From: zenadsl6186@zen.co.uk   
      
   tom perkins  wrote   
      
   >> From what I can tell, the gas is doing work in going from 6000 to 600   
   > psi.  The only significant losses are seen in the   
   > turbulence/shear/conversion to heat and noise occurring in the   
   > expansion valve.  Envision this:   
   >   
   > A layer of gas is at 600 PSI in the filled pump chamber on top of the   
   > propellant.  The propellant is at the required pressure, but is not   
   > moving to the engine.  More gas at initially 6000psi is admitted to   
   > the chamber, and this difference in pressure forces propellant to move   
   > into the engine.  The force exerted on the top of the propellant is   
   > moved by the newly admitted gas through the distance required to   
   > equilibrate the pressure of the newly admitted gas to 600psi, when   
   > motion and expansion stop.   
   >   
   > This motion is of course continuous, not intermittent, and the mean   
   > pressure of the gas during an expulsion phase is above 600psi, enough   
   > to overcome resistance losses and maintain a high flow rate.   
      
   Imagine this: the gas is first expanded from 6000 psi to 650 psi (without   
   doing any useful work) before it enters the cylinder. Would that make any   
   difference? No.   
      
   Or, if the gas was introduced all at once, so the initial pressure in the   
   cylinder was 6,000 psi and fell to 600 psi when the liquid was all expelled   
   - the liquid would be forced out at higher pressure (initially 6,000 psi,   
   falling to 600 psi), and the work done (= pv, pressure times volume) would   
   be greater.   
      
      
      
   --   
   Peter Fairbrother   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)