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Leak Check (air, Hydraulic, Oil, And Fuel)  
User currently offlineaerotech777 From United States of America, joined Aug 2009, 69 posts, RR: 0
Posted (1 year 3 months 2 weeks 17 hours ago) and read 4853 times:

Hi,

If I am not mistaken dry motoring drives N2/N3 to around 20%-25% N2/N3. I am assuming N1 will be driven at very low speed: may be 1% or 3% N1 ???

a) When performing leak check using dry motoring, the thrust reversers cowls or ducts are open. So based in your experience & A.M.M and if you are close to the core engine checking for leak, does the leak check represent a safety issue because the fan is sucking air through the core engine (T/R cowls open) especially for high or medium bypass engine?

b) Based on your experience & A.M.M, is dry motoring efficient to detect specific leak check: air, hydraulic, oil, or fuel ? I am asking this question because there is leak check using idle thrust or part power thrust. How often (approximate percentage) dry motoring leak check is efficient versus idle thrust or part power thrust leak check ?

c) How often (approximate percentage) leak checks (the 3 types of leak checks) are used in gate (line maintenance) or hangar ?
Does the leak check affects the turn-around time of the aircraft ?

Feedback appreciated.
Regards.

22 replies: All unread, jump to last
 
User currently offlineroseflyer From United States of America, joined Feb 2004, 9838 posts, RR: 52
Reply 1, posted (1 year 3 months 2 weeks 17 hours ago) and read 4847 times:

Why would dry motoring be used for a hydraulic leak check? Maybe for an engine driven pump change, but why not use electric pumps?


If you have never designed an airplane part before, let the real designers do the work!
User currently offlineaerotech777 From United States of America, joined Aug 2009, 69 posts, RR: 0
Reply 2, posted (1 year 3 months 2 weeks 17 hours ago) and read 4823 times:

Certain hydraulic components require driving the engine driven pump (for example EDP pressure filter, EDP case drain filter, ...etc.). In addition the electric pump provides low hydraulic flow (volume) compared to EDP especially for certain hydraulic users (for example slats if I am not mistaken).

User currently onlineyeelep From United States of America, joined Apr 2011, 671 posts, RR: 0
Reply 3, posted (1 year 3 months 2 weeks 16 hours ago) and read 4799 times:

Quoting roseflyer (Reply 1):

You answered your own question. Another reason is to confirm the ability to turn the EDP off by operation of the depressurization valve.

Quoting aerotech777 (Thread starter):
a) When performing leak check using dry motoring, the thrust reversers cowls or ducts are open. So based in your experience & A.M.M and if you are close to the core engine checking for leak, does the leak check represent a safety issue because the fan is sucking air through the core engine (T/R cowls open) especially for high or medium bypass engine?

Can't speak for a large engine like that on a widebody. But on a CFM-56, dry motoring doesn't really represent much of a safety issue unless you feel like sticking your arm in the fan.

Quoting aerotech777 (Thread starter):
Based on your experience & A.M.M, is dry motoring efficient to detect specific leak check: air, hydraulic, oil, or fuel ?

Hydraulic and pneumatic on the 737, oil and fuel will normally require idle/part power checks.

Quoting aerotech777 (Thread starter):
I am asking this question because there is leak check using idle thrust or part power thrust. How often (approximate percentage) dry motoring leak check is efficient versus idle thrust or part power thrust leak check ?

Dry motor 2%, idle 90%, part/high power 8%.


User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3708 posts, RR: 34
Reply 4, posted (1 year 3 months 2 weeks 11 hours ago) and read 4708 times:
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Which type of leak check to use is not optional. The method to use is specifed in the MM according to the particular maintenance action that has been carried out. Going over and above MM requirements achieves nothing additional.

[Edited 2013-09-15 19:15:43]

User currently offlineMender From United Kingdom, joined Feb 2004, 244 posts, RR: 0
Reply 5, posted (1 year 3 months 1 week 6 days 4 hours ago) and read 4444 times:

I'm trying to answer what I consider to be a theoretical question based on experiences such as performing a coke wash under strict safety procedures, for example being tethered to an immovable object. So please bear this in mind when reading my reply.

A). As far as the inlet is concerned, a CF6 is not capable of lifting you off your feet whilst being dry motored. Whilst it's a bit blowy, the fan by-pass air is not strong enough to harm you either.

