jeffry747
Topic Author
Posts: 907
Joined: Thu Jun 30, 2005 6:26 pm

### Hydraulic Fluid And The 757

As my crewmates and I were loading the rear belly of an outbound UPS 757 last night, we came across some cargo which sparked a discussion; 3 five gallon containers of Skydrol LD-4 fire resistant hydraulic fluid. They weighed in at 47 lbs. per can and were being shipped as COMAT (COmpany MATerial). We started pondering a few questions such as:

A) How much in U.S. dollars does this stuff cost? One person guessed \$100 per 5 gallon can, I guessed \$250 and one other guessed as high as \$500 per can. Which is the closest estimate?

B) How much hydraulic fluid does a 757 require to be operational?

C) Since the label marked it as fire resistant, does that make Skydrol LD-4 a "higher grade" hydraulic fluid than any other?

D) Why is hydraulic fluid so darn heavy?
C'mon Big B, FLY!

roseflyer
Posts: 9605
Joined: Fri Feb 13, 2004 9:34 am

### RE: Hydraulic Fluid And The 757

 Quoting Jeffry747 (Thread starter):A) How much in U.S. dollars does this stuff cost? One person guessed \$100 per 5 gallon can, I guessed \$250 and one other guessed as high as \$500 per can. Which is the closest estimate?

I've heard that skydrol can be up to \$40 per liter. I would think that \$500 is on the lower side of how much it costs.

 Quoting Jeffry747 (Thread starter):B) How much hydraulic fluid does a 757 require to be operational?

This is a rough guess, but I'll say 25 or so gallons.

 Quoting Jeffry747 (Thread starter):D) Why is hydraulic fluid so darn heavy?

I believe the high density is directly related to its performance. It is pressurized at 3000psi, so a denser fluid works better. I don't understand exactly why though.
If you have never designed an airplane part before, let the real designers do the work!

avioniker
Posts: 1100
Joined: Tue Jan 01, 2002 5:38 am

### RE: Hydraulic Fluid And The 757

Here's a little bit too much info for you. . . I've forgotten what the actual capacity is. Hawk, you out there???
http://www.757.org.uk/systems/sys7.html

One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533

HAWK21M
Posts: 30007
Joined: Fri Jan 05, 2001 10:05 pm

### RE: Hydraulic Fluid And The 757

 Quoting Avioniker (Reply 2):I've forgotten what the actual capacity is. Hawk, you out there

From what I remember something around 25litres for LH & RH reservoir each & 13 litres for CTR Reservoir.
Not sure about the Fluid trapped in the line.Would need to check it up.
regds
MEL
I may not win often, but I damn well never lose!!!

jetmech
Posts: 2322
Joined: Wed Mar 29, 2006 2:14 am

### RE: Hydraulic Fluid And The 757

 Quoting RoseFlyer (Reply 1):I believe the high density is directly related to its performance. It is pressurized at 3000psi, so a denser fluid works better. I don't understand exactly why though.

The "LD" on the side of a can of Skydrol actually stands for Low Density! A 5 US gallon can is 18.925 litres, which according to Jeffry747, weighs 47lbs, or 21.354 kg. This gives Skdrol LD-4 an SG of around 1.128, which is a bit denser than water. I don't think there is any real relationship between the density a fluid it's suitability to high pressure, as all fluids by definition are incompressible. More important with respect to a hydraulic fluid would be the overall bulk modulus of the fluid.

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair .

fr8mech
Posts: 6855
Joined: Mon Sep 26, 2005 9:00 am

### RE: Hydraulic Fluid And The 757

Mel is correct on the reservoir quantities. I'd guess at least that much in the various systems. I wasn't able to find anything in the maintenance manual. But that kind of information is usually 'gee-whiz' type stuff found in training manuals.

I found an online source for LD4: 229.51 British Pounds per 5 Gallon drum. That's \$461.40 at current rates.
When seconds count...the police are minutes away.

roseflyer
Posts: 9605
Joined: Fri Feb 13, 2004 9:34 am

### RE: Hydraulic Fluid And The 757

 Quoting Fr8Mech (Reply 5):Mel is correct on the reservoir quantities. I'd guess at least that much in the various systems. I wasn't able to find anything in the maintenance manual. But that kind of information is usually 'gee-whiz' type stuff found in training manuals.

I don't know if anyone truly knows the exact volume of the system. It's pretty difficult to calculate the amount used by every actuator, every hose and every tube. Only once is the system ever filled completely from scratch, and that's in production. I don't think the system is ever completely bled in normal service although sections are.
If you have never designed an airplane part before, let the real designers do the work!

HAWK21M
Posts: 30007
Joined: Fri Jan 05, 2001 10:05 pm

### RE: Hydraulic Fluid And The 757

 Quoting Fr8Mech (Reply 5):I wasn't able to find anything in the maintenance manual. But that kind of information is usually 'gee-whiz' type stuff found in training manuals.

I checked the AMM found the Quantities correct as remembered.
However no mention on total system capacity.
Will def try & find out though.
regds
MEL
I may not win often, but I damn well never lose!!!

Tristarsteve
Posts: 3426
Joined: Tue Nov 22, 2005 11:04 pm

### RE: Hydraulic Fluid And The 757

Can't help you on B757, but I have just serviced a B777 hyd system, and beside the refill point was a placard with the quatities.

