B1900 environmental

[max6462]

Quick questions for clarification:
1- In case of total electrical failure, is the vessel still pressurized?
(Ouflow valves would open ?)
2- Must bleed valve (one at least) be opened for air cond. to fully
operate (cooling)? or EMC auto+ temp ctrl decrease fully and
bleed envir off is enough?

[GearDoor]

Hi, I had to dig out my 1900 Flight Safety manual to try and come up with the answer to this one.

The outflow valves are pneumatically operated by vacuum pressure from the pressurization controller, so an electrical failure shouldn't cause them to open. If the pressurization switch is placed to "DUMP", the outflow valve is opened via a dump solenoid. However, this probably wouldn't work during a complete electrical failure.

"If a complete electrical failure should occur, both environmental regulator/shutoff valves would fail to the closed position. No more bleed air would enter the pressure vessel and cabin pressure would leak down." (Flight Safety Manual, p.8-4)

However, if you still had battery power, you could still open the left bleed valve, since it has that white ring around it.

[mtnflyer]

Hi max
in the beech there's 3 elec systems- 2 generators and a battery.common scenario in the sim is a gen failure followed some time later by a fault on other side,say a fire.if you shut it done immediately you've created a dual gen failure!so now you've batt power-ie it's limited.
on the copilots subpanel the white circle around the bleed valve signifies that bleed will still have elec power,but not for terribly long as the batt will drain.say 30 mins approx.
so to answer you Q.yes the bleed will work,but for a limited time.
also note on the start sequence.see the redlight items.before start the "envir fail" annunciator will remain illuminated until one of the gens comes online.just another way of looking at it....

on the bleeds.-one bleed needed for air conditioning.the VCM is not unlike those wall unit airconditioners found in hotel rooms.it needs room air to work-takes it in the bottom and forced to cool and exhausted out the top.so to get any air into the cabin we need air(envir) thru the bleed valves and this air is then give to the a/c unit the VCM to get cooled further,if needed.
there are 3 ways to turn the vcm on, all using the mode controller.
1 turn the controller to man cool-easy
2 turn it to manual and bring the manual switch to its coolest position
3 turn it to auto and turn the auto knob all the way down and vcm will turn on if oat > 45f(might be 55,cannot remember)
hope this helps,mtnflyer

[max6462]

I found in my FSI books also the straight forward answer for the case of electrical failure.
As for the VCS i agree, makes sense. I wasn't certain of where the VCS would get the air from ( I was assuming vessel).
VCS is controlled by temp controller.
Can't find that answer in my books though.
Thanks quys, I'll dig more.

[Cardinal]

mtnflyer
on the bleeds.-one bleed needed for air conditioning.the VCM is not unlike those wall unit airconditioners found in hotel rooms.it needs room air to work-takes it in the bottom and forced to cool and exhausted out the top.so to get any air into the cabin we need air(envir) thru the bleed valves and this air is then give to the a/c unit the VCM to get cooled further,if needed.

I have to disagree with you here. The VCM will function all day long without any bleed air. The blowers simply recirculate cabin air past the VCM-cooled heat exchangers. Additionally, the ACM air (from the bleeds) is completely separate and running through a different circuit than VCM/Blower air. From the FlightSafety B19000 manual, page 9-5:

"Two evaporator blowers recirculate cooled cabin air. Evaporater coils are mounted on the inlet side of the evaporator blowers to facilitate the exchange of heat between cabin air and the cooling freon when the vapor cycle sytem is operating. The evaporator blowers recirculate cabin air through the eyeball outlets".

[Coastrider26]

Max,

The VCM will work without the bleed air open try it in summer you'll notice it. It's not warm enough at the moment to feel the difference.

And on some planes you don't even need a total elec fail to have the cabin "drifting" :E

[snowbirdbrad]

The way I look at it is this:

The environmental valve is powered open, so loss of power = valve will close,
The instrument valve is power closed, so loss of power = valve open.
Reason: I figure design was for safety, is power lost to the system, the safety is to ensure the boots will still inflate, pressure can be dealt with by descending but from a safety standpoint the boots need to be opeational.

Circle on the switches, another easy way to determine additional load shed in case of a dual gen failure. anything without the white ring, to my knowledge, will be load sheded, so when determining what else to shut down, just find the rings.

[Dockjock]

Further to this subject, can anyone confirm the capacity of the ACM v. VCM in terms of cooling?
According to our engineers, the ACM can cool to 15C below OAT, while VMC can cool to 20C below OAT. In other words VCM only provides additional 5C of cooling?

[Cardinal]

Close. The ACM will cool about 15C below ambient OAT, while the VCM will cool 10 below the ambinet CABIN temp, (remember its recirculated). FWIW, FlightSafety says that the ACM can chug out 64,000 BTUs. and the VCM 46,000.

[Dockjock]

By saying it can cool to 10C below cabin temp does that not create a so-called infinite feedback loop? ie. cabin is 20C, VCM can cool it to 10C, cabin drops to 19C, VCM can now cool to 9C and so on. I think there must exist a finite limitation in relation to OAT.

In any case its never enough when its hot out...and the 180-day MEL doesn't help either.