. This transmission form operates through energy conversion devices, such as hydraulic pumps, which transform the mechanical energy from prime movers (like electric motors) into liquid pressure energy. Subsequently, through closed pipelines and control elements, another energy conversion device (such as hydraulic cylinders or hydraulic motors) converts the liquid pressure energy back into mechanical energy to drive loads and achieve the required linear or rotational motion of actuating mechanisms.

Understanding what is hydraulics becomes essential for modern engineers, as this technology forms the backbone of countless industrial applications. The fundamental principle behind hydraulic systems lies in Pascal's law of hydrostatic pressure transmission, which enables the multiplication of force through fluid mechanics principles.

This comprehensive examination covers the development history of hydraulic transmission, its operational principles, system composition, advantages and disadvantages, and the extensive applications of hydraulic technology across various sectors of modern industry.

Relative to mechanical transmission systems, hydraulic transmission represents a relatively modern technological advancement. The origins of hydraulic transmission can be traced back to 1654 when Pascal proposed the fundamental principle of hydrostatic pressure transmission. This groundbreaking concept laid the theoretical foundation for all future hydraulic developments.

The practical implementation of hydraulic principles began in 1795 with the emergence of the first hydraulic press in Britain. However, the technology remained limited until 1905, when engineers made the crucial decision to replace water with oil as the working medium. This substitution resulted in dramatic performance improvements and marked a turning point in hydraulic technology development.

The widespread adoption and application of hydraulic transmission systems benefited significantly from the petroleum industry that emerged and flourished during the 19th century. The availability of refined oils provided the necessary working fluids that made hydraulic systems practical and reliable for industrial applications.

The earliest successful application of hydraulic transmission devices occurred in naval vessels, specifically in gun turret positioning systems. These applications demonstrated the superior control capabilities and power transmission efficiency that hydraulic systems could provide in demanding military environments.

During World War II, military industrial requirements for rapid response, high precision, and high-power hydraulic transmission devices further accelerated the development of hydraulic technology. The demands of warfare pushed engineers to develop more sophisticated and reliable hydraulic systems, leading to significant technological breakthroughs.

Following the war, hydraulic technology rapidly transitioned to civilian applications and gradually gained widespread adoption across various sectors of the national economy. The 1960s marked another significant period of advancement, as developments in atomic energy, space technology, and computer technology drove corresponding innovations in hydraulic systems, leading to their penetration into virtually every industrial field.

Currently, hydraulic technology continues evolving toward higher speeds, higher pressures, greater power output, improved efficiency, reduced noise levels, extended service life, increased integration, compound functionality, digitization, miniaturization, and weight reduction. Additionally, contemporary research focuses on new hydraulic components and systems incorporating computer-assisted testing (CAT), computer direct control (CDC), mechatronic integration, computer simulation and optimization design techniques, environmentally friendly water-based transmission technology based on green manufacturing principles, and advanced contamination control methods.

China's hydraulic technology development began in 1952, with hydraulic components initially applied to machine tools and forging equipment before expanding to construction machinery. In 1964, China imported hydraulic component production technology from foreign countries while simultaneously developing domestic hydraulic products through independent design efforts.

Through years of dedicated development, particularly following the introduction of advanced technology and equipment from the United States, Japan, and Germany in the early 1980s, China's hydraulic technology reached new heights. Currently, China has established comprehensive standardized, serialized, and universalized hydraulic component product lines covering all major categories.

Timeline of Hydraulic Technology Development

To understand what is hydraulics in practical terms, we can analyze a simple hydraulic transmission system designed for a machine tool that achieves reciprocating motion of a worktable. This system demonstrates the fundamental operating principles that govern all hydraulic applications.

In this representative system, the hydraulic cylinder remains fixed to the machine bed, while the piston and piston rod combination drives the worktable in linear reciprocating motion. An electric motor drives the hydraulic pump rotation, which draws oil from the tank through a mesh filter. The oil flows through a throttle valve to reach a directional control valve.

When the manual handle occupies the neutral position, the pump port (P) remains disconnected from ports A, B, and the tank return (T). Under these conditions, the hydraulic cylinder receives no oil supply, resulting in stationary worktable operation.

Moving the handle to position the system for rightward motion creates a flow path from P to A, directing oil to the left chamber of the hydraulic cylinder. Simultaneously, oil from the right chamber returns through port B to the tank via port T, causing rightward worktable movement.

Conversely, positioning the handle for leftward motion establishes flow from P to B, supplying oil to the right chamber of the hydraulic cylinder. The left chamber returns oil through port A to the tank via port T, resulting in leftward worktable movement.

This analysis demonstrates that the directional control valve enables hydraulic oil path changes, allowing continuous hydraulic cylinder direction reversals to achieve worktable reciprocating motion. The worktable speed can be regulated through the throttle valve, which controls oil flow rate by adjusting the throttle opening size.

During worktable operation, the system must overcome resistance forces, cutting forces, and surface friction between relatively moving components. The hydraulic pump output pressure overcomes these resistive forces, with pressure adjustability based on varying operating conditions. Additionally, hydraulic pump output often exceeds hydraulic cylinder requirements, with excess oil returning to the tank through the relief valve.

From the preceding example, hydraulic transmission systems comprise five essential components:

Each component plays a crucial role in answering what is hydraulics from a practical system perspective, demonstrating how these elements work together to create functional hydraulic transmission systems.

The hydraulic transmission system diagram represents a semi-structural schematic that provides strong visual clarity and easy comprehension. However, such diagrams become complex and difficult to draw, particularly when systems contain numerous components. To simplify schematic drawing processes, system components can be represented using standardized symbols that indicate component functions without representing structural details or parameters.

The national standard GB/T 786.1-2009 establishes hydraulic component functional symbol standards for consistent representation across the industry. Understanding these symbols becomes essential when learning what is hydraulics from a practical design perspective.

To facilitate comprehension of hydraulic system diagrams using functional symbols, the following introduces graphical symbols for hydraulic components:

Hydraulic system diagrams specify that component graphical symbols should represent static states or zero positions. Consequently, complex structural diagrams can be simplified into functional symbol representations that maintain technical accuracy while improving drawing efficiency and system comprehension.

Overall, hydraulic transmission advantages outweigh disadvantages, with ongoing production technology developments gradually addressing limitations. Consequently, hydraulic transmission finds widespread application across national economic sectors with broad development prospects in modern production environments.

Understanding what is hydraulics includes recognizing its extensive applications across various industries. The following table illustrates hydraulic transmission applications across different sectors:

Different sectors adopt hydraulic transmission for varying reasons: construction machinery and press machinery utilize hydraulic transmission for structural simplicity and high output forces; aviation industries choose hydraulic transmission for lightweight and compact characteristics; machine tool applications primarily benefit from stepless speed variation, automation capabilities, and frequent reversing motion implementation.

Machine Tool Applications in Detail