Not a question... just a massive thank you for what you do. I'm just a regular guy with a passing interest, and wanted to know how a jet engine works. I've now watched loads of your videos and I find them absolutely fascinating. Even though I'm a novice, I think that you explain the very technical terms as clearly, concisely and as understandable as possible. Thank you sir!

This is the best explanation anywhere. Thanks! I teach at FSI and I have guided many low time pilots to this video.

Ive always had the understanding that "bleed air" had 3 types (as you said). Starting purge, running balance/cooling (the air sent to the center bearing is also needed for air flow stability along with cooling), and service air (used for running services outside the engine.

Bleed air valves are for air start purposes. Bleed air from the 13 stage or whatever the manufacturer deems is for deciding and air conditioning packs. On the Lockheed C 130 I worked on, you start #1 engine then open bleed air valve so the manifold is filled with bleed air to start #2,3,4 engines. Great video! (You must start the APU to utilize it's bleed air to start #1!)

this guy and his videos are awesome. the bleed valves are like a compression release in older, bigger motorcycle engines that you couldn't kick over unless you released some combustion pressure

We used bleed air on our ships for a lot of various things. Masker air was used to make the ship sound like a rainstorm to submarines. Prairie air to come out of the leading edge of the prop to change the signature of the ship. Anti-icing air for our intakes when it gets below icing conditions. We could also do cross bleed starts to start other turbines.

You Sir, are a super stud jet turbine bleed air expert. Thank you for a bit of your knowledge!

Thank you so much for doing these videos and answering questions. I am learning so many things about jet engines that have been on my mind for a number of years. I Have always been interested in this subject but being a big dummy do not know the correct question to ask or things get real complicated real fast and other commentators seem to be all over the place. You have a wonderful, natural gift. Teaching seems to be in your genes. It is also very obvious how much joy you feel when the word turbine is mentioned. You absolutely love your job.

In my previous experience bleed valves were called "blow off valves" in industrial centrifugal compressors. Those would be open until the compressor reached operating rpm and would slowly close after the VIGV reached maximum opening perecentage. Then the VIGV would close slowly and modulate as per requirement. That was done to prevent the compressor to go from idle to load all of a sudden which can cause surging.

thank you for the information regarding the bleed air. I'm working as a process control tech, one day we had a problem in one of the power generators. They were GE gas turbines with GE redundant control system mark VI. Operations couldn't start the generator because of a problem in the bleeding valves, there were only two bleed valves. After tracing back inside the turbine compartment, we have noticed that the bleed valve actuators are operated by the turbine's compressor output and this compressed air was controlled by a solenoid valve located in the accessory compartment where you will find the lube oil system ad the started motor with. After testing the solenoid alone by forced signal through the control system, we have found it functional and healthy. We asked the operation to try the generator for another start " cool down between every start was set at 30 minutes". Again another failure in the bleed valves. At the end we had managed to test the valves actuators alone together at the same time by using an external source of air supply and found a big deviation in time, about a 22 seconds difference. It was confirmed that this wasn't normal, and the main issue was in the second valve actuator leakage. It has been replaced and the deviation was set to be less than 3 seconds after the second startup of the gas turbine. The limit switches on every valve actuator was the main reference to us, because it was unsafe to start the turbine while the doors of the compartment were open. My questions: Are aircraft engines equipped with the same setup? Is this a real issue in aircraft engines? Are the bleed valves in the aircraft engines designed to also be used as a surge protection when startup? sorry for the long story, thank you again for your explanation.

I could listen to you all day long...

My school uses your videos all the time! Your going to be the reason I pass my powerplants classes haha

Funny you should know I grew up in rural Manitoba... my first jobs were all farm related. When I was a teen we flew Cessnas and Cubs like motorcycles and snowmobiles. Later working with the turbine crop dusters they always had trouble with bleed valves and shut downs. I've never flown an actual jet but the few times I flew those planes I was told if you can't land it you'll die and if you hurt it, the owner will kill you instead.

Thank you very much for explaining different types of bleed air and what they are for. also for addressing the load.

