Stroke speed is regulated with a flow control valve. Installed in the air line between the directional control valve and the cylinder, the flow control valve governs speed by controlling the flow of exhaust air from the cylinder. For double-acting cylinders, two flow control valves are required. A muffler or sandwich can also be applied to the exhaust air to control speed.
Either way, the key is regulating the exhaust air, says Richard Porqueddu, product management for handling systems at Festo Corp. (Hauppauge, NY). This arrangement maximizes control over the cylinder, because the full line pressure is used for actuation. The upstream volume of the retracted cylinder is small and reacts instantly to full pressure. The larger, downstream volume bleeds off relatively slowly, allowing the cylinder to advance on a cushion of air.