Hydraulic Vs Pneumatic – Difference Between Pneumatic and Hydraulic Fluid System

Introduction To Hydraulic and Pneumatic :

What is Hydraulic and Pneumatic  system ? 

Fluid power is the technology that deals with the generation, control and transmission of forces and movement of mechanical element or system with the use of pressurized fluids in a confined system. Both liquids and gases are considered fluids. Fluid power system includes a hydraulic system (hydra meaning water in Greek) and a pneumatic system (pneuma meaning air in Greek). Oil hydraulic employs pressurized liquid petroleum oils and synthetic oils, and pneumatic employs compressed air that is released to the atmosphere after performing the work.

hydraulic vs pneumatic system
hydraulic vs pneumatic system

Perhaps it would be in order that we clarify our thinking on one point. By the term “fluid” we refer to air or oil, for it has been shown that water has certain drawbacks in the transmission of hydraulic power in machine operation and control. Commercially, pure water contains various chemicals (some deliberately included) and also foreign matter, and unless special precautions are taken when it is used, it is nearly impossible to maintain valves and working surfaces in satisfactory condition. In the cases where the hydraulic system is closed (i.e., the one with a self-contained unit that serves one machine or one small group of machines), oil is commonly used, thus providing, in addition to power transmission, benefits of lubrication not afforded by water as well as increased life and efficiency of packings and valves. It should be mentioned that in some special cases, soluble oil diluted with water is used for safety reasons. The application of fluid power is limited only by the ingenuity of the designer, production engineer or plant engineer. If the application pertains to lifting, pushing, pulling, clamping, tilting, forcing, pressing or any other straight line (and many rotary) motions, it is possible that fluid power will meet the requirement.

Comparison between Hydraulic and Pneumatic Systems

Usually hydraulic and pneumatic systems and equipment do not compete. They are so dissimilar that there are few problems in selecting any of them that cannot be readily resolved. Certainly, availability is one of the important factors of selection but this may be outweighed by other factors. In numerous instances, for example, air is preferred to meet certain unalterable conditions, that is, in“hot spots” where there is an open furnace or other potential ignition hazard or in operations where motion is required at extremely high speeds. It is often found more efficient to use a combined circuit in which oil is used in one part and air in another on the same machine or process. Table shows a brief comparison of hydraulic and pneumatic systems.

Hydraulic Vs Pneumatic -Comparison between Hydraulic and Pneumatic Systems

Hydraulic SystemPneumatic System
It employs a pressurized liquid
as a fluid
It employs a compressed gas, usually
air, as a fluid
An oil hydraulic system operates at
pressures up to 700 bar
A pneumatic system usually operates
at 5–10 bar
Generally designed as closed systemUsually designed as open system
The system slows down when leakage
Leakage does not affect the system
Valve operations are difficultValve operations are easy
Heavier in weightLighter in weight
Pumps are used to provide
pressurized liquids
Compressors are used to provide
compressed gases
The system is unsafe to fire hazardsThe system is free from fire hazards
Automatic lubrication is providedSpecial arrangements for lubrication
are needed
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