I want to thank you for this and all your videos, this is good infromation about the air bleed valves. When the engines starts, it makes easier to turn the engine and other reason is to cool down other componets of the engine. There is on point, the turbo prop entgine, this one doesn;'t use the power turbine. Thanks a lot. Please send some snow to here.

On the R.R. Alison turbine engines Ive worked on, for helicopters, the bleed air port has 2 functions. When the engine is at 60% or idle, air blows out of it back into the atmosphere so that the compressor doesn't blow the flame out in the combustion chamber. at 100% the airflow reverses to help feed the compressor and keep the engine cool. It all happens with no moving parts, its just part of the design of the compressor fan (13:1) in this case.

Great video. You opened up a can of worms with this subject. There are so many different uses for bleed/discharge air. You have everything you talked about plus more depending on the engine. There is labyrinth seal pressurization, engine anti-icing, aircraft inlet anti-icing, fuel system purge, emergency oil pressurization, balance piston seal pressurization and much more.

Sir thank you so much for your good works I am learning alot

Cool, I was about to ask what exactly it was. When he said that it was a single-spool turboshaft engine I figured it had to be a mechanical load. Neat idea to use what you already have and where you have a good idea about its power consumption. But sucking/blowing air through these sharp-edged variable holes is certainly going to make a huge noise. I was aware of all the different kinds of "bleed air", but never thought about the possible confusion. Another major use for "customer bleed air" is wing de-ice/anti-ice in most jet airliners.

Hi Jay, Thanks for the full explanation of 'bleed air'; it seem all kinds of systems like to suck air off of the compressor! Please note that I placed 'air' in between 'suck' and 'off'!! That homemade load machine is interesting & sounds like it would work to me, however most likely very noisy! I'll be watching for that video... Darren

Thank you 😊 boss🤝👍..simple but yet easy to visualise and understand.

I wish you lots of luck, since I would very much like to see that thing run :)

Jay, several military helicopters use turbine engines that use a bleed air system you may not be aware of. These engines include the T53 (all models), L-712 (to include the L-11 or L-7-11and all following models). There are many more gas turbine engines that we use in the military that use the same bleed air system. However, none of these same type systems use the air... for ANYTHING. These engines produce an excess amount of compressed air by the time it reaches the centrifugal compressor. So, to control over compression in the outer combustion chamber there is a system of bleed air that is comprised of a large vacuum operated bleed valve that in turn opens a bleed band that surrounds the case halfs usually just after the second last axial compressor stage. The band is a stainless steel band that when tightened it prevents bleed air. Whan the actuator is in open position the band allows a specific amount of air to escape right to the atmosphere as directed by several other system.... such as the fuel control, the torque sensor and for some a few other sensors. This bleed air system was the real first coined 'bleed air' because it is what it is, just bleed air, not 'service air'. But service air didn't sound right so any system using the name calls it bleed air. A truly well engineered turbine engine shouldn't need that kind of bleed air system... but it does. For ninety percent of all other engines... that's wasted service air. PS: Also, these same engines use a separate bleed air system that actually is used for service air. Most are just used for 'anti-icing' around the intake cowling. This air is of the highest pressure as it comes from what we call the 'hot air gallery'... and yes, after being squashed as it does in a turbine engine... it really does get hot. This gallery sits right over the blades of the centrifugal compressor. The point at which the air is at it's hottest. As we techs know... hot is bad, even for intake air. The hotter the intake air is... the less expansion it is capable of during combustion.

Good Afternoon Jay!! You Grew A Beard Mate! Keep Up The Good Work Brother!!!

One part you may or may not have mentioned on here what bleed air is used for besides a/c, cabin pressurization. It's is also used for de-ice on the leading edges of the wings, vertical & horizontal stabs, windscreen and engine inlets. Also engine starting either from an APU or ground start cart like you use to start your engines at the test cell and to help pressurize hydraulic systems. I work on KC-135's and seen the different ways bleed air is used. There are great videos on KZfaq that go over the bleed air systems of many different aircraft types like from 737 to a 747.

such nice clarification ! thanks from Brazil !

