lincoln
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"High Pressure Bleed Valve" Problem

Wed Dec 27, 2006 5:37 am

Before a recent 757-300 flight the captain walked over to me and told me that it was going to be a "bad day" because the inbound crew had reported having problems with a "high pressure bleed valve" in the #1 engine. He also told me that the aircraft was going to be towed to the hanger so they could replace it and the delay would be about an hour and a half.

Sure enough, about an hour and a half later we were boarded and the flight was uneventful.

To get to the point: I was just curious what the purpose of this valve was, and what if any symptoms would be exhibited?

Thanks -- and Happy Holidays

Lincoln
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SlamClick
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RE: "High Pressure Bleed Valve" Problem

Wed Dec 27, 2006 5:48 am

Jet engines take in more air than they need to run themselves. Some of this air is "bled off" at the compressor section. Some is bled off just to relieve overpressure and it is simply ported overboard - usually through the fan discharge cowl ducting.

But a lot of bleed air from jet engines gets used for pneumatic power (air pressure) such as wing, tail, or engine cowl anti-icing and the big one - air conditioning and pressurization.

The cabin is pressurized with conditioned bleed air. It is bled of the engines at "low" and "high" pressure stations, blended, cooled, conditioned, filtered and ducted into the cabin. From the cabin some recirculates back into the a/c system. Some might vent out of the cabin by way of radio racks and circuit breaker panels and electronic compartments, then through the baggage pits to warm and pressurize them, then overboard through a pressure-regulating "outflow" valve.

If we lose a high pressure bleed source we have lost a significant part of our bleed air and may have altitude restrictions or even be prohibited from flying in icing conditions.

Worse, if it failed OPEN we would have very hot, very high pressure air pouring into a system designed for lower temps and pressures.

At worst, full open HP bleed can burn through the ducting and damage nearby components.

Hour and a half? I'll bet at least half an hour of that was paperwork.
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Valcory
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RE: "High Pressure Bleed Valve" Problem

Wed Dec 27, 2006 8:10 am

Quoting Lincoln (Thread starter):
To get to the point: I was just curious what the purpose of this valve was, and what if any symptoms would be exhibited?

Bleed air from jet engines are usually tap off at the copressor at intermediate stage (usually 5th or 9th stage depends on the engine) and high stage (usually 14th stage). The high pressure bleed valve is usually refer to as HPSOV(High Stage Shut Off Valve).At idle bleed air comes from high stage at high power settings(around 80% N1) bleed air comes from the intermediate stage,it is more efficient that way.The HPSOV shuts off when the pressure is high.The HPSOV works in conjunction with the high stage pilot/controller(the brains usually tells hpsov when to close.Problems cause by the HPSOV failing are usually duct pressure problems(low Duct pressure, fluctuating duct pressure,not changing from high stage to intermediate stage,no engine bleed air etc) The PRSOV (High Stage Pressure Shut Off Valve/Engine Bleed Valve) is use to turn and off the engine bleed.If the duct pressure is too high or too hot the PRSOV will close and no engine bleed air will be available from that engine.To check if the high stage system is working we usually do a bleed shift (basicly changing from high stage to Intermediate stage). When the engine is running you advance the trottle(increase power) the duct pressure will increase then decrease then increase again (Usually happens around 80%N1 basicly you are changing from high stage bleed to intermediate stage).I hope this helps
 
NKP S2
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RE: "High Pressure Bleed Valve" Problem

Wed Dec 27, 2006 8:12 am

Quoting Lincoln (Thread starter):
To get to the point: I was just curious what the purpose of this valve was, and what if any symptoms would be exhibited?

Poor air conditioning/heating at low power settings, or possible difficulty maintaining cabin pressure at low power settings. Poor wing ainti-ice performance...Or...High bleed air temp and pressure at higher power settings causing the bleed air volume to be regulated lower, if not an outright bleed trip for that associated engine.