B). Hydraulics - you can usually get full pressure from the EDP during dry motoring so it's a useful test.
Fuel & Oil - you should be able to find low pressure leaks but not high pressure leaks, you'll need above 80% power to find those.
Pneumatics - You can't find any pneumatic leaks by dry motoring the engine due to the starter noise and the fan by-pass air. However, you can usually configure the pneumatic valves to allow you to leak check most of the system using the APU, not the engine.

C). I'd say you are more likely to perform an idle leak check on the ramp than a dry motor whereas Hangar maintenance often perform a dry motor after an engine or component change before the perform the full ground runs. This is because the opportunity to perform ground runs is tighter.


User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3708 posts, RR: 34
Reply 6, posted (1 year 3 months 1 week 6 days ago) and read 4396 times:
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Quoting Mender (Reply 5):
B). Hydraulics - you can usually get full pressure from the EDP during dry motoring so it's a useful test.
Fuel & Oil - you should be able to find low pressure leaks but not high pressure leaks, you'll need above 80% power to find those.

That reminds me, on the 747 Classic/JT9 config there was a procedure to trace hydraulic internal leaks on a dry motor.

You put on as many air loads as possible (not the air driven hyd pumps) to drag the APU bleed air pressure down and then motor the required engine. The engine would get up to a max motoring speed of 12% N2 where the EDP was at max stroke delivering max hyd pressure and you just as many staff as necessary to feel the hyd component's in the affected hyd system. The component that got hot was the one with the internal leak.


User currently offlineKC135Hydraulics From United States of America, joined Nov 2012, 325 posts, RR: 0
Reply 7, posted (1 year 3 months 1 week 5 days 13 hours ago) and read 4340 times:

I work on KC-135s (CFM56) and I can tell you that for doing hydraulic leak checks, a motor is not as effective as an idle run. It will definitely give you 3000 PSI but the flow rate is significantly lower at max motoring as opposed to an idle run, and even an idle run doesn't give you the best GPMs.

I am not sure at what N1 % the EDP is providing its full 23 GPM capability but it certainly isn't at idle or even during a motor!

The nice thing about a C-17, on the other hand, is that it has two EDPs per engine. One is constantly on and the other is automatically initiated by the hydraulic system controller. During an idle run if the pressure drops below a certain threshold, the secondary pump kicks in and provides more than enough fluid flow to the hydraulic system to provide an excellent leak check and/or bleed. Of course, on the C-17 the AUX pumps work very well also, and typically can satisfy any leak or ops check requirement. The KC-135, on the other hand, has a worthless .75GPM aux pump which is barely sufficient to even perform a flight control check prior to takeoff.


User currently offlineMender From United Kingdom, joined Feb 2004, 244 posts, RR: 0
Reply 8, posted (1 year 3 months 1 week 5 days 4 hours ago) and read 4300 times:

Quoting KC135Hydraulics (Reply 7):
I can tell you that for doing hydraulic leak checks, a motor is not as effective as an idle run. It will definitely give you 3000 PSI but the flow rate is significantly lower at max motoring as opposed to an idle run, and even an idle run doesn't give you the best GPMs.

I'm well aware of that however if there is no hydraulic load on the system then no matter what the engine speed is, there will be no flow rate delivered by the hydraulic pump. Conversely if you have a large hydraulic load on the system you do not have a higher pressure delivered by the pump. What can happen is that you have a small leak (drip or stain) that goes unseen when you dry motor the engine, only to become blatantly obvious streaming leak when you run it at idle.

It is usually the pressure that finds any leakage point not the flow rate. If this was not true the maintenance manual would require you to perform a high power ground run to prove a system was leak free or you would be required to operate some form of hydraulic load.

In the case of the CF6 the maintenance manual only requires you to perform an idle run following an engine change (pre-tested engine). I've never know an engine to pass a hydraulic leak check at idle but then develop a leak at full power, however I have seen a few fuel leaks to show at full power but that is because the HP fuel system pressure increases with engine speed.


User currently offlineFr8mech From United States of America, joined Sep 2005, 5660 posts, RR: 15
Reply 9, posted (1 year 3 months 1 week 4 days 23 hours ago) and read 4268 times:

Quoting KC135Hydraulics (Reply 7):
I work on KC-135s (CFM56) and I can tell you that for doing hydraulic leak checks, a motor is not as effective as an idle run.

I no longer have access to a CFM AMM, but I seem to recall the CFM requiring many more leak checks at idle or flight idle. I want to say this was the engine that required a leak check for 'some component' at something like 80% percent N1, though that may have been the Tay.



