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Figure 7 shows the symbol for a double-acting, double-rod air cylinder. It is double-acting because air can enter and be discharged from either end of the cylinder; and double-rod because the rod will extend out the left end of the cylinder when air enters port B, or out the right end of the cylinder when air enters port A. Figure 8 shows a typical double-acting, double-rod air cylinder. There are several factors which determine the amount of force an air cylinder can produce. For example, a large diameter cylinder will produce a greater force than a smaller diameter cylinder. Also, increasing the air pressure to the cylinder will increase the amount of force. The speed of an air cylinder is determined by the flow of air in cubic feet per minute (CFM) to the air cylinder. If we restrict the flow to a cylinder, it will move slowly. On the other hand, if we allow the air to flow to a cylinder unrestricted it will move with great speed, PRESSURE causes FORCE. FLOW causes SPEED. When regulating the speed of an air cylinder, the exhaust air coming out of the cylinder should be controlled rather than the air entering the cylinder. Controlling the exhaust air tends to give smoother and more consistent speed control of the air cylinder. In some applications of a single-acting air cylinder, controlling the exhaust air will regulate the speed of the cylinder in only one direction. In these cases the input air must be controlled to regulate the speed of the cylinder in the other direction. In the next article we will analyze some pneumatic circuits which utilize the filters, regulators, lubricators, directional control valves, actuators and air cylinders we have discussed in this series of articles. NE |
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