To replace an HP valve wouldn't require the A/C to be inside a hangar, so my somewhat educated guess is it was brought to the general hangar hardstand so as to prevent a gate space issue and allow a place run to ops check it. Many times it might not be the valve itself as the problem but may be a pneumatic sense problem caused by a leaking line or connection, or even an electrical issue. Seems that in most cases it takes longer to troubleshoot and figure out what's wrong than to actually replace/repair the offending item.

[Edited 2006-12-27 00:17:54]
 
kaddyuk
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RE: "High Pressure Bleed Valve" Problem

Wed Dec 27, 2006 8:24 am

I'll Add to whats already been said...

Quoting SlamClick (Reply 1):
it is simply ported overboard - usually through the fan discharge cowl ducting.

Most modern engines bleed into the LP Fan Stream instead of Overboard (like older engines). This is to maintain Mass Air Flow.

Quoting Lincoln (Thread starter):
He also told me that the aircraft was going to be towed to the hanger so they could replace it

There would be no need to tow to a Hangar for this job, i've changed at least two in the last 6 months and the task as mentioned only takes 50 minutes start to finish including an idle bleed check.

Quoting NKP S2 (Reply 3):
Many times it might not be the valve itself as the problem but may be a pneumatic sense problem caused by a leaking line or connection, or even an electrical issue

On the trent 500 at 'A' Check there is a card to DVI the IPSOV. Its a real swine as the SOV is really "pinched" in place by the offtake elbows and there is a real knack to getting it in and out first time.

Quoting SlamClick (Reply 1):
Hour and a half? I'll bet at least half an hour of that was paperwork

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lincoln
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RE: "High Pressure Bleed Valve" Problem

Wed Dec 27, 2006 9:15 am

Wow! Thanks for the quick and thorough replies, shows that there's a lot to be learned from this fourm.

Quoting NKP S2 (Reply 3):
To replace an HP valve wouldn't require the A/C to be inside a hangar, so my somewhat educated guess is it was brought to the general hangar hardstand so as to prevent a gate space issue and allow a place run to ops check it.

This was gate 60 at LAX; no other flights used the gate while we were waiting but the clearence at that gate (to a lay person, at least) appears to be a little tight and the gate agent did make an announcement to the effect of "they're finished replacing the part and the paperwork, they're just going to do a run-up check on the engine before towing the aircraft back to the gate" right around the 1 hour mark.

I'm not sure where at the airport CO does their MX work, but my personal thought was towing the aircraft away from the gate and then back probably took as long as the actual repair.

Lincoln
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liedetectors
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RE: "High Pressure Bleed Valve" Problem

Wed Dec 27, 2006 12:02 pm

Quoting SlamClick (Reply 1):
and the big one - air conditioning and pressurization

SlamClick you are 99% correct in your decription of the bleed air system. The largest demand for bleed air is the wing anti-ice system rather then the ECS system. it gets real exciting on smaller airliners during idle decent, the debit for wing anti-ice is huge in relation to the overall airflow that it is hard to have enought thrust to maintain a reasonable rate of decent.

the contribution due to wing anti-ice will be a driver in determining the flight idle rating for the engine.
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Tod
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RE: "High Pressure Bleed Valve" Problem

Thu Dec 28, 2006 1:04 am

Quoting SlamClick (Reply 1):
But a lot of bleed air from jet engines gets used for pneumatic power (air pressure) such as wing, tail, or engine cowl anti-icing and the big one - air conditioning and pressurization.

Also a couple of small uses such as pressurizing the potable water system and on 747F straight bleed air is dumped into the fwd lower lobe to supplement the heating normally provided by the e/e bay exhaust on pax 747.

Tod
 
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HAWK21M
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RE: "High Pressure Bleed Valve" Problem

Thu Dec 28, 2006 3:48 am

The HPSOV should be line replaceable.What type Engine was this.
The RB211-535 has a High stage pilot controlling the High stage Shut off valve.This normally opens at lower RPM when the lower stage bleed is inadequate at lower EPR.As the Bleed Increases the HPSOV closes.

Quoting SlamClick (Reply 1):
I'll bet at least half an hour of that was paperwork.

