Comparison of Hydraulic and Pneumatic Drive Systems - Essay Example

Historical Background of Hydraulic and pneumatic Drive Systems The technology used in modern systems used in manufacturing dates back to the old days of civilization where water turbines were used to generate power. Hydraulic systems for instance were used in old aircrafts in braking. Modern aircrafts have more sophisticated and improved systems for power transmission. In a bid to make work easier, modern technological equipment such as but not limited to tractors and forklifts have been designed and they use power transmission mechanisms which are more effective. Power transmission can be done using either air or liquids. It involves pressurizing the liquid or gas which transmits power from one point to another in accordance Pascal’s principle. Hydraulic (hydrostatic) systems use compressed incompressible liquids to transmit power from one point to another. On the other hand, pneumatic (air-powered) system uses compressed air to transmit power from one point to another. As earlier mentioned, the development of these drive systems dates back to the ancient days of civilization. Hydraulic drive systems were used in the ancient times and artifacts indicate that water mills which were invented back in 100 BCE used this system (Tan & Putra, 2010). Major developments such as the one done by Pascal (Pascal’s Principle) and the Bernoulli’s hydrodynamic law of 1750 have revolutionized these drive systems (Tan & Putra, 2010). Additionally, the 20th century industrial revolution and world war II were also major catalysts of development of these drive systems. It saw the improvement of drive systems to use incompressible fluids such as oil as opposed to compressible (water) which was used earlier before. They were adopted because they were more effective than those used before. Hydraulic drive systems are still in use up to date. As a matter of fact, they have many applications because of its high power to weight ratio hence making them suitable for heavy machines (Tan & Putra, 2010). In addition to this, hydraulic drive systems are used in many cases because of its preciseness during start of operation, accuracy and its flexibility (Tan & Putra, 2010). A hydraulic drive system comprises of the power source (electric motor), hydraulic pump, pipes and valves and hydraulic actuator as shown in the schematic diagram below. In a hydraulic system, the hydraulic pump is powered by the power source which is similar to an electric motor only that it uses a fluid as a source of power rather than electric current. The running of the hydraulic pump results to generation of fluid flow within the pipes to the hydraulic actuator which drives the load (Tan & Putra, 2010). The interest of expanding the use of fluid to transmit power led to the development of pneumatic drive system. The need to develop aircrafts with more power during the World War II was a major accelerating factor of development of pneumatic system. Pneumatic system provided a solution to this need for more powerful aircrafts and it led to the replacement of cable-operated system with button operated systems (Tan & Putra, 2010). Development of this drive system was a big boost to the aviation industry. For instance, the door operation in aircrafts uses this system. Hydraulic system and pneumatic drive system are similar in terms of their components. It has a power source, compressor, pipes and valves and pneumatic actuator. The schematic sketch of pneumatic circuit is as shown below. The working of a pneumatic drive system is similar to that of hydraulic system. The only difference is the hydraulic pump which is replaced by a pneumatic compressor in the pneumatic system. In both systems, sensors and transducers, and controllers are included to give signal readings to the controller which manipulates the controllable elements (Tan & Putra, 2010). Comparison between Hydraulic and Pneumatic Systems Each system has its own characteristics which makes it suitable for a specific application. A common characteristic which differentiates between the two is the manner in which each of them react. While hydraulic drive system reacts instantly, pneumatic reaction has a delayed reaction (Tan & Putra, 2010). This characteristics originates from the fact that gases are compressible while most liquids are incompressible (Goodheart-Wilcox, 2010). Instant reaction in hydraulic system which uses liquid oil is as a result of incompressibility of oil. Another major characteristics that differentiates between the two is the complexity of the design. Hydraulic drive systems have more complex designs while pneumatic type uses a simple design (Tan & Putra, 2010). The main reason why hydraulic systems require a complex design is because of the high pressure