DUCT PRESSURE SPLIT

This is a public forum for 737 maintenance related questions, requests and experience exchange discussions for every Boeing 737.


DUCT PRESSURE SPLIT

Postby hanish737 » 30 Apr 2008, 16:47

DEAR SIR

I AM A BOIENG 737-800 MECHANIC.KINDLY GO THRU THE SNAG/RECTIFICATIONS WE HAVE DONE SO FAR ON ONE OF OUR AIRCRAFT.THE PROBLEM IS DUCT PRESSURE SPLIT IN BOTH CLIMB AND CRUISE.BUT AFTER SOME RECTIFICATIONS THE SNAG AGAIN PERSISTS ,BUT NOW IN CRUISE.SO KINDLY GIVE UR OPINION/SUGGESTIONS ON THIS RECURING SNAG.I PERSONNALY SUSPECT 450 THERMOSTAT NOW AS WE HAVE ALREADY REPLACED PRSOV AND 390 SENSOR .
SNAG REPORTED/RECTIFICATION
*DURING CLIMB LEFT BLEED PRESSURE-15PSI AND RIGHT-45PSI DURING CRUISE LH-20 AND RH-45./ HIGH STAGE V/V, PRSOV, PRE-COOLER CNTRL V/V MANUALLY OPERATED SENSE LINE CHECKD FOR LEAKS.

*OBSERVED DUCT PRESSURE DIFFERENCE, CLIMB LH-15 PSI AND RH-45 PSI.
AT FLT LEVEL 390 LH-12 AND RH-38./ 390 SENSOR CHANGED
* DUCT PRESSURE DIFFERENCE DURING CLIMB AND CRUISE/HIGH STAGE REGULATOR REPLACD.GROUND RUN UP CARRIED OUT .LH duct pr-20 PSI.
*DUCT PRESSURE SHOWING SPLIT OF 25-35 IN FLT/GROUND RUN AT IDLE ,PRESSURE OK
*DURING CLIMB OUT OF FLT LEVEL 280 DUCT PRESSURE LH-18 AND RH-44.AT CRUISE FLT LEVEL 400 LH-25 AND RH-36/PRSOV REPLACED.GROUND RUN DONE.PRESSURE OK



*F/L 370 Pack split L 25 ,R 40 N1 96% /Carried out high pressure run up of Engines and found LH P duct pr.normal .N1 Vs duct press. Graph is attached , also carried out fault isolation procedures 36-10 Task 804 Para F 1 to 18 and found PRSOV high stage valve and Pre Cooler controller valve OK. No leak found in the sense lines.

Today it is reported that the LH pr was 20 psi and RH 45 psi in Cruise.



EXPECTING YOUR VALUABLE SUGGESTION


THANKS AND REGARDS

ANTONY A ARTHUR :)
hanish737
 
Posts: 2
Joined: 15 Apr 2008, 15:07

Re: DUCT PRESSURE SPLIT

Postby sr79 » 30 Apr 2008, 18:33

hanish 737 u definately have a temperature problem i strongly suspect the precooler control valve since the 390 has been replaced,sometimes u can wrench these vavles and they would feel good but u have to check the control pressure coming out of them,check the control pressure coming out of the precooler valve it has its own regulater built into the the valve lets us know your fix.
sr79
 
Posts: 26
Joined: 27 Mar 2007, 19:21

Re: DUCT PRESSURE SPLIT

Postby savmycntry » 01 May 2008, 14:38

I agree with sr79. Also take a good look at the pre-cooler control valve ‘kiss seal’, it’s mounted between the pre-cooler control valve and pre-cooler. If it is torn or the mount bolts have worked loose it can leak that precious cooling fan air.
Good luck.
savmycntry
 
Posts: 8
Joined: 01 May 2008, 10:56

Re: DUCT PRESSURE SPLIT

Postby sjap » 01 May 2008, 17:58

Or maybe the high stage valve may be leaking internally. Very often we find this valve "closed" and operates when tested, but internally it still leaks hot air, since the valve spring seal may be damaged or even loose from the butterfly ring. The hot air makes the prsov go to more close dropping the pressure.
An easy check is to manually open the psrov and supply APU bleed on the duct. Open the clamp of the high stage valve at the downstream side (9th stage side), if air comes out the valve leaks. It should be closed. You can also hear it leaking when listening in the outlet of the engine.
sjap
 
Posts: 707
Joined: 26 Jan 2007, 20:57
Location: Netherlands

Re: DUCT PRESSURE SPLIT

Postby sr79 » 01 May 2008, 18:11

sjap u maybe right but if thats the case if the high stage is leaking on takeoff u might get a bleed trip due to an over pressure condition im not saying your wrong by all means u make alot of sense
sr79
 