Nice... Wish I could change professions this late in the game.

Man your videos are awesome! It's sad you hadn't reached yet the 100k subscription mark.

The Heisenberg of engines.

Thank you sir Greetings to you from Algeria

thanks agent jay z for all your videos very cool to learn about jet engines

thank you so much for this amazing informations they help me a lot on my research

Another fabulous video! Thanks.

Another great video, thanks!

I am confused. My prof told us that bleed valves, or what he called them, bleed hatches are used to bleed off the excess air in order to avoid surge of the compressor. Though, maybe he was right partially, since the only showpieces we have in our uni are the vintage soviet engines, and their age vary from 40 to 60 years or even more, and the older the engine, the more unorthodox it's construction is.

Thank you sir for the video

What I would like to know is the history of the use of compressor bleed for customer pneumatic power. What was the first engine to be designed with a system specifically to tap air off the compressor for airframe pneumatic power? What was the first aircraft, military or civil to use compressor bleed for pneumatic power? I'd also like to know what the first aircraft was to use an air cycle machine or pack for environmental control.

Jay, at 3:53 you talk about cooling the sump. Is there also a rotary pump that draws the air and oil out of the sump? Also, tell your developer to build a heat sink and install it around the ad on compressor. Have the working engine draw air through the heat sink. (naturally the heat sink needs to be configured right.) When the pressure drops around the heat sink, heat will be forced into the air. You will yield more psi and the process will be much more efficient.

Thank You, I wish that when I was young I could have learned about the systems on a jet engine. Thank Geo

Holy balls, that thing is going to be putting out a lot of air. I love it! I assume the goal is to get the company more involved with rebuilding and testing those -501 engines?

I relly learn too mutch from ur vids Thankyou

I never thought about how the engineers would have had to make so many provisions for air...like the blanket of air that surrounds the flame to cool it... No wonder jet engines can handle such an enormous flame within!!! Prior...I just thought it could handle those temps magically...and i was correct to always question that in my mind... AWESOME!!! Not understanding something mechanical, and knowing that I don't, bothers me, seriously.

Thank you so much Sir

I am wondering why a compressor section would be used for the load, as opposed to something already fully developed like a water brake. Although I guess this "air brake" load is self-cooling and can take the shaft rpm directly without reduction. Makes me chuckle a bit, visit a wood shop and all the jigs and fixtures are made of wood, in the metal fab shop the same bits are made of metal, I guess in the turbine shop everything is made of turbines!

Cool. Happy Canada day from Newfoundland. Should get a mike to reduce the residence. Great video.

Thank you ! A very informative video!

Of the three types of "Bleed Air" discussed; which is responsible for Engine Surge and how does clearing a surge (throttling back) prevent an engine from destroying itself?

Amazing!

Thx for this once again! 3500 HP compressor? Hook this up to your engine-lift-thing :-) (Maybe open the roof first...) I would like to wish you a powerfull pre-christmas time! Can't wait for the next vid!

I saw your video while I was searching for an explanation about active clearance control(ACC) but the video was about bleed valve and bleed air .it would be helpful if u could explain about ACC in modern tubofan engine such as ge90/genx.

I know that you are somewhat sensitive about answering questions that have already been answered.....completely understandable. However I have been trying to find the answer to this question in your videos and I have not yet had any luck. So....I will ask: Is there a quantifiable limit as to how much bleed air an engine can divert away from the combusters without effecting the performance of the burning of the fuel? A large commercial jet obviously uses vast quantities of compressed air to run various systems....is there a practical limit as to how much can be used without effecting thrust characteristics? Thanks much!

Bleed air also used (most importantly) for wing deicing and inlet anti-icing.

I have been studying the dynamics of internal shockwaves ( Mach+). Do you know of any good material on this as it pertains to turbine engines? Can you explain any of it in layman's terms? Thanks JayZ for all the knowledge you share!

Awesome video. Could you explain about free turbine engine ?

