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Guest bruchpilot

Manual - wording misleading

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Guest bruchpilot

Hello,I find the Hydraulics Section of the Manual misleading in terms of wording. I still don't know much about the 747 but normally the term "Demand pumps" refers to the pumps that operate when the eninge driven pumps fail or there is aditional *demand*. This it should read:"Each hydraulic system is comprised of a hydraulic, reservoir, an engine driven pump, electrical demand pump (engine 2 and 3) or hydraulic driven demand pump (engine 1 and 4)"The term "engine driven demand pump" IMHO does not make any sense and so doesn't "Auxiliary Demand Pump". It should be either "Auxiliary Pump" (misleading because in this context it does not mean the No 4. AUX !!!) or "Demand Pump".GreetingsEdgar

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Edgar,While I may agree with you that using "auxiliary and demand" in combination makes little sense (redundant wording) I found the documentation crystal clear on the subject, I did not feel I was misled or somehow the documentation was less clear because of that. Minor issue IMHO.Michael J.http://www.precisionmanuals.com/images/for...argo_hauler.gifhttp://sales.hifisim.com/pub-download/asv6-banner-beta.jpg

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Guest bruchpilot

Michael,I agree with you that you can understand everything if you have a basic knowledge of how Boeing hydraulic systems work (e.g. from the the 737 or 767). But for everybody else there is just a mixture of misleading words and abreviations (e.g. ADP: Auxiliary Demand Pump (does not make sense) or Air Driven Pump (this way the abreviation is used with the 767 but here in the 747 it is only the case with engines 1 and 4)GreetingsEdgar

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Guest lou ross

Unfortunately there are a number of points where the manual is confusing, in error, or even contratictory. If you happen to understand (from real world experience)what the manual is trying to say, it is much easier to understand the manual as printed.

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I guess those not familiar with hydraulic systems might find the terminology a little confusing, however, if you read it thru a few times it makes perfect sense. From reading your post the confusion seems to center around the fact that using the terms 'Auxilary' and 'Demand' are one and the same. They are in fact auxilary AND demand pumps. They are auxilary in that they back up the primary engine driven pumps. The normal position of these pumps is 'auto' so that they work on demand or permanently in case of EDP failure. The importance here is that they can also be selected to the 'on' position so that they remain running and not operate on demand. If these pumps were just called 'demand' pumps then this would not cover the later case and could cause more confusion. I can see the potential for cofusion with the number 4 system as this has a position called 'aux'. The main difference is is that this powers a small separate electrical pump and is essentially only used for brake pressure for pushback and or towing operations.Considering some of the aircraft systems manuals I have read over the years these ones are very well written and illustrated.RgdsSteve

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Guest D17S

Just to provide a taste of tradition and comparison, in the case of the old 747-1/200s there are Engine Driven hydraulic driven pumps on all 4 engines and Air Driven hydraulic pumps also, in all 4 engine pylons. Operators have called the Air Driven hydraulic pumps "ADP"s since 1970. Also, on the -1/200s, there is always a small electric hydraulic pump mounted in #4 pylon to power the #4 hydraulic system (brakes) during ground ops. Operators have called this little guy the "AUX Pump" since the beginning. Sometimes I see a second AUX hydraulic pump installed in #1 engine's pylon as well. That would be called "#1 AUX pump."The only change I see with the -400 is that the #2 and #3 ADPs were replaced by electrical pumps . . and thank goodness for that. Those ADPs are not just hydro pumps. They are air-driven gearboxes and a real PITA to maintain. Here's the only real conundrum I can see. What are we going to call these "new" electrical pumps that replaced the inboard ADPs on the -400s. The other pumps already have names. The term "AUX" is already in for the small electrical pump installed in the #4(#1) hydraulic system(s). The term "ADP" (air driven pump) is in use for the pumps/gearbox assemblies installed in the #1 and #4 engine pylons. The term "Demand" is just a generic, functional description that covers both the ADPs for the outboard systems and the new electrical pumps (that replaced the ADPs) for the inboard systems. These are ALL

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Guest bruchpilot

Hello,okay, the part: "Each hydraulic system is comprised of a hydraulic, reservoir, an engine driven pump, electrical demand pump (engine 2 and 3) or hydraulic driven demand pump (engine 1 and 4)"Does not come from the manual but was a proposal. Of course it is wrong also. It should read:"Each hydraulic system is comprised of a hydraulic reservoir, an engine driven pump, electrical demand pump (engine 2 and 3) or bleed air-driven demand pump (engine 1 and 4)"Sorry for the confusion.

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Guest bruchpilot

By the way - can anyone tell me the meaning of the EICAS Message:HYD CONTROL 1,4 Manual says:Auto Control of hydraulic system demand pumps is inoperative.Why just 1 and 4? A special measure system for the ADPs?GreetingsEdgar

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Guest hangar744

Sam, you stated, that all -400's got their inboard ADP's replaced by electric pumps (by the way, they are called ACMP's) is not true. Take a look at United Airlines -400's, the entire fleet is operating with 4 ADP's. No trace of ACMP there.regards,delcomwww.nippoo.net

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"Sam, you stated, that all -400's got their inboard ADP's replaced by electric pumps (by the way, they are called ACMP's) is not true."Beat me to it, Delcom :) ... 4 ADP's seems to popular on P&W powered aircraft (perhaps because they have hydraulically powered reversers).Also, the automatic function of the pumps is not purely reliant on a drop in hydraulic pressure such as would be expected with engine pump failure and increased demand. The 744 also has a predictive function. For example, the 1&4 ADP's will run automatically when the trailing edge flaps are sensed to be in motion. Additional logic can be added to make the pumps run when the flaps are "out of up" (in flight).Edgar said:"This it should read:"Each hydraulic system is comprised of a hydraulic, reservoir, an engine driven pump, electrical demand pump (engine 2 and 3) or hydraulic driven demand pump (engine 1 and 4)"Edgar, what is a "hydraulic"? As you can see, we are all susceptible to errors in english. ;)Cheers.Q>

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