What sorts of hydraulic pumps are used in aircrafts to activate the control surfaces and other areas operated by hydraulic power? Does aircrafts use Hydrostatic pumps? If yes which type of hydrostatic pumps does it use?

Thankfully
George

A/C and D/C driven pumps.

Basic rundown:

--Engine driven from the AGB

--Electric motor driven ( 3-phase AC being the vast majority )

--Pneumatically driven from bleed air ( usually used as "demand" pumps )

--PTU's ( basically a hydraulically driven, hydraulic pump )

--Ram Air Turbine ( emergency use )

Pumps themselves are usually of the variable displacement piston type, and not all A/C have all the above types of pumps.

OK thanx for the information on how they are driven but would like to know what different types of pump are used.

Regards
George

Just off the top of my head: Piston, Gear, Gerotor......

I'm pretty sure most in air transport use are of the variable displacement, piston type.

Usually variable displacement multiple piston pumps. The output volume is regulated by a swash plate increasing or decreasing the stroke of the pistons and is in turn moved by a control piston, which watches the pressure. The idea is to keep the pressure constant, not matter what the load is.
Another typte usually used in auxillary systems are multiple piston pumps with a pressure relief valve to control the pressure output. Normal output pressure: 3000 psi

Typical manufacturer: Vickers

Jan

A couple of other manufacturer's are Abex and Sundstrand.

What exactly is your definition of a hydrostatic pump? A hydrostatic SYSTEM or transmission is defined as closed circuit tankless or resevoirless system that uses the variable output of the pump to vary the power transmitted. Aircraft systems even though they mostly use variable displacement pumps are not considered hydrostatic because they are in effect open systems that incorporate resevoirs.

Dl757Md

Variable displacement piston pumps normally used,developing approx 3000psi output pressure.
regds
MEL

Dl757md

What I actually meant by a Hydrostatic pump is that the one which positively displaces the hydraulic fluid ie a definite amount of fluid will be ejected per revolution of the pump shaft like Gear, vane or piston pumps. And not the ones like Centrifugal pumps which are Hydrodynamic or non positive displacement in nature.

Regards,
George

Santosh

I understand now. Yes most if not all hydraulic pumps on aircraft positively displace fluid by means of a gear, gerotor,or piston. I'm trying to think if I've ever come across a vane type hydraulic pump in aviation but I'm coming up blank. Perhaps large older piston aircraft or GA use them. Most of my experience is with modern commercial aircraft and the system pressure (3000psi) is just too high for a vane pump. As for centrifugal pumps the Vickers engine driven pumps used on large turbofans have a centrifugal impeller mounted in the inlet port that acts as a boost pump to prevent cavitation of the main piston pump. That is the only aviation application of a centrifugal hydraulic pump that I'm aware of yet I'm certain that there are others.

When I started at Delta I overhauled hydraulic pumps in the component shop.
It was totally boring repetitive work but it did have some interesting aspects; for instance we would lap the cylinder block and valve plate rotating surfaces to within 16 millionths of an inch from flat. After lapping the surface on a lapping machine you polish it to a mirror finish on a polishing plate. You then put the part under a monochromatic light and put an optical flat on it (basically a precisely flat optical glass). Bands of light and dark run across the face of the part and if they are straight the part is flat within 1 millionth of an inch. If the bands are curved and you can intersect two points on the same band and a point on an adjacent band with a straight line then the part is flat within 16 millionths of an inch. Like I said pretty boring.

Dl757Md

Do they use Gerotor pumps in Airbus aircrafts, and can you point me out to any sites where I can view the picture, diagram or working of Gerotor pump as well as other pumps used in aviation?

Thanx
George

I don't know about gerotor pump use on Airbus. I can't recall the pump but I've seen the gerotor used as a step-up or 1st stage pump for a main or 2nd stage piston pump.

I did a quick google search and found this sitehttp://www.gmc.ulaval.ca/cours/17931/Fphd/SectAWht/Pumps.pdf

Cheers
Dl757Md

Dl757Md
Thanx very much for the link.It was helpful.

Is centrifugal pumps used to pump the fuel and what are the specifications for the pumps used.

Thanx
George

What type of hydraulic fluid is used in aircrafts?

Thanx
George

Modern Commercial Aircraft use Skydrol LD4 under BMS3-11 spec.Which is a phosphate ester based Fluid.
Others include Mineral based fluid like MIL-OH-5606,also used in L/G oleos of B737s.
regds
MEL

Fluid types:

1.MIL-H-5606, older mineral base hydraulic fluid. Still used in struts.
2.Skydrol
3.A lot of military aircraft use MIL-PRF-83282 in their hydraulic systems.

As far as pumps concerned, the majority of hydraulic pumps are based on the piston, variable displacement "stratopower" type.

Oh yeah, dont forget the good ole hand pump!!

