Hydraulics & Pneumatics

HYDRAULICS IN MISSILES

Nowadays, the electro-hydraulic actuator plays an important role in some modern tactical missiles. High power, great robustness and high tracking precision are the most significant demands for the missile actuator. Therefore an advanced method of active disturbance rejection control (ADRC) is presented aiming at the dynamics of the system are highly nonlinear and have large extent of model uncertainties, such as tremendous changes in load. Firstly, a novel ADRC controller is designed for estimating and compensating disturbance based on the mathematical model of missile electro-hydraulic actuator. Then, the influence of rudder load on the system performance is analyzed in this paper. Simulation results show that the ADRC control approach can decrease the tracking error and enhance the robustness of missile electro-hydraulic actuator system when the rudder load changed tremendously. But the phenomenon of Anti-Control has disadvantageous effect on the transition period of actuator loop and evenly causes the system divergence.

HYDRAULIC SUSPENSION IN BOGIES
The application of oil-hydraulic actuators for active suspension of railway vehicles has been examined experimentally by using a 3-DOF half-vehicle model. The LQG control law was adopted, in which state variables were estimated from measurable ones on the actual railway vehicle. The results show the possibility that the controllable frequency range extends with the oil-hydraulic actuator. The addition of bogie acceleration measurement to body related measurement provides a significant advantage for the performance. When actual body weight becomes lighter than that of the controller design value, the control performance and the stability deteriorate. Therefore, it is recommended to use the empty car body weight for design of the active suspension controller. The control effect can reach to the maximum vibration isolation level by shortening the sampling period to 2 ms

PNEUMATIC GREASE GUN

A grease gun is a common workshop and garage tool used for lubrication. The purpose of the grease gun is to apply lubricant through an aperture to a specific point, usually on agrease fitting. The channels behind the grease nipple lead to where the lubrication is needed. The aperture may be of a type that fits closely with a receiving aperture on any number of mechanical devices. The close fitting of the apertures ensures that lubricant is applied only where needed. There are three types of grease gun:

A grease gun (pneumatic)
1. Hand-powered, where the grease is forced from the aperture by back-pressure built up by hand cranking the trigger mechanism of the gun, which applies pressure to a spring mechanism behind the lubricant, thus forcing grease through the aperture.
2. Hand-powered, where there is no trigger mechanism, and the grease is forced through the aperture by the back-pressure built up by pushing on the butt of the grease gun, which slides a piston through the body of the tool, pumping grease out of the aperture.
3. Air-powered (pneumatic), where compressed air is directed to the gun by hoses, the air pressure serving to force the grease through the aperture. Russell Gray, inventor of the air-powered grease gun, founded Graco based on this invention
The grease gun is charged or loaded with any of the various types of lubricants, but usually a thicker heavier type of grease is used.
It was a close resemblance to contemporary hand-powered grease guns that gave the nickname to the World War II-era M3 submachine gun.

PNEUMATICS IN AIRCRAFT

Bleed air in gas turbine engines is compressed air taken from within the engine, after the compressor stage(s) and before the fuel is injected in the burners. While in theory bleed air could be drawn in any gas turbine engine, its usage is generally restricted to jet engines used in aircraft. Bleed air is valuable in an aircraft for two properties: high temperature and high pressure (typical values are 200-250°C and 275 kPa (40 PSI), for regulated bleed air exiting the engine pylon for use throughout the aircraft).[1] This compressed air can be used within the aircraft in many different ways, from de-icing, to pressurizing the cabin, to pneumatic actuators. However, bleed air is quite hot and when being used in the cabin or other low temperature areas, it must first be cooled or even refrigerated by the aircraft's environmental control system (ECS). Newer aircraft rely more on electricity, reducing the need for compressed air. Since most gas turbine engines use multiple compressor stages, some newer engines have the bleed air inlet between compressor stages to reduce the temperature of the compressed air.