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Metjetceo
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A320 Hydraulic Pumps

Thu Aug 07, 2014 12:46 pm

Why would Airbus design the hydraulic pumps on the A320 in a manner that they are so loud within the cabin during departure and arrival, as opposed to other airliners where you dont hear them? I used to think it was a motor opening/closing the baggage doors.
 
travelavnut
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RE: A320 Hydraulic Pumps

Thu Aug 07, 2014 1:35 pm

You mean the 'Bus Barking? IIRC those are not the hyd pumps but the PTU's (Power Transfer Units) that transfer power between the different hydraulic systems in case of a pump failure or during high demand of the system.

I don't know why they are so loud though, sorry.
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strfyr51
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RE: A320 Hydraulic Pumps

Thu Aug 07, 2014 5:07 pm

The noise is because the PTU is located at the top of the Wheel well right beneath the floor.
They could solve that be relocating it to the Keel Beam area but they'd have to relocate something else
So it might not be any better for the airplane.
 
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tb727
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RE: A320 Hydraulic Pumps

Thu Aug 07, 2014 5:22 pm

Has anyone noticed that on the 321 it isn't as loud/can't hear them at all? I was on an NK 321 a month or so ago and was expecting to hear it since I was right over the mains but didn't really hear them barking. It's either that or I'm tone deaf now in that frequency from years of Learjet and Boeing "B" Hydraulic pump hearing abuse.
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kcrwflyer
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RE: A320 Hydraulic Pumps

Thu Aug 07, 2014 7:16 pm

I hear it more during single engine taxi than any other time.
 
Dalmd88
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RE: A320 Hydraulic Pumps

Thu Aug 07, 2014 7:29 pm

Quoting strfyr51 (Reply 2):
They could solve that be relocating it to the Keel Beam area but they'd have to relocate something else

They could relocate it completely outside of the airframe on the top of the tail, it would still be heard by everyone. That is the loudest pump in all of aviation. When one is turned on in our four bay hangar everyone knows it. None of the Boeing or McD aircraft are anywhere near as loud. The only thing louder is the A320 Rat test.
 
Woodreau
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RE: A320 Hydraulic Pumps

Fri Aug 08, 2014 12:01 am

You aren't hearing the hydraulic pumps. You're hearing the PTU which transfers hydraulic pressure between the green and yellow hydraulic systems. The only two electric hydraulic pumps on the aircraft are the blue and yellow pump, you don't hear these pumps. The blue one runs whenever an engine is running and the yellow one is normally controlled manually by the flight crew although there are some times it will run automatically (associated with ground crew operations with the cargo door)

If the crew does it right you'll never hear the PTU during the entire flight except at the end for 2-3 seconds after the left engine is shut down and it's trying to equalize the pressure between the green and yellow systems.


The hydraulic pump on an EMB-145 is pretty darned loud though.

[Edited 2014-08-07 17:03:22]
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prebennorholm
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RE: A320 Hydraulic Pumps

Fri Aug 08, 2014 12:12 am

Quoting tb727 (Reply 3):
Has anyone noticed that on the 321 it isn't as loud/can't hear them at all? I was on an NK 321 a month or so ago and was expecting to hear it since I was right over the mains but didn't really hear them barking. It's either that or I'm tone deaf now in that frequency from years of Learjet and Boeing "B" Hydraulic pump hearing abuse.

There is no technical difference in this respect within the 320 family. But there are wide variations how much barking we passengers hear.

Those power transfer units (PTUs) provide hydraulic power to hydraulic lines which would otherwise be unpowered. The 320 family does not power all lines directly from each engine.

A PTU is in layman's terms a hydraulic motor, powered by a hydraulic line, pulling a hydraulic pump which powers an otherwise unpowered line. So when on the ground only one engine is running, and hydraulic power is used for wheel brakes, nosewheel steering, control actuator testing, spoiler testing or whatever, then the 320 barks. But if all hydraulic actuators are idle while only one engine is running, then it doesn't bark.