I imagine that this single shaft engine is the reason the engines on older hercs are shut down with the props locked in fine pitch, so they will be easier to start, where as the newer ones (J model etc) shut down with them feathered. I imagine the J model must have received a different engine with a free turbine.

Regarding cabin bleed air (air passing from the compressor directly into the cabin) is it safe to assume that the smells of fuel inside the cabin, are from worn bearing seals, or from jet fuel that somehow flows in that direction? I travel a lot and some planes smell more that others. I love your efforts here and actually bought the gas turbine book that you showed us. Keep up the good work!!!

T-58 bleed air used to extend the air refuling probe.

I realize it been almost 5 years since this video was posted but Back in the late 60's when in the USAF I ran the P&W J52 P3 in combined systems test cell of the AGM28B Hound Dog Missile and it had a series of bleed Valves around the compressor case at about the No 5 or 6 compressor wheel. I remember I had to check them when activated from the control room during the engine check portion of the combined systems check. What was the function of these bleed valves on the J52 P3? Any Ideas?

I have a little CAE-140 engine from a MA-1 GPU and I see a compressor bleed air path for a couple more functions. One assists in the actuation of the butterfly valve for the main compressor bleed (from the start cart), and the other leads, via a filter, to the hydromechanical fuel control unit. But maybe these aren't considered 'bleed air' because there is very little actual flow of air?

Nice hat!

Jay you have gone over several bleed air, on different engines, but can you find or create a video that shows how the two different systems work (Bleed Band System, Bleed Valve System). I have scoured FAA.gov, 8083, and jeppessen books and the best i can find are some poor drawing diagrams that don't explain or show their functions well at all. thank you.

Excellent description of a complex subject. Those two side by side bleed valves...can I think of them as a sort of "Compression Release" for startup purposes ? They let air bleed out during startup, to allow things to get up to a self sustaining speed more easily, without so much resistance? The other types I understand from your description...

Regarding the bleed air uses, what kind of pressure(psi) and air movement(cfm) run through the bleed air systems?(as in the Orenda engine I figured that the different uses of it require different amounts of air and use "restrictions" in some fashion. Love the channel Jay!

Why the air bleed band can prevent engine surge?

depending on what craft is asking the question ...myself I would refer to it as a dummy load

Thans

The big disadvantage I see with the single shaft systems is the power needed for starting. You've mentioned the LM1500 and LM2500 are started with about 100hp, can you give an indication of how much hp this engine needs to start? I imagine it would be quite a bit higher than engines producing thrust or powering a free power turbine. It also looks like this load system wouldn't produce much load until the engine got to running RPM. I imagine that would make starting easier than normal, right?

is bleed air hot? is it because of compressing the air?

Also bleed air for leading edge flaps on F-4 Phantom

On the load for the allsion, I am assuming that closing the valves on that compressor increases the load since the air has now where to go.

another great video thank you for the effort just to educate us very selfless on your part and I appreciate it. question for you the bleed air you called customer bleed air for systems on plane is this the same one planes use to start other engines with or is that a different bleed air outlet? looks small for the size of hose starters use but I don't know. Thanks again Jay

The Orenda no-doubt has transpiration-cooled turbine blades. Correct?

There is also a bleed air exit (I guess from the 4th stage of the Compressor for this case) that is used for anti-icing of the inlet guide vanes, am I wrong?

Thanks so much!!

This technical man is like the chemical man ( in Breaking Bad ).

Nice hat Big ole pimp. The only real jett

hi sir.. thank u for ur nice efforts. I have a question about ,is there a difference between compressor bleed valve which is used to avoid compressor stall and surge and a bleed valve from which bleed air is usually taken for the purpose of de-iceing,cabin pressurisation,etc

Is the cooling air that cools the bearing also what pressurizes around the bearing inclosure to keep oil that gets past the seal out of the engine? what would the range of air pressure and what temps would you see when engine is at operating power? Is the air that is used by the plane systems closed circuit like when a car uses vacuum servos where there is no leak of pressure or vacuum in cars and just the pressure itself is doing the work? Thanks for the hard work you have a first rate site.