Shouldn't paperwork be 50% of the time  Smile

regds
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avioniker
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RE: "High Pressure Bleed Valve" Problem

Thu Dec 28, 2006 10:05 am

I always thought the rule was that the paperwork must equal the weight of the part(s) replaced. . .
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Airgypsy
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RE: "High Pressure Bleed Valve" Problem

Thu Dec 28, 2006 10:12 am

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HAWK21M
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RE: "High Pressure Bleed Valve" Problem

Thu Dec 28, 2006 10:11 pm

Quoting Avioniker (Reply 9):
I always thought the rule was that the paperwork must equal the weight of the part(s) replaced. .

Then a QECA Installation would take a long time  Smile
regds
MEL
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remcor
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RE: "High Pressure Bleed Valve" Problem

Fri Dec 29, 2006 4:26 pm

I'm waiting for a post title someday to say something like:

"High Pressure Bleed Valve" problem - need help quick, plane takes off in 1 hour!


 Smile  Smile  Smile
 
xv408
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RE: "High Pressure Bleed Valve" Problem

Sat Jan 13, 2007 12:39 am

Flight International's Straight and Level section once reported an advert "Wanted urgently - fire extinguisher"!
 
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jetmech
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RE: "High Pressure Bleed Valve" Problem

Sat Jan 13, 2007 9:45 am

G'day Techies  Smile,

I thought I may as well add my 2 cents worth. I am a bit confused as to whether the original post was referring to a bleed valve in the pneumatic supply system or a bleed valve in the engine compressor casing. I am assuming it is the HP valve in the pneumatic supply system, and with respect to this, I found an interesting photo in the database.


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Photo © Pier Picone



This photo is of the Rolls Royce Trent 700 (RR T700) bleed system. The heart of the system is the big "Y" shaped ducting arrangement. There are three main valves in this arrangement, these valves being situated on each of the three branches from the central "Y" shaped ducting piece.

The motorised valve on the top left branch of the central "Y" piece is the bleed valve. This opens and shuts off the bleed air supply (and regulates pressure?) from the engine to the aircrafts pneumatic system.

The motorised valve on the top right hand branch of the central "Y" piece is the High Pressure Bleed Valve (HPBV). This valve opens and shuts to admit and shut off HP bleed air respectively. On the RR T700, HP bleed air is taken from the 14th stage of compression (not including the fan), which is also the 6th and last stage of the HP compressor.

Located on the bottom branch of the central "Y" piece is a non motorised valve known as the Intermediate Pressure Check Valve (IPCV). The IPCV controls the admission and shutting off of IP bleed air in response to movements of the motorised HP bleed valve. IP bleed air is taken from the 8th stage of compression (not including the fan) which is also the 8th and last stage of the IP compressor.

During low engine power conditions, HP air will be bled from the engine so that sufficient pressure exists in the pneumatic system. The motorised HPBV will be commanded to open. HP air will them come down to the central "Y" piece from the right hand upper duct. HP air now acts on the upper side of the IPCV, with IP air acting on the lower side of the IPCV.

Due to the pressure difference, the IPCV is forced to close. This simultaneously shuts off the IP bleed air supply, and prevents HP air entering the IP compressor. The HP air them passes through the upper left hand branch of the central "Y" piece, past the bleed valve and along the upper left hand duct to the aircrafts pneumatic system.

As the engine power increases, the pressure delivered by the HP bleed will increase. At a certain point, the pressure delivered by the IP system will be adequate for the pneumatic system, whilst the pressure from the HP system will become excessive. The HPBV is then commanded to close.

As the HPBV closes, the pressure on the upper side of the IPCV is reduced. Once below a certain value, IP compressor air can force the IPBV open and allow IP air into the lower branch of the central "Y" piece. IP air now flows past the bleed valve on the upper left hand branch of the central "Y" piece, and proceeds via the upper left hand duct to the aircrafts pneumatic system.

Beyond the upper left hand duct, the bleed air, whether HP or IP flows through a large pre-cooler before entering the supply ducts to the pneumatic system. The pre-cooler is an air to air heat exchanger. It uses fan discharge air to cool the bleed air before it is transported onto the aircrafts pneumatic system. I believe that the large open ended duct to the right and above the HPBV may be part of the fan air supply or discharge arrangement from the pre-cooler  Confused.