When seconds count...the police are minutes away.
User currently onlineyeelep From United States of America, joined Apr 2011, 671 posts, RR: 0
Reply 10, posted (1 year 3 months 1 week 4 days 21 hours ago) and read 4242 times:

Quoting Fr8mech (Reply 9):
I want to say this was the engine that required a leak check for 'some component' at something like 80% percent N1
Accessory gearbox, transfer gearbox and AGB rotating seals require a part power leak check at 70% N1.


User currently offlineaerotech777 From United States of America, joined Aug 2009, 69 posts, RR: 0
Reply 11, posted (1 year 3 months 1 week 3 days 15 hours ago) and read 4108 times:

Thank you for your feedback

Quoting VC-10 (Reply 4):
Which type of leak check to use is not optional. The method to use is specified in the MM according to the particular maintenance action that has been carried out. Going over and above MM requirements achieves nothing additional.



I thought the AMM does not mention clearly the type of leak check specific for each fluid (fuel, oil, hydraulic, air): for example it does not say the dry motoring if good for hydraulic leak check, idle for oil leak check, or part power for fuel leak check,...etc. If it does, it will be nice if you can post an example from the AMM (Boeing, Airbus,...).

Quoting VC-10 (Reply 6):
That reminds me, on the 747 Classic/JT9 config there was a procedure to trace hydraulic internal leaks on a dry motor.

You put on as many air loads as possible (not the air driven hyd pumps) to drag the APU bleed air pressure down and then motor the required engine. The engine would get up to a max motoring speed of 12% N2 where the EDP was at max stroke delivering max hyd pressure and you just as many staff as necessary to feel the hyd component's in the affected hyd system. The component that got hot was the one with the internal leak.



I didn't understand this procedure. To my understanding, in order to get max motoring speed you have the reduce the loads (electrical and pneumatic) on the APU. Max motoring speed of 12% N2 seems low to me.

Regards


User currently offlineokie From United States of America, joined Jul 2003, 3198 posts, RR: 3
Reply 12, posted (1 year 3 months 1 week 3 days 11 hours ago) and read 4083 times:

Quoting aerotech777 (Reply 11):
I didn't understand this procedure. To my understanding, in order to get max motoring speed you have the reduce the loads (electrical and pneumatic) on the APU. Max motoring speed of 12% N2 seems low to me.

I get the idea that the test procedures were to rotate minimum N2 speed (12%) that could provide max pressure. (safety issue)
That is just a guess when reading areotech's reply.

Okie


User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3708 posts, RR: 34
Reply 13, posted (1 year 3 months 1 week 1 day 18 hours ago) and read 3989 times:
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Quoting aerotech777 (Reply 11):

I didn't understand this procedure. To my understanding, in order to get max motoring speed you have the reduce the loads (electrical and pneumatic) on the APU. Max motoring speed of 12% N2 seems low to me.

I meant the max motoring speed of the engine would be 12% because of all the air that is being bled off by the additional air loads on the pneumatic system. The air that was left for the starter motor could only produce 12% N2. Normal max N2 motoring speed on the starter with no additional air bleeds was 22-23%.

The aim of the test was turn the engine just fast enough to get the hyd EDP to just be able to manage to deliver full hyd press and then by using the Flt Control Hyd Isolation Valves deduce what part of the hyd system couldn't maintain 3000psi. Once you had identified whether it was in the tail or wings or not in the Flt controls you could dispatch you staff to feel the relevant hyd components to feel which one was hot.

( I admit I left some of the process out in my earlier description but it was over 25 yrs since I last performed this check)


User currently offlineHAWK21M From India, joined Jan 2001, 31712 posts, RR: 56
Reply 14, posted (1 year 3 months 1 week 1 day 18 hours ago) and read 3987 times:

Quoting VC-10 (Reply 13):
Once you had identified whether it was in the tail or wings or not in the Flt controls you could dispatch you staff to feel the relevant hyd components to feel which one was hot.

Amp-Clamp method works better.....



Think of the brighter side!
User currently offlinevc-10 From United Kingdom, joined Oct 1999, 3708 posts, RR: 34
Reply 15, posted (1 year 3 months 1 week 1 day 15 hours ago) and read 3954 times:
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I've no idea what the 'Amp-Clamp' method is. The method descibed is a Boeing MM procedure that needs no equipment apart from access equpt.

