Pneumatics and Control Valves Part 2

Air compressors are often called a hidden utility because not many people know about air compressors. The closest they get to an air compressor is the buzzing of air wrenches when they get their tires fitted. There are a myriad of pneumatic tools available on the market today. Cabinet and furniture shops use pneumatic nail guns and staplers, because nothing else compares to the speed and reliability of these tools. Blow off guns are the most common use for compressed air. From blowing off chips in a machine shop to a makeshift air brooms, these guns are extremely convenient tools. A blow off gun is simply a push button valve with a discharge valve to focus the escaping air. This type of gun is preferred when operators are restricted to specific machines, such as lathes, mills and punch presses.

Pneumatic energy is regulated and controlled by pneumatic valves. Functionally, valves are divided into four major groups viz, direction control, flow control, pressure control and non-return and special type valves. As per construction, valves are sub-grouped as seat valves and sliding or spool valves. However, spool valves are easier to manufacture. Valves are actuated in various methods, viz, manually, mechanically, electrically, pneumatically and by various combined mode of actuation. Specially designed valves like quick exhaust, time delay and shuttle and twin pressure valves are used to impart various functions to pneumatic circuits.

To control the to and fro motion of a pneumatic cylinder, the air energy needs to be regulated, controlled and reversed with a pre determined sequence in a pneumatic system. Similarly, one may have to control the quantity of pressure and flow rate to generate the desired level of force and speed of actuators. To achieve these functions valves are used. Valves are fluid power elements used for controlling and regulating the working medium, i.e, the compressed air in the case of a pneumatic system.

Board valves are used to start and stop pneumatic energy, control the direction of flow of compressed air, control the flow rate of compressed air and control the pressure rating of the compressed air. Direction control valves are mainly used to direct the flow of pressure fluid in the desired direction. They can be actuated to assume different positions by various actuating mediums. This results in corresponding connection or disruption of flow between various port openings. Direction control valves have two, three, four or five ports or openings.

In a direction control valve, the force is applied directly on the working piston or spool. The control method could be manual, mechanical, pneumatic, magnetic or a combination of any two. Magnets are commonly used for actuation of pneumatic valves. When the magnet is excited, the plunger gets attracted to it and it presses down on the valve spool. The pneumatic method acts on a spool or piston with a large area which in turn transfers the actuating force to the spool. Mechanical method involves the use of rollers, springs and other mechanical elements are used to actuate the valve. In the manual method the angular movement of a pedal or lever is transmitted to the spool.