The pneumatic elements are most commonly used to resemble and take the function of hydraulic cylinders in appropriate models, actuating a digging arm or crane, for example. They can, however, also be used to build a pneumatic engine, which converts air pressure into rotary motion using the same principles as a steam engine. However, the cylinders are not optimised for this purpose, and such engines tend to be slow and lack power unless the cylinder inlets are enlarged. Because a slight delay is involved between increased pressure and cylinder movement, various feedback loops can be used whereby one pneumatic component can activate another in a series of mechanical events.