Anyway, does anyone know if the bleed valve also regulates bleed air pressure as well as providing shut-off function?

Regards, JetMech
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jetmech
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RE: "High Pressure Bleed Valve" Problem

Sat Jan 13, 2007 9:58 am

Quoting Kaddyuk (Reply 4):
On the trent 500 at 'A' Check there is a card to DVI the IPSOV. Its a real swine as the SOV is really "pinched" in place by the offtake elbows and there is a real knack to getting it in and out first time.

Sounds like a similar degree of difficulty to changing the IP check valve on a CF6! There was no doubt as to the quality and precision that went into the making of the ducts, as there was no way you could get the IP check valve out without removing several of the other ducts from the compressor casing.

The problem was, this precision alignment always seemed to disappear when you went to refit all the ducts. It was akin to wrestling a crocodile trying to get three or four seperate ducting elements close enough to be pursuaded into union by the duct clamps. You were also in big trouble if you dropped anything into the gaping holes left when you had the ducts off!

Regards, JetMech
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lincoln
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RE: "High Pressure Bleed Valve" Problem

Sat Jan 13, 2007 1:47 pm

Quoting JetMech (Reply 14):
I am a bit confused as to whether the original post was referring to a bleed valve in the pneumatic supply system or a bleed valve in the engine compressor casing.

Wow... Thanks for the explanation and that fantastic photo (I've always wondered what the insides looked like).

For the record, I -- the origial poster -- am uncertain as to which type of bleed valve I was referring to. All I know is that one of the pilots walked over to me and mentioned a problem with "the" "high pressure bleed valve" in one of the engines...Had I known there was more than one I might have asked, but all I could come up with at the time was "Uh...thanks. I guess it's best that that's taken care of before we leave the ground, right?" (This was about 15 minutes before the gate agents announced the delay, I felt so special  Smile )

Lincoln
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Tristarsteve
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RE: "High Pressure Bleed Valve" Problem

Sat Jan 13, 2007 6:54 pm

Quoting JetMech (Reply 14):
Anyway, does anyone know if the bleed valve also regulates bleed air pressure as well as providing shut-off function?

Sorry dont know about Airbus, but on the B777 the HPSOV controls pressure.
On B777 there is an HPSOV and a PRSOV which are the same pt nbr. They are pure mechanical and are controlled by seperate controllers, one of which also controls the FAMV. These controllers are signalled electrically and modulate a reference pressure line which sends muscle air to the valves to open them (spring loaded shut). In normal operation it controls the HPSOV to 40psi and the PRSOV to 50psi.
It is more complicated than that, press depends on altitude and antice etc.

I used to spend a lot of time flying as pax in Tristars. The old RB211 HPSOV was an open and shut valve. At TOD as the crew pulled the throttles back there was a distinct whoosh in the cabin as each HPSOV opened. It always woke me up. About 30 mins to landing, time to go to the loo and have my last beer!

Cheers Steve
 
Tristarsteve
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RE: "High Pressure Bleed Valve" Problem

Sat Jan 13, 2007 6:59 pm

Quoting Lincoln (Reply 16):
For the record, I -- the origial poster -- am uncertain as to which type of bleed valve I was referring to. All I know is that one of the pilots walked over to me and mentioned a problem with "the" "high pressure bleed valve"

It is 99 per cent certain he meant the HP bleed valve that supplies Pneumatics to the aircraft. He can see this on his EICAS/ECAM screen, and can see the low or high bleed air pressure.
The HP bleed valves that bleed compressor air to control surge are not usually indicated to the crew, and it is very unlikely that a pilot would know that there was a problem with them. He would have a surge, or difficult to start, not an HP surge bleed valve problem.
 
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jetmech
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RE: "High Pressure Bleed Valve" Problem

Sat Jan 13, 2007 11:55 pm

Quoting Lincoln (Reply 16):

No worries Lincoln! Perhaps HAWK21M would have more details on the 757 bleed air arrangement?