involved. Pneumatic system operate on very low pressure thus does not require a complex system. This translates to the cost of each system which brings out the difference between the two. For hydraulic systems which have complex designs, it means that they are costly compared to pneumatic designs (Tan & Putra, 2010). Additionally, hydraulic drive systems are very effective in that unwanted movements while holding the load are completely eliminated while in pneumatic drive systems, unwanted movements are always there. Advantages of Hydraulic Drive Systems Hydraulic drives have remained as the most preferred drive systems because of the many advantages it has. One major advantage when compared to pneumatic is high power output to weight ratio (Tan & Putra, 2010). Small systems deliver high power output. They can therefore be used in handling heavy loads. It is the main reason why these systems are used areas of explosives since they have high output power and cannot get damaged easily when stopped suddenly (Patrick & Fardo, 2009). Additionally, the system uses a liquid preferably oil in generating and transmitting power. The same oil acts as a lubricant and cools the system. Therefore, the system does not suffer from the problem of overheating or viscosity. The fact that most liquids are incompressible results to high accuracy of movement which makes hydraulic drive systems suitable for cases where higher accuracy is required in the movement (Goodheart-Wilcox, 2010). Additionally, as it has been mentioned earlier hydraulic systems react instantly. This characteristic makes this system suitable for movements that require instant stoppages and reverse movement (Goodheart-Wilcox, 2010). Moreover, it offers an opportunity for both rotational and linear motions (Patrick & Fardo, 2009). Disadvantages of Hydraulic Drive Systems Although they are preferred, hydraulic drive systems have some disadvantages. One major disadvantage stems out from the fact that liquids are used which poses danger of leakage, contamination and explosion (Tan & Putra, 2010). This characteristics makes the system not suitable for cases where the system is required to be clean such as in food manufacturing processes (Patrick & Fardo, 2009). The complex nature of the system required for hydraulics makes it very costly to install and maintain when compared to the pneumatic system which uses a simple system (Patrick & Fardo, 2009). This in itself is a disadvantage of hydraulic system. Advantages of Pneumatic Drive Systems Pneumatic systems have some advantages compared to hydraulic systems. One major advantage of pneumatic drive system over hydraulic system is the cost. Most industrial set ups have compressed air systems fabricated in the assembly (Patrick & Fardo, 2009). Air is readily available and this reduces the cost of installing a pneumatic system. Moreover, these systems are less complex hence further bringing down the cost of installation of the entire system. It is for this reason that pneumatic robots are cheaper than hydraulic counterparts in terms of installation (Patrick & Fardo, 2009). The nature of design of pneumatic drive systems makes the cost of operation and maintenance low compared to hydraulic counterparts. The fact that air is used makes pneumatic systems suitable for use environments susceptible to explosion (Patrick & Fardo, 2009). Furthermore, they are suitable for high speed operations. Pneumatic actuators can attain speeds of 20,000 cycles per minute (Goodheart-Wilcox, 2010). In fact they are preferable in small to medium loads that require high speed operation (Patrick & Fardo, 2009). Disadvantages of Pneumatic Drive Systems Pneumatic drives have a number of disadvantages. One of the demerits of these systems originates from the fact that air is compressible. This makes the system not suitable for high precision placement. Another major disadvantage of pneumatic systems is noise. Although this characteristic is possessed by hydraulic systems, pneumatic systems are noisier than the hydraulic counterparts. Noise originates from the vibration of cylinders and motors (Patrick & Fardo, 2009). The efficiency of pneumatic systems largely depend on purity and moisture content of air in the system. As a matter of fact it is quite difficult to purify the air used and reduce the moisture content (Patrick & Fardo, 2009). This brings down the efficiency of the system and it is the reason why their efficiencies are lower than hydraulic systems. References Goodheart-Wilcox. (2010). Introduction to Fluid Power. Goodheart-Wilcox Co., Inc. Patrick, D. R. & Fardo, S. W. (2009). Industrial Process Control Systems. New Delhi: The Fairmont Press Inc. Tan, K. K. & Putra, A. S. (2010). Drives and Control for Industrial Automation. New York: Springer Science and Business Media. Read More