Hi, guys, I just got on after several weeks of absense. I am glad to see many of you mentioned Vickers pumps - I have worked at Vickers (now Eaton Aerospace) for 26 years, designing pumps, motorpumps, PTU's, etc.

Most of you are correct - all engine pumps and electric pumps are variable dsplacement inline piston types. The older DC-9, 727, 737 and MD-80 engine pumps are variable displacement bent-axis piston types.

Smaller aircraft - most notably Cessna bizjets - use fixed displacement gear pumps up to 1500 psi or so.

I have not seen vane pumps in hydraulics, although we use it for fuel - for example the GE T700, PW300 series and the TFE731 series use our vane pumps, among others.

Commercial aircraft use phosphate ester fluids - which include Skydrol and Aerojet brand names. They comply with Boeing's BMS3-11, SAE's AS1241, etc. Military aircraft use MIL-H-5606, MIL-H-83282 and MIL-H-87257 (the newest). The latter 2 are synthetic hydrocarbons, somewhat fire-resistant, similar to Mobile-1 engine oil. The 5606 is the older hydrocarbon and is limited to 275F maximum temperature.

Someone mentioned centrifugal and gerotors. Centrifugals at these high pressures (3000 psi) are not practical, as they would require a very large wheel diameter (when operated at 3500-4000 rpm). When full flow is not required, the efficiency gets very low, generating excessive heat at a high turn-down ratio.

Gerotors are not efficient either - they are used primarily as scavenge pumps, removing a metered amount of case flow at 300 psi. You guys working on our pumps will find gerotors buried deep within our AC motorpumps used in the 747, 757, 767, and 777.

Finally, Sundstrand is not really a player in hydraulic pumps - they have some of their pumps on their RAT's, and of course inside their constant speed generators. However, we and Abex (Parker) supply many of their RAT pumps.

If you have any more questions, just ask away!

Pete

Dl757Md, thanks again for the info about the hydraulic pumps, I was going over this stuff in class. Great info from the others too. At least this a good place to get info too.

Delta-flyer

Sir thanx very much for the detailed explanation regarding the hydraulic pumps and fluids used.

Thankfully,
George

Its Interesting to note that although many options are available in Aviation for Hydraulic pumps,only a certain few are used frequently.
regds
MEL

Do aircrafts have an Accumulator in the hydraulic circuit? If so what type of an accumulator is used?

Thanx,
George

The ERJs have two hydraulic accumulators. One is for the main door and landing gear free fall assistance and the other one is for the emergency brakes.
The BAe146/RJ has two accumulators. One for each hydraulic system. An optional third accumulator supplies the airstair system, if installed.
The CRJs use one accumulator for each hydraulic system and two(?) brake system accumulators.

All above mentioned accumulators are of the piston type.

Troubleshoote-
The piston actually acts as a separator between the hydraulic fluid and the loading system inside the accumulator.Right? So is the piston spring loaded or gas loaded.

George

The accumulators which I described in my last answer are of the piston type with a nitrogen precharge.

Thanx, That answer was what I was looking for. BTW where can I fine diagrams of Hydraulic circuit in various aircrafts?

George

Douglas and Airbus like accumulators of the bladder type ( a spherical housing with an elastic aballon inside).
The balloon is connected to the respective hydraulic system, while the space between the balloon and the housing is filled with pressurised nitrogen.

Boeing prefers the sliding piston type accumulators.

Jan

Quoting Santhosh (reply 25): BTW where can I fine diagrams of Hydraulic circuit in various aircrafts?

George,I have a few schematics if you need one but on the B737-200/300/400/500/700/800/900 Only.
Tell me I could scan & Email it accross.
regds
MEL

Quoting HAWK21M (reply 27): George,I have a few schematics if you need one but on the B737-200/300/400/500/700/800/900 Only. Tell me I could scan & Email it accross.

MEL-Thanx very much for the offer. It would be very helpful if you could take a photocopy of those schematics and sent over in my address. If that’s difficult for you then never mind you can e-mail me.

Thankfully
George

Quoting Santhosh (reply 25): BTW where can I fine diagrams of Hydraulic circuit in various aircrafts?

Try this http://www.b737.org.uk/hydraulics.htm

747NUT- Thanx for the link. It does explain about the circuit a bit.

Regards,
George

Quoting Santhosh (reply 28): MEL-Thanx very much for the offer. It would be very helpful if you could take a photocopy of those schematics and sent over in my address. If that’s difficult for you then never mind you can e-mail me

Is your Address on the list...I'll mail them to you,in a few days.
regds
MEL

MEL! Yes my address is on the list.Sorry for the delay in reply,was out for an Industrial Visit to Bangalore last week.