You don't hear a 330 barking because it powers all hydraulic lines from each engine. The 330 probably also have PTUs, I don't know. But they will only bark in case of some hydraulic failure.

We passengers of 21st century are maybe getting too sensitive when we hear a sound unrelated to a spinning engine. Maybe we should bring back the Caravelle for a while? Passengers well under my age would probably be scared to death when a Caravelle slams its main wheels up into locked position. They would think that a bomb exploded in the baggage compartment.
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roseflyer
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RE: A320 Hydraulic Pumps

Fri Aug 08, 2014 12:36 am

The 737 actually has a very similar power transfer unit that uses power from one hydraulic system to power the other. It is also terribly loud. The difference is that it does not come on when one engine is shit down. The 737 hydraulic system is configured differently so that if one engine is off, there is an electric pump for one system and the engine driven pump for the other. In addition the power transfer unit would only come on if there was a simultaneous high demand operation with the system low on pressure like deploying the slats. Airbus hydraulic architecture has the power transfer unit operating more frequently and single engine operations on the ground can activate it. This is due to the way the system is designed to handle the different demands on the ground.
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Starlionblue
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RE: A320 Hydraulic Pumps

Fri Aug 08, 2014 2:53 am

Quoting prebennorholm (Reply 7):
We passengers of 21st century are maybe getting too sensitive when we hear a sound unrelated to a spinning engine. Maybe we should bring back the Caravelle for a while? Passengers well under my age would probably be scared to death when a Caravelle slams its main wheels up into locked position. They would think that a bomb exploded in the baggage compartment.

Haha true!

If you want the contemporary bomb-in-the-luggage compartment experience I can recommend the overwing seats in a CRJ. Massive SLAMMMM and it feels like a giant took a mallet to the floor from underneath.

Quoting Roseflyer (Reply 8):
The difference is that it does not come on when one engine is shit down.

Best typo of the day. 
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N243NW
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RE: A320 Hydraulic Pumps

Fri Aug 08, 2014 5:31 am

Quoting Woodreau (Reply 6):
The hydraulic pump on an EMB-145 is pretty darned loud though.

You aren't kidding. I hate that thing. It's almost tolerable when you're just sitting there or going in a straight line at a constant speed, but the second the captain hits the brakes or turns the tiller, all aural hell breaks loose.
B-52s don't take off. They scare the ground away.
 
diverted
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RE: A320 Hydraulic Pumps

Sat Aug 09, 2014 6:34 pm

the Q400 does the same; super loud and obnoxious during taxi. The barking is a great way to describe it
 
wingscrubber
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RE: A320 Hydraulic Pumps

Sat Aug 09, 2014 8:05 pm

Quoting Woodreau (Reply 6):
The only two electric hydraulic pumps on the aircraft are the blue and yellow pump, you don't hear these pumps.

You sure about that? I'm sure you can hear the yellow sys EMP after engines are shut down. Its the yellow sys EMP which is driving the PTU after engines are shut-down at the gate.

Quoting prebennorholm (Reply 7):
Those power transfer units (PTUs) provide hydraulic power to hydraulic lines which would otherwise be unpowered. The 320 family does not power all lines directly from each engine.

Not strictly correct, the PTU is a backup in case of engine failure to allow gear retraction via yellow sys hydraulics.

Quoting prebennorholm (Reply 7):
But if all hydraulic actuators are idle while only one engine is running, then it doesn't bark.

There is constant quiescent leakage in the system, the PTU will always 'cog' while supplied with pressure from yellow sys as green sys servo-actuators constantly leak fluid back to return(reservoir), the only time the PTU goes completely quiet is when yellow sys EMP is switched off.
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wingscrubber
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RE: A320 Hydraulic Pumps

Sat Aug 09, 2014 8:39 pm

Quoting metjetCEO (Thread starter):

Why would Airbus design the hydraulic pumps on the A320 in a manner that they are so loud within the cabin during departure and arrival, as opposed to other airliners where you dont hear them?

The pump/PTU noise is just a side-affect of the design, the systems architecture is driven by redundancy, and the pump/PTU size is driven by the potential cumulative system demand from the flight controls and the landing gear.