User currently offlineMender From United Kingdom, joined Feb 2004, 244 posts, RR: 0
Reply 16, posted (1 year 3 months 1 week 1 day 15 hours ago) and read 3950 times:

A conventional amp meter needs to be installed in series in whatever circuit it is measuring the current flow.

An Amp-Clamp however is a device which can measure the current flowing in an electrical cable simply by clamping around the cable and doesn't need to be physically connected to the electrical circuit.

If an electrical hydraulic pump has a high internal leakage then it will have to work harder than normal to maintain normal system pressure, therefore drawing more amps than normal. Internal leakage is used to cool and lubricate hydraulic system component but with age and wear this leakage can become excessive and the component will need to be replaced.

In fact, if any component in a hydraulic system (except the EDP) has a high internal leakage the hydraulic pump will work harder than normal, so by isolating or operating components in the system you can determine the component with the excessive internal leak.

In fact, I think the only part of a hydraulic system an Amp-Clamp cannot measure the internal leakage of is the engine driven pump.


User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3708 posts, RR: 34
Reply 17, posted (1 year 3 months 1 week 1 day 4 hours ago) and read 3912 times:
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Ah.....I know what you are talking about now. I used that method on the DC-10 that had a multitude of hydraulic maintenance valves to isolate various parts of the hyd systems. That was not possible on the 747 Classic all you had were the wing & tail flight control isolation switches.

User currently offlineApprentice From United States of America, joined Jan 2013, 118 posts, RR: 0
Reply 18, posted (1 year 3 months 1 week 10 hours ago) and read 3826 times:

Quoting aerotech777 (Reply 11):

[QUOTE] I thought the AMM does not mention clearly the type of leak check specific for each fluid (fuel, oil, hydraulic, air): for example it does not say the dry motoring if good for hydraulic leak check, idle for oil leak check, or part power for fuel leak check,...etc. If it does, it will be nice if you can post an example from the AMM (Boeing, Airbus,...). [/UNQUOTE]

For both Boeing and Airbus, AMM from B767/A340 on, in the remove and replace section you may find clearly indicated which test should be performed after item installation is completed for both leak and operational check. Then, in AMM ATA 72 all test are described.

RGDS



A "NO" is a positive answer. My Tutor
User currently offlineaerotech777 From United States of America, joined Aug 2009, 69 posts, RR: 0
Reply 19, posted (1 year 3 months 5 days 14 hours ago) and read 3728 times:

Quoting Apprentice (Reply 18):
For both Boeing and Airbus, AMM from B767/A340 on, in the remove and replace section you may find clearly indicated which test should be performed after item installation is completed for both leak and operational check. Then, in AMM ATA 72 all test are described.

I am aware of this (at least in the AMM of certain Boeing aircraft). My question was not related to leak check after the removal and installation of engine components. My question was related to the type of leak check (dry motoring, idle, part power) when there is leak (not related to testing an engine component after replacing it) and you have to performe leak check to detect the origin of the leak to fix it. I think the AMM does not mention clearly the type of leak check for each hydraulic fluid (hydraulic, fuel, oil, air) : for example it does not state that the dry motoring is required for hydraulic system, idle check is required for oil system, or part power check is required for fuel system.


User currently onlineyeelep From United States of America, joined Apr 2011, 671 posts, RR: 0
Reply 20, posted (1 year 3 months 5 days 14 hours ago) and read 3721 times:

Quoting aerotech777 (Reply 19):

737NG AMM 71-71-00 engine vents and drains inspection.


User currently offlineaerotech777 From United States of America, joined Aug 2009, 69 posts, RR: 0
Reply 21, posted (1 year 3 months 3 days 16 hours ago) and read 3616 times:

Quoting yeelep (Reply 20):
737NG AMM 71-71-00 engine vents and drains inspection.

Thank you.

Regards.


User currently offlineHAWK21M From India, joined Jan 2001, 31712 posts, RR: 56
Reply 22, posted (1 year 2 months 3 weeks 3 days 4 hours ago) and read 3286 times:

Quoting vc-10 (Reply 15):

I've no idea what the 'Amp-Clamp' method i
Quoting Mender (Reply 16):
An Amp-Clamp however is a device which can measure the current flowing in an electrical cable simply by clamping around the cable and doesn't need to be physically connected to the electrical circuit.

Its a quick procedure and can be performed with minimum manpower.



Think of the brighter side!
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