Bleed Air Leak Detection Systems 1

[HotBleed]

Hi all. I am trying to collect design, performance information and operating/service history for bleed leak detection systems as used on hot bleed air ducting. There are several different methods and implementations of leak detection, including eutectic salts, thermistors, single and dual loop systems. I am particularily interested in newer methods of leakage conveyance such as annular flow to dump points and methods of sensing threshold values. This subject is heating up (pardon the pun) as new design airframes migrate to composites. Any feedback on this subject would be appreciated.

 

[thruthefence]

I've seen aircraft that run plastic tubing along the bleed air lines, pressurized from the low pressure pneumatic system. A normally closed "Hobbs" switch references pressure in the plastic line, & when a bleed air leak melts the plastic, the pressure drops in the plastic line, allowing the "Hobbs" switch to close, triggering the annunciator. Not very elegant, huh?

 

[plasgears]

I have heard stories of B-52 crew having to climb across wheel wells and bomb bays with leaking bleed tubes nearby. Very hot and noisy. Temp pickups and hi freq microphones would appear the way to detect, but there are other sources of noise and hi temp. Good luck.

 

[WKTaylor]

Ref SAE ARP699E "High Temperature Pneumatic Duct Systems for Aircraft" and go-to Section 6. "FIELD MAINTENANCE AND INSPECTION CRITERIA" pg 98.

Regards, Wil Taylor

 

[jim787]

You really might want to consider an optical method. Most of these leaks take place at the V-band clamp joints, the reason being that mechanics over tighten the band clamps and the working high temperature environment cause the v-band clamp to take a set or stretch if you will. When these clamps stretch they by necessity have a larger internal diameter such that it now becomes almost impossible to get the proper sealing pressure on the joint flanges. Understand that an airline will use the “enough pressure to blow your hand out of the way” measurement technique to determine if a joint is leaking too much (on a metal plane), note that I said “too much” because a certain amount of leakage is tolerated. Any leakage that impinges on composite panels will definitely be a problem.

 

[bleedguru]

Single & dual loop eutectics are most common in commercial and some military airraft. There is a design for single point collection..Works for any size and any length of duct. Duct must be insulated, if it is hot it should be insulated. Works with any ambient or environemtal conditions. Search USPTO and contact owner.

 

[DavidLeyman]

I am, by nature, a propulsion specialist but persons such as I look at fire protection and detection devices so this is appropriate.
Firstly: B52? Plasgear - you should crawl down the leading edge of a Beverly to change the generator in flight or top up the oils. Damn great Centaurus sleeve valve next to you will give your ears a buzz for days - not to mention the view of the desert from 15,000'!
Jim 787: Excellent. I should have gone with optical pyrometry as, potentially the way to go. Not sure about the 'enough to blow you hand away' this smacks of the 'pink knuckle' method of torqueing up. 'V' band clamps should be torqued, loosened and re-torqued in accordance with basic engineering training and the AMM.
You might also consider 'Systron-Donner' helium tube with a metallic hydride element. I mention the company name (not mine, of course) because they were the first on the scene with it. It would suit leading edge anti-icing systems because it is extremely resistant to vibration.
Plastic tubes? Ye Gods - nice try.
Bleedguru has it right. Very common, simple and cheap + reliable. This is good until the optics are cheap and reliable enough.