The 'barking dog' noise you hear from the PTU is caused by the rapid acceleration/deceleration of the PTU rotor as the system pressure sawtooths - PTU speed ramps up until the pressure is equal and then stops. Internal leakage in the green system will cause the pressure to drop off again until the pressure balance accross the PTU causes it to kick-on again. It's a completely fluid-dynamic effect, it's not done by any clever electronics or software, it's just hydraulic force-balancing - PTUs get hot when kicking on and off like that though, the constant work on the fluid produces a lot of heat!

The electric motor pumps themselves are audible too, but as a high-pitched whine, they are constant speed and so don't bark like the PTU.

The main reason why the A320 PTU noise is so prevalent is because there is no EMP in the green system, it's in the opposing yellow system, and so the PTU(which is bi-directional) always runs when LH engine is off and either RH engine or the EMP are on. It's just a quirk unique to A320. Other aircraft might have the EMP in the same system as the landing gear, and use a uni-directional PTU instead (Citation X for example) so you won't hear it run as often. Others like the CRJs just forgo the PTUs altogether and add extra EMPs instead. To compare them all you really need a copy of AIR5005! There are many schools of thought on hydraulic system redundancy, no two airframers do it quite the same way.

[Edited 2014-08-09 13:40:50]
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longhauler
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RE: A320 Hydraulic Pumps

Sun Aug 10, 2014 7:17 pm

Quoting wingscrubber (Reply 12):
You sure about that? I'm sure you can hear the yellow sys EMP after engines are shut down. Its the yellow sys EMP which is driving the PTU after engines are shut-down at the gate.

The only reason the Yellow electric hydraulic pump would be powered at the gate is to open/close the cargo doors, and it is only running during the operation of the doors. Otherwise, all three hydraulic systems are powered down when the aircraft is at the gate, and only power up again during engine start.

Quoting wingscrubber (Reply 12):

Not strictly correct, the PTU is a backup in case of engine failure to allow gear retraction via yellow sys hydraulics.

Only the green system powers landing gear hydraulics. And ... the only backup is a manual gear extension. (never retraction).
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Tristarsteve
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RE: A320 Hydraulic Pumps

Sun Aug 10, 2014 8:00 pm

Quoting longhauler (Reply 14):
Only the green system powers landing gear hydraulics.

Agreed, but I think what he means is that if the Nbr 1 engine fails on take off, the PTU will pressurise the Green system and allow landing gera retraction, powere by the yellow EDP.
 
ual777
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RE: A320 Hydraulic Pumps

Mon Aug 11, 2014 4:36 am

Quoting N243NW (Reply 10):

You aren't kidding. I hate that thing. It's almost tolerable when you're just sitting there or going in a straight line at a constant speed, but the second the captain hits the brakes or turns the tiller, all aural hell breaks loose.

Taxiing on engine 1 eliminates the issue. If we know its going to be a long taxi, then we will wait until after disconnect and spin 1.
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AA737-823
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RE: A320 Hydraulic Pumps

Mon Aug 11, 2014 8:51 pm

For the record, the 737's PTU pump makes a virtually identical noise. You just only hear it when you run the PTU test, because it never otherwise operates!!
 
masi1157
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RE: A320 Hydraulic Pumps

Tue Aug 12, 2014 7:18 am

Quoting Dalmd88 (Reply 5):
They could relocate it completely outside of the airframe on the top of the tail, it would still be heard by everyone.

Sad but true. The "solution" to that noise problem is sitting here on my desk since 20 years. It consists of 4 hydraulic silencers, each the size of a beer can, that would have added quite a bit of weight and required repressurization with nitrogen every couple of flights. For the airlines that was not viable, so they (and we) now live with that barking.


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longhauler
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RE: A320 Hydraulic Pumps

Tue Aug 12, 2014 2:03 pm

Quoting Tristarsteve (Reply 15):
Agreed, but I think what he means is that if the Nbr 1 engine fails on take off, the PTU will pressurise the Green system and allow landing gera retraction, powere by the yellow EDP.

