Barış ERDEM (030060085) 9th Week

Positive Positioning

        A positive positioner (or positive-positioning relay) is designed to provide up to full main control air pressure to the actuator for any change in position. An increase in branch pressure from the controller moves the relay lever, opening the supply valve. This allows main air to flow to the relay chamber and the actuator cylinder, moving the piston. The piston movements is transmitted trough a linage and spring to the other end of the lever; and when the force due to movement balances out the control force, the supple valve closes, leaving the actuator in the new position. A decrease in control pressure will allow the exhaust valve to open until a new balance is obtained. Thus, full main air pressure is available, if needed, even though the control pressure mat have changed only a fraction of a psi.  The movement feedback linkage is sometimes mounted internally. Positioners may be connected for direct or reverse action. For large valves or dampers, main air to the actuator may be at higher pressure than pilot air.

(Roger W., Douglas C. H., Control Systems for heating, Ventilating, and Air Conditioning, 2006 p.38)

Tufram(Magnaplate)

Tufram is a lubricating coating developed by General Magnaplate Corp. The phase sepetaror that handles the Shuttle’s liquid waste is made of Turfam-coated aluminium. Designed by GE’s Space Systems Division, the unit works like this: A steam of air captures the liquid, directing it into the seperator. An impeller moves the air/water mix to centrifugal pump that seperates it. The water is pumped to a holding tank; the air is filtered and recirculated.

(Tough New Coating, Channels Shuttle’s Waste Water, Popular Science, Mar. 1977, p.190)

Over-damping

The effect of forces on an oscillating system is that the oscillations will evetually stop and the energy of the system will be dissipated mainly as thermal energy to the environment and the system itself. Oscillations taking place in the presence of resistance forces are called damped oscillations. The behaviour of the system depends on the degree of damping. We may distinguish three distinct cases: under-damping, critical damping and over-damping. In over-damping case degree of damping is so great that the system returns to equilibrium without oscillations (as in the case of critical damping) but much slower than in the case of critical damping.

(Tsokos K. A., Physics for the IB Diploma, p.208)