Left tank 42 lts system 159 lts
Centre tank 89 litres system 337 litres
Right tank 41 litres system 155 litres.

I don't see many B757 so MEL, go out and check.

HAWK21M
Posts: 30007
Joined: Fri Jan 05, 2001 10:05 pm

### RE: Hydraulic Fluid And The 757

 Quoting TristarSteve (Reply 8): don't see many B757 so MEL, go out and check

out here there are Two registered in the Country [VT-BDJ & VT-BDK] & Three from outside [AI leased B752,Ethiopean B752 & B752PF]
I'll try & check the docs.
regds
MEL
I may not win often, but I damn well never lose!!!

HAWK21M
Posts: 30007
Joined: Fri Jan 05, 2001 10:05 pm

### RE: Hydraulic Fluid And The 757

http://www.skydrol.com/pages/
I may not win often, but I damn well never lose!!!

rwessel
Posts: 2448
Joined: Tue Jan 16, 2007 3:47 pm

### RE: Hydraulic Fluid And The 757

http://www.skygeek.com/skydrol-ld-4-hydraulic-fluid-5-gallon.html

"Skydrol LD-4 Low Density Hydraulic Fluid - 5 Gallon
In Stock: 131 units. Ready to Ship: Today, Jan 21, 2013
International Orders
Part#: LD4-5GL
by Skydrol
Our Price: \$493.57"

wingscrubber
Posts: 815
Joined: Fri Sep 07, 2001 1:38 am

### RE: Hydraulic Fluid And The 757

 Quoting Jeffry747 (Thread starter):D) Why is hydraulic fluid so darn heavy?

Skydrol HD4, and Skydrol 5 are heavier, LD4 has a specific gravity slightly below that of water, HD4 and 5 slightly above. ALL are heavier than any of the red oils which are all lighter than water, Mil 5606, 87257 and 83282. Skydrol also has a higher thermal expansion coefficient.

 Quoting Jeffry747 (Thread starter):C) Since the label marked it as fire resistant, does that make Skydrol LD-4 a "higher grade" hydraulic fluid than any other?

'Fire resistant' is just marketing, the so-called 'flammable' red oils, 87257 and 83282 have equal or higher flash points, don't believe for a second that skydrol can't catch fire too. 5606 on the other hand is genuinely more flammable, but it's generally obsolete.

There's nothing 'high grade' about LD4, either skydrol brand or hyjet, it's just bog standard civil aircraft hydraulic fluid.
Skydrol 5 is supposed to be more advanced, IMHO the modern red oils are better, but the industry still loves skydrol for some reason, despite its numerous shortfalls. If I sound biased that's because I am.. for a reason too.
Resident TechOps Troll

Tristarsteve
Posts: 3426
Joined: Tue Nov 22, 2005 11:04 pm

### RE: Hydraulic Fluid And The 757

 Quoting Jeffry747 (Thread starter):B) How much hydraulic fluid does a 757 require to be operational?

Just found the following in a Boeing presentation (But can't quote it!!)

Hydraulic system total quantities in US gallons.

B767 L 18 C 43 R 20
B777 L 42 C 89 R 41
B787 L 21 C 49 R 20

Rgds

KC135Hydraulics
Posts: 441
Joined: Sat Nov 03, 2012 2:05 am

### RE: Hydraulic Fluid And The 757

Totally not regarding the 757, but I have KC-136 gee-whiz if you're interested!

Left HYD sys holds 21.5 gals, Right HYD sys holds 27.6 gals total. MIL-PRF-87257. A 55 gallon drum of this fluid costs the Air Force \$1,733.68. Yikes!
MSgt, USAF
KC-135R / C-17A Pneudraulic Systems Mechanic Supervisor

yeelep
Posts: 739
Joined: Mon Apr 04, 2011 7:53 pm

### RE: Hydraulic Fluid And The 757

Compared to Skydrol/Hyjet, that's cheap.

KC135Hydraulics
Posts: 441
Joined: Sat Nov 03, 2012 2:05 am

### RE: Hydraulic Fluid And The 757

 Quoting KC135Hydraulics (Reply 14):Totally not regarding the 757, but I have KC-136 gee-whiz if you're interested!

Of course the 136 is a typo. I can't seem to find the edit post function.
MSgt, USAF
KC-135R / C-17A Pneudraulic Systems Mechanic Supervisor

Starlionblue
Posts: 17897
Joined: Fri Feb 27, 2004 9:54 pm

### RE: Hydraulic Fluid And The 757

 Quoting KC135Hydraulics (Reply 16):Quoting KC135Hydraulics (Reply 14): Totally not regarding the 757, but I have KC-136 gee-whiz if you're interested! Of course the 136 is a typo. I can't seem to find the edit post function.

Goes away after an hour. You missed it by 6 minutes and 38 seconds.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

HAWK21M
Posts: 30007
Joined: Fri Jan 05, 2001 10:05 pm

### RE: Hydraulic Fluid And The 757

 Quoting Tristarsteve (Reply 13):Just found the following in a Boeing presentation (But can't quote it!!)

Interesting on the B767/787 numbers....I presume B764.
I may not win often, but I damn well never lose!!!

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