Pressure cylinder for machine tool clamp - has non-return valves which are held slightly off seats for low pressure clamping

摘要

A pressure cylinder is used to actuate the tool clamp of a machine tool and rotates with the tool. The double acting piston is controlled by a pair of spring loaded non-return valves which can be lifted off their seats by pistons. The springs must be sufficiently strong to close the valve against the effect of centrifugal force in the event of a supply pressure failure. But when only a light clamping pressure is needed it may be insufficient to open the valves. This difficulty is overcome by using a second piston which holds two balls very slightly off their seats.