If this is one of those questions that's been answered a million times, just say so and I'll hunt for it on my own (or you can point me in the right direction). I'm just curious; as busy as you must be, what motivates you to take the time to make these videos?

Agent Jay z... I have a question but it's not about the bleed valves/ air. where do carbon deposits on the main oil filter come from specifically for PT6A-27?

is that a vibration analysis kit hooked up on the t56 turbine? also thanks for the great vids! being a jet engine troop i love watching these videos and seeing other engines!

Do you have a video where you explain how the different chaising parts are held toghether?

I noticed you said that the bleed valves open on the 501 because the high pressure section can't handle the air from the low pressure section on start. That makes sense but I guess I am confused because you later said the 501 was a single shaft engine. Why are the bleed valves needed on a single shaft engine lacking an HP system? Thanks!

Are there any questions that you wish someone would ask? Your answer is my question.

Great vid, once again, thanks (missing playing with donks). Now with regards the inlet appertures on your load compressor. What's the risk of inducing compressor stall on the load unit? It must surely induce majorly turbulent airflow onto the first stage, doesn't it? Have you done a video of the unit running? I'd love to see the results. Thanks, once again.

The air, coming out from that 'mecanical load' cmpressor, should have quite a high temperature, like 300+ celsius. This air will be sucked to the main engine intake as they are close. So, isnt it bad for the engine to be feeded by such a hot air?

Bleed valves seem so much simpler than variable stators for avoiding compressor stalls on engine start. My don't jet engines use bleed valves?

I have a question for you ? I am a AD in the Navy i work on the T-56A-14 or 501. Why is it that that you guys are taking the air on the old compressor section from the bleed valves on the 5th and 10th stages vs the 14 stage on the diffuser section, wouldn't you rather have 14 stage bleed air?

Amazing video! So that is basically the same concept as an engine dynamometer used to produce a variable and measurable load to test the performance? How is the output tq being measured by the driven compressor? Is this as simple as psi air to percent aperture will equal tq required to produce and how are these numbers determined or is there some type of load sensor directly attached to measure output? Thank you for the great videos!

What is the typical temperature and pressure of bleed air for customer utilities?

Jayz is the guy.

Thanks man !

why don't they call the bleed valves compression release? also, on the engine "dyno" don't you need a valve on the exhaust side of the compressor more than the inlet or is there enough restriction in the end plate that the bleed air system will do? i assume the intake restriction is for unloading the engine at startup. if you were to shut the intake valve quickly while the "dyno/load" was at high load, would it attempt to stall the compressor?

I have been trying to figure out how the shaft start rotating when the engine is at rest

so there is customer "bleed air" for aircraft usage, and then there is internal cooling air, that's the air ducted thru the engine thru pipelines and valves used to cool certain parts of the engine most specifically, the combustion section and the turbine section. But what about the external cooling you were talking about? like I know that it mixes with the gas path downstream of the exhaust, but what does it specifically do?

Great Videos and something i like to watch. I have one question i.e. you said the HBV assist in starting? I thought they are there to help in surge operation to release the pressure from compressor.

I've always wondered what compressor stall is, ive read descriptions but they are all a bit abstract so hard to get my head around. Especially when the air reverses flow and flames come out the front, i really don't get how that happens.

AJZ, Good video about bleed air. In an airliner does the cabin ventilation and pressure come from bleed air? If so, what is the proximate cost in loss of engine efficiency ? The reason I ask, in the early days of jet airliners there seemed to be never a lack of cool air in the cabin but now you get baked until you have reached 10,000 feet or so. I think cabin air is being recirculated to cut down on the use of bleed air off the engines to save fuel. Thanks for you time, John Valos

I think people also get it confused with RAM air and APU Bleed

I was wondering if you could explain how blow off valves (or BOVs) function? It is my understanding they are operated not just during startup and are activated somehow by a pitot tube measuring airflow velocity and are hydraulically opened/ closed. Is there some sort of control unit in between? Could you clear this up?