Re: 737 Pneumatics System Question

Date:         25 Mar 97 03:38:11 
From:         D Snow <>
References:   1
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On 20 Mar 1997, Jim Messina wrote:

> The 737-300 engine bleed valves are (according to an Aircraft Flight
> Manual):
> 1. Shutoff valves
> 2. Pressure regulator valves
> 3. Reverse flow check valves
> Are there versions of 737s that do not use the Reverse flow check valve
> feature?

>From what I can tell on my 737-200 Flight manual.  No.  The 8th stage
bleed valves are flow check valves as well.  The 13ths stage bleeds are
modulating and shutoff valves, which would probably be a "one-way" valve
as well.

> To extend the idea further, will you ever be able to heat up the engine
> cowl inlets with the Engine Anti-ice switches "on", while on the ground,
> with ONLY the APU running?

No.  The engine cowl is deiced by 13th stage bleed, controlled by the cowl
valve, and the Engine Inlet itself is deiced by the 8th stage, thru the
left and right valves.

The 737-300 engine is different.  Engine Cowl anti-ice on the 733 is
provided by the 9th stage bleed thru the modulating and shutoff valve.
Since according to my diagram here there are no one-way valves in the
engine plumbing, other than the 5th stage bleed valve, it looks like with
the engine bleed valve OPEN, and the Engine Anti-ice switch ON, on the
733, it looks like one would be able to use engine anti-ice with ONLY APU
bleed air. BTW, packs would have to be OFF.

Can we play more trivia? :)
Douglas Snow                       (Currently INOP)