If you draw pneumatic schematics regularly, you probably have sources of standard hydraulic symbols. But if you only sometimes dabble in it or need other types of symbols to go with hydraulic or pneumatic symbols, you might want to check out Radica Software's Electrical, Pneumatic, Hydraulic and Electronic Symbols library, which offers hundreds of many types of symbols that are easily downloadable.
The library offers such oft-used components as hydraulic pumps, valves, cylinders, and motors, pneumatic valves, regulators, cylinders, and, of course, a wide variety of switches and other electrical components.