Regards,
George

Santhosh,

Detailed schematics of many commercial aircraft hydraulic systems are in SAE document AIR5005. Here's a link .....

http://www.sae.org/servlets/productDetail?PROD_TYP=STD&PROD_CD=AIR5005

Pete

Quoting Santhosh (reply 32): Yes my address is on the list

You want the Hydraulic or Electrical Schematics.
regds
MEL

Hi at all
found a drawing from the EDP at a A310/A306.


Ingo

Quoting Delta-flyer (reply 33): Detailed schematics of many commercial aircraft hydraulic systems are in SAE document AIR5005. Here's a link .....

Thanx very much for the link Sir.

Quoting HAWK21M (reply 34): You want the Hydraulic or Electrical Schematics.

If there aren’t too many papers to be copied then I would like to have both or else just the Hydraulics would do. It’s just for me to keep as a hardcopy for Reference.Hope I am not troubling you too much.Thanx a lot MEL

Quoting IFixPlanes (reply 35): Found a drawing from the EDP at a A310/A306.

Thanx for the A310 Schematics.

Regards
George

Quoting Santhosh (reply 36): If there aren’t too many papers to be copied then I would like to have both or else just the Hydraulics would do

I'll get the Prints of both for you from the Mx Hangar.And I'll mail it to you.
regds
MEL

Quoting HAWK21M (reply 37): I'll get the Prints of both for you from the Mx Hangar.And I'll mail it to you.

Despatched.
Tell me when you get it.
regds
MEL

While reading an SAE document on aircraft Hydraulics I came across the following

Boeing 747-100/200/300 has 4 Air Driven Pumps and 1 Power Transfer unit as Back up pumps so what are these air driven pump and power transfer unit?

George

Never heard of a PTU installed on a B747-100/200 but the -300 may have one. The air driven pumps (ADPs) are housed in the pylons. There are the same part number pump installed on the engine. The pumps are mounted on a air turbine unit which uses aircraft bleed air to turn the pump. The ADPs (1 per system) become a second source of hydraulic power in the system and supplement the engine pumps during high demand usage. The output is equivelant to the engine pumps.

A PTU is a hydraulic driven hydraulic pump. The PTU is plumbed into the 2 systems. One of the systems id the "drive" system and the other is the "demand" system. The 3000 psi produced by the drive system will turn a hydraulic motor which is on a common shaft with a hydraulic pump. This pump is normally a lower output pump and is usually automatically started in the event of a hydraulic failure. Again, I don't think the B747 has one.

can anyone explain me the difference of variable displacement piston pump and stratopower pump.

Regards.
Skywalker92

Quoting skywalker92 (Reply 41): can anyone explain me the difference of variable displacement piston pump and stratopower pump.

Stratopower is a manufacturer that builds variable displacement piston pumps.

Here is a teardown of a small one.
http://www.rtftechnologies.org/gener...ydraulic-pump-stratopower-65w.html

thanks larshjort  

unloading valve are using in fixed displacement type pumps and what sort of valve we accommodate in variable displacement type pumps?

Skywalker92, sounds like you are exploring the differences between open centre and closed centre had systems...
There's a good resource here: http://daerospace.com/HydraulicSystems/index.php
...for anyone who's interested, researching, or just doing homework!?  
The creator of this site teaches a course based on the material he makes freely available here, that normally costs $2000 per head, so is nice of him! (an ex-Boeing / Learjet hyd systems expert)

Regarding unloading valves skywalker, these are typically going to be used on engine driven pumps during engine startup, usually with variable displacement pumps. Unloading valves short circuit pressure and suction to unload the pump, but can't be used for long or you get overheating. There are also EDVs which are better: engine depressurisation valves, which de-stroke the compensator swashplate to unload the pump, for the same reason. You don't want the pump bogging down the engines on startup. Variable displacement pumps are used in 'closed centre' systems, and don't use a relief valve except for overpressure instances. (There's sometimes one on the high-pressure filter)

Then there are relief valves, for constant displacement pumps - your car's power steering will have this, as will the garbage truck which picks up your rubbish - constant displacement pumps are normally 'open centre', and are typically lower power, less complex systems. If run continuously, open centre systems make a lot of heat, as they continuously dump back to tank with no work to do, so usually need a radiator of some sort. In an open centre system the pump runs until it encounters resistance and builds enough pressure to crack the relief poppet open. The relief valve stays open until there is a new flow demand which drops the pressure again and redirects flow to the consumer.

For aircraft there are numerous other types of valves for different purposes including firewall shut-off valves, pressure maintaining valves, priority valves, blocking valves etc. etc.

As for hydrostatic, these are best thought of as continuously variable hydraulic transmissions, these are beginning to become prevalent in EHMA-actuators...

Then there are variable RPM constant displacement smart-pumps, but that's too complex for here...

Thanks a lot wingscrubber...
your explanation is more than enough....

I know it's of limited value here, but if you're curious about hydraulic architecture on the KC-135 or C-17 let me know! We've got an assortment of stuff on both.