However, because of the compressibility of air, it is impossible to obtain precise, controlled actuator velocities with pneumatic systems. Also, precise positioning control is not obtainable. In applications where actuator travel is to be smooth and steady against a variable load, the air exhaust form the actuator is normally metered. Whereas pneumatic pressures are quite low due to explosion dangers involved if components such as air tanks should rupture (less than 250 psi), hydraulic pressures con be as high as 12,000 psi. Thus, hydraulics can be high-power systems, whereas pneumatics are confined to low- power applications.