Posts: 26
Joined: 27 Mar 2007, 19:21

Re: DUCT PRESSURE SPLIT

Postby rambo » 02 May 2008, 07:49

Other possibilities could be Bleed Air Regulator , or Pre Coler Control Vlv failed in closed pos(butterfly drived broken).
---rgds rambo
rambo
 
Posts: 24
Joined: 27 Jan 2007, 13:54

Re: DUCT PRESSURE SPLIT

Postby welshman-abroad » 02 May 2008, 08:42

Have you checked all the sense lines for leaks? When we have bleed problems, its the first thing we do. I think it would account for aprox 80% of our bleed problems. Hope this helps.
welshman-abroad
 
Posts: 12
Joined: 26 Feb 2008, 22:43

Re: DUCT PRESSURE SPLIT

Postby sr79 » 14 May 2008, 16:46

hanish737 is the duct pressure split snag fixed please leave feedback thanks im just curious
sr79
 
Posts: 26
Joined: 27 Mar 2007, 19:21

Re: DUCT PRESSURE SPLIT

Postby hanish737 » 15 May 2008, 08:46

hai frnds

the snag is still under observation as the min duct pressure is 20 we r despatching it as its with in limit ,but now the a latest trend is the duct pressure at times are as follows
LH-20-25
RH-60 :shock: still bleed trip of has not come.... :mrgreen:



we have done all possible recitifications as someone here advised about leak check of sense lines, it was the frst thing we had done when this snag ws observed..

anyway throw some light if somebody gets some glare :D ..


thanks and regards
hanish737
 
Posts: 2
Joined: 15 Apr 2008, 15:07

Re: DUCT PRESSURE SPLIT

Postby rambo » 15 May 2008, 13:01

Are you sure your Bleed pressure Indicator is working fine.

If yes, you need to carry out complete "Bleed Health Check" as per AMM.
Besides there are lot of bleed troubleshooting tips in this very site, as collected by Mr. Sjap
---rgds rambo
rambo
 
Posts: 24
Joined: 27 Jan 2007, 13:54

Re: DUCT PRESSURE SPLIT

Postby savmycntry » 15 May 2008, 14:21

hanish737 wrote:hai frnds

the snag is still under observation as the min duct pressure is 20 we r despatching it as its with in limit ,but now the a latest trend is the duct pressure at times are as follows
LH-20-25
RH-60 :shock: still bleed trip of has not come.... :mrgreen:



we have done all possible recitifications as someone here advised about leak check of sense lines, it was the frst thing we had done when this snag ws observed..

anyway throw some light if somebody gets some glare :D ..


thanks and regards


Hanish, as Rambo said you need to complete the health check. Remember the AMM has a seperate health check for the precooler control valve, start there. Be sure to connect the needle valve to simulate the 390 sensor to see if the precooler control valve is performing correctly, (this checks the internal pilot press. regulators). Just follow the health check . If you do not have the tooling to do this check properly then change the precooler cntrl valve, I think due to the history this be be a good move.
Then press on with the BAR and PRSOV, Follow the health check. Pay particular attention to the 450deg sense line going up into the strut, spray it with leak detector pay attention to the sweged ends of the line, many fail here. Spray the housing of the BAR and it's B nuts, fix any leaks noted.
Move onto the high stage valve and reg. Do the same, perform health check and spray the reg, look for leaks.
Generaly if your P.C air is low you will then look for and find leaks with the leak detector.

When you do the repair confirmation you will need a high power run and need to keep at least 80% N1 for 5min to heat the sytem up and make sure the pressure does not degrade. Also did you check the kiss seal, no kidding it has caused this problem on our next gen's.

Good luck and update us please. :wink:
savmycntry
 
Posts: 8
Joined: 01 May 2008, 10:56

Re: DUCT PRESSURE SPLIT

Postby Marc » 16 May 2008, 10:05

Hi fooks,

Here some info from Myboeingfleet.

The min despatch bleed press is acc SL 737-36-013-13 18 psi inflight. Is about 30% N1 if you do a ground run.
For trouble shooting info See 737-MT-36-003 and 737-MT-36-004

If all bleed components are changed( prsov, high stage valve, BAR, hs reg, precooler control valve, 390F sensor, 450F sensor), don't forget to changed the precooler itself.
Because of engine vibration the bleed components go fubar, also the precooler will crack inside.

At our company we keep the engine vibration below 1.5 units to reduce bleed problems.

