Pneumatic and hydraulic
- Category:Engineering and Construction
- Document type:Assignment
- Level:High School
PNEUMATIC AND HYDRAULIC SYSTEM REPORT
A successful design and development of a fluid power system is assisted by the use of a circuit bench. To effectively design and develop a pneumatic and hydraulic system, there must be a gear pump, double acting cylinder with 200mm stroke and 34mm cylinder bore. It is also necessary to have 2 units of directional control valve which could be either manual or solenoid. These will be available in order to start implementing these systems (Taylor & Francis, 2006). Notwithstanding, there must be 1 set of manual operated valve, 4-ways-3 positions and hydraulic pressure gauge, two sets of relief valves to control pressure and other check valves to control the flow of the fluids into the motor and hoses. Within the same bench, there must be other facility which is used to appraise the hydraulic stream, pressure and temperature.
This is a very essential report that focuses on the design pneumatic and hydraulic circuits systems. This report therefore mainly provides an overview of the structure of both hydraulic and pneumatic systems. It will also include a discussion on the benefits and drawback of the use of fluid power systems as opposed to electrical and mechanical power systems. Fluid power system is where force is produced, controlled and conveyed through the use of pressurized fluids. This system uses both fluids and gases to generate force the triggers motion of mechanical parts of the system (Eaton et al, 2001). The generation of power through fluids involves the use of both hydraulic and pneumatic systems and each employ oil or air to induce mechanical force. Hydraulic system utilizes pressurized petroleum oil while pneumatics use compressed air. The purpose of this report is to discuss the development and accomplishment of fluid power systems in a manufacturing company.
2.0 Report Analysis
2.1 Pneumatic or Hydraulic multi-actuator sequential operation circuit
There are various methods through which multi-actuator can be designed although there is no universal design method that can be used for all circuits (Taylor & Francis, 2006). There are also some methods which are necessary for compound circuits but they seem very costly. Five methods are available but only one can be chosen for the design of a multi-actuator design.
In the application of pneumatic system, there is need to use more than one cylinder, the movements of these cylinders are controlled according to the expected sequence. It is vital to use sensors to identify the location and position of the cylinder in order to have good control of actuation (Butterworth, 1998). This is achieved through the use of limit switches and there is also a need to introduce activation switches to each cylinder to ensure that there is a proper control of the movement of each cylinder. More importantly, all the limit switches must be arranged in good locations with the assistance of motion diagram.
2.2 Pneumatic or Hydraulic rotary actuation system that includes speed control in both directions
A rotary actuator is a useful output device. It is responsible for producing oscillating movements within a controlled arc.
It is necessary in a situation where rotary output that has high torque at a low velocity is used. The rotary can only produce torque when there is an exposure of fluid pressure against vane surfaces. It is important to construct actuator for both the two systems depending on the size of the machine (Eaton et al, 2001). The vane type are available in two different forms including single vane that has a maximum angular rotation of 280 degrees or a double vane that has a maximum of not more than 100 degrees. It is important to use double vane because it have the ability to produce twice the torque. It is only limited to half of angular motion.
It is possible to use any spool type of directional valve1 to direct the cylinder. It is a must that it must have a center neural location although 2 position valves are not needed in this case (Butterworth, 1998). Its velocity should also be minimized when close to the end of the arc to limit chances of damaging vane. It is possible to decelerate it and this can be done in 2-way. The switches attached at the end of the stroke should be limited to actuate all valves 2 and 3. This will influence the main flow to follow a different direction but passing through pre-set needle valve 8 and 9. This will reduce the speed of the flow of the fluids. It is also possible to take advantage of speed valve 4 and 5 and they can also be used to reduce the flow rate in either direction. The circuit must be designed in this way to remove speed control. This will ensure that there is no wastage of power and heating of oil. I highly recommend the use of cushion relief valve in areas where the actuator is expected to pause by flowing into 4-way valve (Taylor & Francis, 2006). The relief valve should have a setting of 500PSI or above that of the pump. I think that that valve should be nonadjustable to ensure that they are not tampered with or raised too high.
