Will your hydraulics be available IF..

[dhardesthard]

Spannersatcx.

I believe that my statement is still accurate in that the hydraulic pressure will fall to below 3000 psi below normal idle speed. I did not say how far below but for argument sake 1/2 or 1% is below normal idle speed and you are certainly not going to get 3000 psi at 1%. Your hydraulic "light" that you refer to is a low pressure light and therefore will go out as the pressure increases to or reduces past a certain level. That light would be set to trigger at BELOW the NORMAL hydraulic pressure. Once again, if the hydraulic pressure(normal) is 3000 psi at idle rpm then it must at some time reduce to less than 3000 psi as the engine goes BELOW the normal idle speed, which is what I said.

[grounded27]

Next time I idle a motor I will pay more attention, I believe I was looking at a pw4000 on an MD-11 and it developed 3k psi by 10% N2.

[fizz57]

Aren't the EDP's positive displacement pumps? The question to ask is not what pressure it reaches when turning at low speed, but what will happen to that pressure if you put any demand on it.

[EW73]

Exactly, same with the airplanes I'm used to, at very low RPMs during starting, the hydraulic pressures are up fairly quickly, but it's pressure, not capacity until the pump RPM gets somewhere near normal.

Also, did I see someone earlier mention that he can run both aircon packs from one engine on a twin!
Not where I come from, a 737NG!

EW73

[FE Hoppy]

The E-jets idle the hydraulic pumps during engine starts to reduce starter loads so you don't see pressure until the start is well under way.( this is for in flight starts) Also for EW73, the E-jets can run 2 packs from one engine but the reduced flow restricts the aircraft to 31000ft. Above this it wouldn't meet the required lbs of air per passenger per minute. Some other aircraft are restricted to lower altitudes in the same condition.

[grounded27]

Aren't the EDP's positive displacement pumps? The question to ask is not what pressure it reaches when turning at low speed, but what will happen to that pressure if you put any demand on it.

You now have me recalling my DC-10 days, the electric pumps would often fault a full A/P systems RTS when used. 2 electric pumps feeding the two RMP's could not maintain the pressure upon demand. It was common practice to dry motor #2 engine, the output (volume) was much greater.