Good luck,

Marc
Marc
 
Posts: 8
Joined: 11 Feb 2007, 13:07
Location: NL

Re: DUCT PRESSURE SPLIT

Postby Monkey Wench » 06 Oct 2008, 12:33

Try intechanging the 450f sensor with the other engine and see if the problem passes over to the other side.
Monkey Wench
 
Posts: 3
Joined: 05 Oct 2008, 01:27

Re: DUCT PRESSURE SPLIT

Postby 737dude » 08 Jul 2012, 11:39

We have exactly the same problem as described here on one of our 737-800s. The LH duct pressure stays stable around 16-18psi during CLB/CRZ with the RH at around 38-40PSI. Its been written up many times in different ways, but so far the fault couldn´t be found.

Was anything discovered in your case Hanish? Did you manage to isolate it in the end?
737dude
 
Posts: 1
Joined: 08 Jul 2012, 11:31

Re: DUCT PRESSURE SPLIT

Postby IFixPlanes » 08 Jul 2012, 16:58

What parts did you check or changed already?
"...written up many times in different ways..." is not really the best way to tell us what trouble shooting is done so far. ;)
Without any details it could be anything.
Bobby is Hobby
IFixPlanes
 
Posts: 138
Joined: 09 Feb 2007, 12:07

Re: DUCT PRESSURE SPLIT

Postby sjap » 08 Jul 2012, 21:18

737dude wrote:We have exactly the same problem as described here on one of our 737-800s. The LH duct pressure stays stable around 16-18psi during CLB/CRZ with the RH at around 38-40PSI. Its been written up many times in different ways, but so far the fault couldn´t be found.

Was anything discovered in your case Hanish? Did you manage to isolate it in the end?


Do a health check on all parts, if nothing is found first replace the 390 thermostat of the PCV, since this one could not be tested on wing.
Very often this thermostat (390) fails. (stucked closed causing PCV not to open causing PRSOV moving to close causing low duct press)
sjap
 
Posts: 707
Joined: 26 Jan 2007, 20:57
Location: Netherlands

Re: DUCT PRESSURE SPLIT

Postby yeelep » 08 Jul 2012, 23:30

737 Dude,
You need to supply more information regarding what troubleshooting has been performed. Sjap is dead right, the health check of pccv and engine bleed air system needs to be performed in their entirety. Don't stop when one item has been found out of limits, many times it is multiple items that add up to the indicated problem.
Here is my opinion based on my own experiences, well over 50 separate events with over 97% success rate (I always follow up 1 month after to see if the problem repeated).
NG; when low duct pressure is the problem:
1. PCCV: Still the most common failure for me.
2. PRSOV: #2 on my probable failure list.
3. BAR: Pretty reliable.
3. Flex lines. Since the design has changed (larger diameter), hasn't been a real issue.
4. 390°sensor/450°thermostat. Despite what many others say, in my experience they have rarely failed(I've only changed one of each). Shotgunners favorite?
5. Pre-cooler; Never seen a bad one on a NG, on the classics they crack every once in a while.
6. HSV: About the same as the 390°/450°.

Sjap; what happened to the CFM bleed air troubleshooting guides you had on site? Were they dropped to avoid the same issues you had with Boeing. They are the best single source for troubleshooting this system that I have seen.
yeelep
 
Posts: 48
Joined: 21 Jan 2008, 12:25

Re: DUCT PRESSURE SPLIT

Postby sjap » 09 Jul 2012, 08:25

OMG! I had this file online on a seperate place to avoid data-overload on the sjap-site.
But that provider is old and deactivated. I forgot !
I placed the bleed guide on a new spot now:

http://www.sjapstore.com/737%20Bleed%20Air%20Test%20Guide.pdf

It is for the classic AND NG, just scroll down the pdf file for the NG section.

Another file was also dissapeared but now back online:

http://www.sjapstore.com/B-737-NG-WALKAROUND.pdf

Thanks for the notice yeelep!
And all Boeing-related-legal stuff is removed as far as Mr.Boeing pleased.

Regards
sjap
sjap
 
Posts: 707
Joined: 26 Jan 2007, 20:57
Location: Netherlands

Re: DUCT PRESSURE SPLIT

Postby 737ng » 05 Aug 2012, 02:26

Hy "hanish737" !!!

Did you chech the supply line for the BAR?
There is a small "U" tube and that goes into a T-fitting.
That welding very often breaks.

BRGDS
737NG
737ng
 
Posts: 33
Joined: 21 Mar 2011, 14:09

Re: DUCT PRESSURE SPLIT

Postby raghav » 05 Aug 2012, 03:27

Have u checked with precooler?

May be cracked or dirty
raghav
 
Posts: 66
Joined: 25 Mar 2012, 11:00


Return to - 737 technical questions & requests -

Who is online

Users browsing this forum: Majestic-12 [Bot] and 5 guests