Can Any Of You Put An Answer To This Question?

[steven b]

HI GUYS

CAN ANY OF YOU HELP ME OUT WITH THESE
ONE OF THE FUNCTIONS OF THE HYDRAULIC ACCUMULATOR IS
1ABSORB POSSIBLE POWER SURGES..2PRESSURIZE THE HYDRAULIC FLUID..3PREVENT FLUID FOAMING AND CAVITATION..4COMPENSATE FOR FLUID LOSSES DURING LEAKAGE

IF THE A/C ALTIMITER WAS SET TO QFE AND CABIN ALT TO ZERO THEN AT THIS AIRFIELD..1CABIN WILL BE PRESSURISED AT TOUCHDOWN..2CABIN WILL HAVE AN ALT OF 8000...3CABIN WILL HAVE NEGATIVE PRESSUE AT TOUCH DOWN..4NO DIFFERENTIAL PRESSURE AT TOUCH DOWN

PRIOR TO MAIN STARTING..1ONLY AIRCON AVAILABLE FROM APU..
2PRESSURISATION AVAILABLE FROM APU..3ONLY ELECTRICAL POWER FROM APU
THANKS TO ALL WHO HELP

[LME (GOD)]

OK, You should be able to find all ofthis in your books as they are fairly basic...
1. One of the functions of a hydraulic accumulator is..to asborb power surges from the pump, alo in some systems to provide emergency actuation in the event of pressure loss eg. brakes

2. The answer would seem to be "c" but most aircraft pressure controllers will be trying to acheive a negative diff px of .125 psi. (boeing yes, not sure about the airbus)

3. When "start" is selected and the APU is running and fully online. The packs will either turn off automatically or have to be seleced off by the crew as part of the start checklist. Electrical supply will remain unaffected until Engine Gene's come up to speed

[GlueBall]

Our APU is powerful enough to start a motor with one pack running.

[Lu Zuckerman]

Almost totally correct

1. One of the functions of a hydraulic accumulator is..to asborb power surges from the pump, also in some systems to provide emergency actuation in the event of pressure loss eg. brakes

Both answers are correct but the primary purpose of the accumulator is to “try to maintain system pressure” when the pilot places a load on the system during flight control movement. An accumulator is used primarily in a system that does not have a compensated pump. This type of pump is normally referred to as a variable delivery constant pressure pump. This is a misnomer because even a variable delivery constant pressure pump can’t maintain full pressure in the system when the servos require a high flow rate. As the demand is placed on the system the pump will only maintain the pressure at a level to accomplish the work of the servos.

In other words if your system pressure is rated at 3000 PSIG and it only takes 2000 PSIG to overcome the feedback control loads then the pump will only put out 2000 PSIG that is until the servo movement stops and then the pressure will rise to 3000 PSIG. The accumulator on the other hand tries to keep the pressure at a level sufficient to overcome the loads on the system until the pump catches up and repressurizes the accumulator. Some helicopter servos have a built-in accumulator to allow some control movement in the event of pressure loss.