What you say is correct, and quite honestly ... something I never considered on the A320 series when I flew them. On the A320, V1 and Vr, are usually within a couple knots of each other, and gear is retracted about 3 or 4 seconds after Vr. One would have to have an engine failure during that narrow slice of time for the PTU to perform that function ... and, the engine sould have had to have "siezed" as when free turning or when on fire, it's still producing hydraulic pressure.

The only time I have ever heard of, or experienced an engine failure to the point of siezing at that time, is in the simulator.

I only mentioned this though, as on another type in our fleet I flew, there was a note in the hydraulic architecture stating that the PTU was for the function he stated. (gear retraction on engine failure after take off). I thought maybe he had his types mixed ... but fair ball ... it would work on the A320 as well.
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roseflyer
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RE: A320 Hydraulic Pumps

Tue Aug 12, 2014 7:46 pm

Quoting AA737-823 (Reply 17):

For the record, the 737's PTU pump makes a virtually identical noise. You just only hear it when you run the PTU test, because it never otherwise operates!!

You will hear it if you lose an engine and are about to stall because of it. The PTU will put out the slats if approaching a stall due to loss of the engine that powers the B hydraulic system. It is rare, and if that is happening, you probably are hearing some other strange things too, like many people screaming.

Quoting longhauler (Reply 19):

What you say is correct, and quite honestly ... something I never considered on the A320 series when I flew them. On the A320, V1 and Vr, are usually within a couple knots of each other, and gear is retracted about 3 or 4 seconds after Vr. One would have to have an engine failure during that narrow slice of time for the PTU to perform that function ... and, the engine sould have had to have "siezed" as when free turning or when on fire, it's still producing hydraulic pressure.

The only time I have ever heard of, or experienced an engine failure to the point of siezing at that time, is in the simulator.

I only mentioned this though, as on another type in our fleet I flew, there was a note in the hydraulic architecture stating that the PTU was for the function he stated. (gear retraction on engine failure after take off). I thought maybe he had his types mixed ... but fair ball ... it would work on the A320 as well.

The FARs have strict engine out takeoff performance requirements. One of the requirements is to get the landing gear retracted in a specific amount of time in order to reduce drag for obstacle clearance. Rather than increasing engine thrust or limiting TOW, the designers find it easier to have a redundant method of retracting the gear. Similarly the 737 has a landing gear transfer valve due to the exact same takeoff condition. Slat extension and gear retraction require some significant redundancy in the hydraulic systems since losing one engine is essentially not allowed to have any impact on their operation according to the FARs.
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apodino
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RE: A320 Hydraulic Pumps

Thu Aug 14, 2014 8:08 pm

Quoting kcrwflyer (Reply 4):
I hear it more during single engine taxi than any other time.

Part of the reason for this is because if a single engine taxi on number 2 is being performed, the only way to get the green system powered is through the PTU, since the green system normally is only powered by an Engine Driven Pump on the Numebr 1 engine. If the single engine Taxi is on the number 1 engine, the sound you would normally hear would not be the barking dog sound of the PTU, but the high pitched sound of the Yellow System Electric Pump, since the Engine Driven pump that powers the yellow system is on the Number 2 engine.

Quoting AA737-823 (Reply 17):
For the record, the 737's PTU pump makes a virtually identical noise. You just only hear it when you run the PTU test, because it never otherwise operates!!

The only use for the PTU on the 737 is for autoslats and leading edge flaps at normal speed if System B is lost. The 320 makes much more use of the PTU.

Quoting prebennorholm (Reply 7):
You don't hear a 330 barking because it powers all hydraulic lines from each engine. The 330 probably also have PTUs, I don't know. But they will only bark in case of some hydraulic failure.

There are no PTUs on the 330. Interestingly enough, there are two Engine Driven Pumps on each engine on the 330. The Green system is powered by one on each engine, the Yellow is powered by one on the number 2 engine and the Blue is powered by one on the number 1 engine. Each system also has an electric driven pump, plus the RAT will power the Green System and a hand pump will power the Yellow System.

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