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Engine Bleed Pressure


munirabbasi
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Hello  T56A -15  power plant Pneumatic  Expertise

T56A-15  (C-130 E model) engine can provide approximately 155 pounds of air flow per minute at 635F and 125 pounds per square inch of gauge pressure.  Bleed manifold pressure gauge is mounted in F/deck  (direct gauge) display approximately 70 PSIG .where  remaining  pressure of  the engine flow?

Best Regards

Munir Abbasi

Home of Hercules Pakistan

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at sea level, a 0/low time compressor will make 80 to 85psi at normal ground idle. This increases 

as throttle is advanced towards take off an TIT increases. The highest I have ever seen was 130psi.

This was a 0 time engine where the CDP fell in "high" zone of the compressor graph. Compressor

performance is based on OAT and pressure altitude.

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10 hours ago, pjvr99 said:

at sea level, a 0/low time compressor will make 80 to 85psi at normal ground idle. This increases 

as throttle is advanced towards take off an TIT increases. The highest I have ever seen was 130psi.

This was a 0 time engine where the CDP fell in "high" zone of the compressor graph. Compressor

performance is based on OAT and pressure altitude.

Thanks for excellent response .let me rephrase my query regarding Engine  bleed output pressure at Engines throttle higher setting. normally the pressure is indicated in flight deck bleed manifold Gage approximately 70 to 80 PSIG  where one engine output pressure is 125 PSIG at 155 ppm  . Question arise in my mind that one engine bleed output is metered 125psig but all four engines operating at higher throttles setting is droped to 70 to 80 psig when both  air -conditioning are ruing condition with flow rate  of 70 ppm and 30 ppm.

Best regards

Munir Abbasi

Home of Hercules Pakistan

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The Ejected pressure from the engine should never indicate exactly in the flight deck for quite a few reasons.

1.  Pressure drops across distance.  In order to get 125 psi in the flight deck, the engine would need to be making 150-ish psi at the engine (just an estimate).   Pressure drops across distance because flow and volume is required to get that pressure across a distance.  

2.  The system has allowable and normal leaks.  Every valve in the system is bleeding off or leaking a small amount.  Some are calibrated to leak a certain amount and others just leak as a result of their design.  Very few pneumatic systems are perfectly leak proof.  For example, if you have 20 valves in a system and they are all leaking small amounts of air, your 125 psi becomes more like 70 after the bleed offs.  This is why the system has a bleed down time.  The drop from 30 to 15 psi in 22 seconds or more is a indication a satisfactory level of "normal" leakage.  If there were no leaks in the system at all, your bleed air pressure would never drop.

3.  Almost all systems are like this.  Hydraulics, fuel, electrical, oxygen, etc.  The system is designed to provide a higher amount than is required so that it can "bleed off" some for normal system losses and still provide a set amount.  

Hope that helps.

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7 hours ago, hehe said:

The Ejected pressure from the engine should never indicate exactly in the flight deck for quite a few reasons.

1.  Pressure drops across distance.  In order to get 125 psi in the flight deck, the engine would need to be making 150-ish psi at the engine (just an estimate).   Pressure drops across distance because flow and volume is required to get that pressure across a distance.  

2.  The system has allowable and normal leaks.  Every valve in the system is bleeding off or leaking a small amount.  Some are calibrated to leak a certain amount and others just leak as a result of their design.  Very few pneumatic systems are perfectly leak proof.  For example, if you have 20 valves in a system and they are all leaking small amounts of air, your 125 psi becomes more like 70 after the bleed offs.  This is why the system has a bleed down time.  The drop from 30 to 15 psi in 22 seconds or more is a indication a satisfactory level of "normal" leakage.  If there were no leaks in the system at all, your bleed air pressure would never drop.

3.  Almost all systems are like this.  Hydraulics, fuel, electrical, oxygen, etc.  The system is designed to provide a higher amount than is required so that it can "bleed off" some for normal system losses and still provide a set amount.  

Hope that helps.

Tanks

Munir Abbasi 

Home of Hercules Pakistan

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