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FSXA Auxiliary hydraulic system (SOLVED)

I downloaded a Manual.
Normal Lear hydraulic pressure at idle and above is 1500 to 1575.
On the ground before engine start, if the hyd pressure is less than 1000, the auxiliary pump is turned on until the Parking Brake light is illuminated. Then it is switched off
Therefore the auxiliary pump output is at least 1000 psi
Green range for Hyd pressure is 1000 to 1750 and 1750 is redline.
The accumulator minimum pressure is 750. This is usually ensured by charging it with air. The purpose of the accumulator is to smooth out pressure drops from sudden demands, stops the pipes hammering.
In the air the auxiliary pump is only used in emergencies, for example to lower flap after engine pumps fail or engines fail.
Roy
 
But there is no variable for just total hydraulic pressure. I only see that you have pressure based off of each engine or each pump. This is why i designed it as additive. But after thinking about what you said it makes no sense to have it additive.
ENG HYDRAULIC PRESSURE:index

The way i figured this is this is for each pump
HYDRAULIC PRESSURE:1 HYDRAULIC PRESSURE:2 + = total
And this is for each engine
ENG HYDRAULIC PRESSURE:1 ENG HYDRAULIC PRESSURE:2 + = total
So if there is no total hydraulic pressure it made me think it's additive.

I do agree that the auxiliary pump should not be half the pressure. I am going to update so the auxiliary is 1500 psi for normal operation and write a new code for the gauge.
 
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To not go additive the hydraulic gauge had to be written like this so in a sense i am only reading the pressure from 1 engine at a time. This makes no sense. How would you write the code for the total hydraulic pressure with 2 engines or 2 pumps?
Code: 
    (A:ENG N1 RPM:1, Percent) 22 < (A:ENG N1 RPM:2, Percent) 22 < and if{ (A:HYDRAULIC PRESSURE:1, PSI) 10 / }
    (A:ENG N1 RPM:1, Percent) 22 > (A:ENG N1 RPM:2, Percent) 22 > and if{ (A:HYDRAULIC PRESSURE:1, PSI) 10 / }

    (A:ENG N1 RPM:1, Percent) 22 > (A:ENG N1 RPM:2, Percent) 22 < and if{ (A:HYDRAULIC PRESSURE:1, PSI) 10 / }
    (A:ENG N1 RPM:1, Percent) 22 < (A:ENG N1 RPM:2, Percent) 22 > and if{ (A:HYDRAULIC PRESSURE:2, PSI) 10 / }

My original used this: Additive
Code: 
   (A:HYDRAULIC PRESSURE:1, PSI) 10 / (A:HYDRAULIC PRESSURE:2, PSI) 10 /  +

This is the reason i was convinced the system was additive!o_O But it makes no sense to be additive as i agree. But it would be nice if there was a total pressure variable!

My next idea is to just use 1 electric pump as this might solve this issue!
 
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Roy so your saying with engines off and auxiliary pump off the system always has a minimum of 750 PSI. And this is why the flaps for example will still operate at a very slow speed. So i need to make my hydraulic gauge read no less than 750 PSI at all times?
 
Fluid dynamics isn't additive when the source of the pressure is in parallel. It's just the way it is. As for the 750 psi... accumulators don't last forever, and in fact when you start to use the hydraulic system... the accumulator will lose pressure from the use.
 
I agree and thanks for the tip on the accumulators. Too bad there was not variable for it. i decided to use 1 electric pump and this made my coding easy and all is working good now.
 
Glad you have it good now.

Most hydraulic pumps have variable volume constant pressure output, this is why the pressure is the same at idle as at full RPM.
In the Lear there is one pressure gauge which comes off the common supply line. It does not care how many pumps are working, it just tells you what the pressure is in the line.
So there is no "total" pressure. If all pumps are working the pressure is 1500 to 1575, same with two or one. I would suggest you look at the two engine pressures and have the gauge read the highest.
They probably will be identical especially if you have min_pct_rpm_for_max_pressure set at idle or just below.

A simple example of how parallel or series works is two 1.5 volt batteries. Connect them in parallel and the voltage is 1.5, connect them in series like the positive terminal of one is connected to the negative terminal of the other, then voltage is additive at 3 volts. You want hydraulic systems to always have the same pressure so they are in parallel.

Accumulators are there to smooth out the pressure when a service is activated. They usually, like the Lear, have a nitrogen or air charge, which is displayed on a skin gauge near the accumulator.
If the accumulator is properly charged it will read say 750 psi on the ground with no pumps running. That pressure is what is pushing a piston in the circuit and the piston is at the end of its stroke (can't go any further).
When the system pressure is at 1500 psi the skin gauge would read 1500. The piston has been pushed back into the accumulator by system hydraulic pressure. When a service is operated, the accumulator provides an immediate source of pressure energy. When the engines are stopped and the electric pump is off, normal hydraulic seepage will cause the indicated hydraulic pressure to drop to zero after a short time. The piston has still got 750 charge, but has bottomed out and so is not providing pressure to the system. Before that happens the accumulator residual pressure will operate flaps etc.

Emergency accumulators are a different animal. They are charge with air and, following a complete hydraulic failure, their pressure is released into the system or relevant hydraulic system line. For example, if the Lear has a total hyd failure, the gear is blown down by air. In normal usage, the emergency accumulators do nothing.

Roy
 
Roy,
thanks for the good explanations of the accumulator. I wanted to ask here.

Can you tell me some time how long the accu would store the pressure without any usage??
And how long i could use the ailerons, elevator or other?
Of course it depends on the aircraft and couldn't be very exact! Only to get a bit an idea!
My hydraulic panel is for a B727.
In the AOM is spoken from "precharge" is 2000 psi. This means the pressure gauge shows minimum 2000 psi without hydraulic pressure from a pump.
It's the same as above with the 750 psi?

Edi
 
Edi,
How long it takes before pressure drops will vary between aircraft according to how many items are connected, so I can not give you an answer for the 727.
If the AOM does not list it I doubt anyone knows.
The 2000 psi probably comes from the nitrogen charge. If it was supplying hydraulic pressure it would stop once the pressure reaches 2000 at the accumulator gauge. I guess that is the same as the 750.
If you did not have an accumulator the working pressure would drop every time a service is operated and probably set off the low pressure warnings. The F-4 had accumulators for the utility hydraulics, pre-charged to 1000 psi, normal working pressure was 3000. When you dropped the gear the pressure drop was usually enough to light the warning captions.
The Hunter had power control accumulators and the Pilot's Notes stated that after a failure there may be enough reserve pressure for 3 full reversals of aileron and elevator. It also said that if no control movement was made the accumulator pressure would not be maintained due to normal component seepage.
Roy
 
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Yes thanks for the detailed info on how hydraulic and accumulators work. The tech manual said i have a couple of tanks in the nose of the aircraft and i think it said a type of gas, maybe nitrogen as you said. Not sure if i want to have the gauge read 750 PSI and then try to write a long and crazy code to have this drop if something is used. So i will just let the gauge read zero when the engines or auxiliary switch is off.
 
DG, guess I did not explain clearly what I meant by the gauge that shows 750psi accumulator pressure.
The gauge is at the back of the airplane in or by the Hydraulic Service Access Panel. There are two accumulators with pressure gauges there.
The gauges show the pressure of gas in the accumulators, not hydraulic pressure. They are checked on a full external inspection.
Your decision to show zero hydraulic pressure on the cockpit gauge when all pumps are off is correct.
Roy
 
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