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The Fundamentals of
Pneumatics This is the fourth in a series of articles covering the basic principles of pneumatics. In the last article the internal working parts of filters, regulators and lubricators were discussed. We will continue our discussion of these components by explaining their schematic symbols and then go on to discuss flow controls. Schematic Symbols A diamond shape is used to indicate a device which conditions the air. By adding other symbols to the diamond we can tell if it is a lubricator, a filter or some other type of conditioning device. Figure 1A shows the symbol for a filter separator with a manual drain. The dotted line extending from the top of the diamond towards the bottom indicates a filter which removes dirt and contaminants from the air. The straight line across the bottom of the diamond indicates a separator where water and other contaminants can accumulate. The horizontal lines on the left and right side of the diamond indicate the input and output ports respectively. The line coming straight out the bottom of the diamond indicates a drain. This drain is manually operated and is used to drain the water from the bowl. Figure 1B is the symbol for a filter separator with an automatic drain. The V symbol added near the bottom of the diamond indicates the drain operates automatically. When the water reaches a certain level it will automatically drain the water out of the separator bowl. Figure 2 shows the symbol used to designate a regulator. The zigzag line coming out of the top of the symbol indicates the output pressure is adjustable. The horizontal arrow through the center of the square shows the direction in which the air flows through the regulator. The dotted line indicates a feed back. As air is used and the output pressure starts to drop, the regulator will allow more air to flow through it, which will maintain the output pressure at the correct level. A gauge is almost always used with a regulator so we can adjust the regulator for the output pressure required. |
The symbol for a lubricator is shown in Figure 3. Since the lubricator conditions the air it is also represented by a diamond. The straight line extending down from the top represents the tube from which oil can be dropped into the air stream. A drain is sometimes provided with a lubricator so that any water that might accumulate in the bottom of the bowl can be removed. Since water is heavier than oil it will accumulate on the bottom of the bowl, beneath the oil, and can be drained without draining the oil. A complete filter, regulator and lubricator (FRL) symbol can become quite involved, as shown in Figure 4A. Figure 4B shows the simplified version of an FRL symbol.
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