Pneumatics

Pneumatics and Hydraulics - Pneumatically operated - gas operated, Hydraulics - liquids

The RL-10 originally used Pneumatically operated valves:
1. With EMA, better control over rate of opening of valves
2. Always have supply pressure higher than chamber pressure
3. Oxidizer flow control valve is spring loaded, normally closed. Opens on pump pressure.
How fast spring loaded valve opens is determined by how fast the pump comes up. This limits 
control of O2 supply to igniter and combustion products upstream, controlling one valve 
(changing to EMA) and slowing its opening stopped backflow.

EMA proved more reliable and solved ignition problems by eliminating reverse pressure 
differential and backflow.


Pneumatics.
With Centaur - carry He to:
1. pessurize propellant tanks
2. expel propellants
3. operate valves on engines - valves regulate pressures
4. Purges - blow He to (~outside?)
During boost - blow He to keep atmospheric air out of the engine (AC-70, AC-71)
He is pressurized to 3000 psi
Tank pressures - inject enough He to maintain correct pressures
Fault tolerance - tanks hold 3 pressure transducers
take readings of transducers - all 3 agree - good
2 agree - use that
none agree (~??)

Main purpose of pneumatics is to keep fuel, LOX tanks pressurized.