Quoting TristarSteve (Reply 17):
B777 the HPSOV controls pressure. On B777 there is an HPSOV and a PRSOV which are the same pt nbr.In normal operation it controls the HPSOV to 40psi and the PRSOV to 50psi.

G'day TristarSteve, thanks for all the info  Smile  bigthumbsup ! I'm guessing that the HPSOV is a High Pressure Shut Off Valve and the PRSOV is a Pressure Regulating Shut Off Valve? So if I understand correctly, both of these valves regulate pressure? Does this mean that the engine bleed system regulates to 40psi when HP air is used, and 50psi when IP air is used?

Quoting TristarSteve (Reply 17):
At TOD as the crew pulled the throttles back there was a distinct whoosh in the cabin as each HPSOV opened.

I remember being on a 747 after TOD and hearing a mild pneumatic whooshing sound that seemed to occur every 4 or 5 seconds. I have never figured out what it was!

Quoting TristarSteve (Reply 18):
The HP bleed valves that bleed compressor air to control surge are not usually indicated to the crew

Fair enough, I had this exact thought in the back of my mind but I was not too sure if there was any direct indication of compressor bleed valve failure. I will try to have a look at the MM tonight to see how exactly the bleed air pressure is regulated on the T700.

Regards, JetMech
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Tristarsteve
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RE: "High Pressure Bleed Valve" Problem

Sun Jan 14, 2007 1:06 am

Quoting JetMech (Reply 19):
No worries Lincoln! Perhaps HAWK21M would have more details on the 757 bleed air arrangement

The B757 having a RB211 engine works in a very similar fashion, except it is mostly pneumatically controlled.
It has a high pressure bleed from HP6 which is controlled by the HPSOV , sometimes called the Hi stage valve, and a IP bleed which actually comes from HP2, but RR confuse the matter by calling it an IP bleed.
The HPSOV opens when downstream pressure is too low and controls pressure to about 55psi. Downstrean the PRSOV controls pressure to 40-53psi before it enters the pneumatic system.
 
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HAWK21M
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RE: "High Pressure Bleed Valve" Problem

Sun Jan 14, 2007 5:38 pm

Quoting TristarSteve (Reply 20):

The HPSOV is controlled by the High stage Pilot.
The IP bleed air will singnal closure of the HPSOV thru signal by the HSP via HPSOV controller.As lP air flow increaes.

regds
MEL
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Tristarsteve
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RE: "High Pressure Bleed Valve" Problem

Sun Jan 14, 2007 8:02 pm

Quoting HAWK21M (Reply 21):
The IP bleed air will singnal closure of the HPSOV thru signal by the HSP via HPSOV controller.As lP air flow increaes.

Not quite. The system does not measure the IP bleed pressure. As the HP6 bleed pressure increases to a fixed point which is measured in the HSP the HSP commands the HPSOV closed. This fixed point varies with altitude. The IP air then takes over as the HPSOV closes.
 
steinberger45
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RE: "High Pressure Bleed Valve" Problem

Mon Feb 18, 2013 4:59 am

I've worked in commercial aviation for years. Are you talking about the High pressure valve usually called the High stage valve?. On a turn at a gate we usually lock the valve out and place it on Mel. I have never yet replaced one on a turn it requires waiting for parts and a power run. It may be replaced at a carrier hub but usually not out in the field.
 
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HAWK21M
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RE: "High Pressure Bleed Valve" Problem

Mon Feb 18, 2013 8:38 am

Quoting steinberger45 (Reply 23):
On a turn at a gate we usually lock the valve out and place it on Mel.

HPSOV is a defferable item under MEL.
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Goldenshield
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RE: "High Pressure Bleed Valve" Problem

Mon Feb 18, 2013 10:26 am

On the CF-34-3x, the high and low bleeds serve different, seperate systems, and cannot be open at the same time, which presents interesting operational issues, such as, if you have to run anti-ice, you also have to run the APU to maintain pressurization.

Thankfully, with the CF-34-8x, they designed it to be more in-line with other engines, such as the ones mentioned above, and making the reservers hydraulic.
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