2.3 Electro-pneumatic or electro-hydraulic system for a double acting cylinder
Electro-pneumatic or electro-hydraulic system for a double acting cylinder is also made up of in-built solenoid located at the left. It also has in built springs at the end of valves located at the right hand side (Butterworth, 1998). The above diagram shows its electrical circuit meant for actuating a double acting cylinder through the use of 4/2 DCV single solenoid. When the operator pressed the pushbutton S1, there is an activation of coil R1whih turn on the NO K1 switch. Once the K1 is active, it will also activate Y1 which allows solenoid Y1 to alter the location of the valve. This will induce the oil to start flowing to the left cylinder and through this the cylinder rode will extend allowing the fluid to flow in all the valves.
2.4 Pneumatic or Hydraulic ‘Fail safe’ detection function for linear actuation.
This is an actuator that triggers motion along a straight-line (Butterworth, 1998). It uses energy from an outside source and there are different methods through which straight-line motion can be achieved. It can be achieved through hydraulic or pneumatic actuators. It is therefore necessary to design it as shown above. In order to perform linear actuation, it is important to have valve stem stroke length, actuating time, and a seating thrust.
Currently most companies prefer using fluid power system as opposed to mechanical or electrical power system. This is because fluid power system generates more power and also run the machine at a very low cost. The hydraulic and pneumatic systems usually require less initial cost and also simple design. Since the air system or fluid system require less pressure to transmit power to different parts of the machine, it can easily be made locally available materials. It is easier to develop and implement pneumatic system than hydraulic system because air circuit is cheaper than hydraulic circuit although pneumatic system require higher operating cost than hydraulic circuit. It is therefore preferable for a manufacturing company to use either of these power systems when running their machines or plants (Butterworth, 1998). It is estimated that the cost of operating air circuit is more than five times that of hydraulic circuit but cheaper than mechanical and electrical power systems. In order to compress atmospheric pressure to a level that can be used in pneumatic system require higher horsepower and this increases the cost of using hydraulic and pneumatic system. This is because it requires one horsepower to pressurize 4cfm of atmospheric air to 100 psi but A1-hp air motor can consume approximately 60cfm to operate efficiently. Therefore 1-hp air motor can only use 60/4 compressor horsepower to run as the company expects. The only problem air motor has is that it does not work continuously and therefore need recycling as soon as possible to make machine run.
It is also important to note that air driven machines are usually less noisy as compared to when hydraulic systems. This is due to the fact that air driven machines usually have its air compressors installed remotely in a separate enclosure which contains the noise. Air driven actuator can only hold a lighter load as compared to hydraulic actuator because compressibility of air but for it to work efficiently it can only employ air or oil for power generation. Air and oil can be used simultaneously although it increases the cost of operation. Based on my analysis, air operated systems are usually cleaner and therefore cannot pollute the environment and therefore it is costly as compared to hydraulic operated machines.
A hydraulic system is equally very important as compared to pneumatic system. It uses fluids such as oil to transmit power from fixed reservoir to other parts of the system. It uses non compressible liquids and therefore it has actuators which it can control accurately at a high speed and force in a right position (Taylor & Francis, 2006). Hydraulic circuit always applies mineral oils as the main media for its operations although there are other liquids such as water and ethylene glycol which it can also use when operating. The system usually makes use of dedicated power unit with different pipes connecting it to and from the presses. When the system is closed for a longer time, these presses do not have flow although one large pump can be used to operate all of them in the same plant. The hydraulic system is has the same operation as pneumatic system because both of them has one source of power located at the same point. There are other manufacturers that install central power unit when they have a plant that is connected to different machines that apply hydraulic systems. This kind of a design minimizes machine noises and also provides a backup pump which supports the machine when other pumps fail. Another important advantage of using the above configuration is that it requires the use of less horsepower and flow and this increases uptime of all the machines connected to central power unit.
Taylor & Francis, (2006) Hydraulic Power System Analysis. Good text on hydraulic system analysis.
Butterworth H (1998) Hydraulics and Pneumatics: A technician’s and engineer’s guide. Good introductory overview of fluid power systems.
Eaton-Vickers, Industrial Hydraulics Manual. Eaton Corportation, (2001).A standard text for training fluid power technicians. Contains good, practical information. Used in the fluid power lab course at the University of Minnesota.