Pulling the fire handle?
 

Did a search , but didn't find anything that thoroughly answered my question. When pulling the fire handle, you isolate fuel, bleed air, hydraulic, electric. But where does the physical dis-connection actually occur? My understanding so far:

1. Electrical - GCB and GCR

2. Bleed air - Bleed air control valve

3. Fuel - Fuel spar valve. I thought I read somewhere that certain designs also pull a valve in the HMU. Would this be the same HP SOV as is controlled by the fuel lever in cockpit for normal start/stop?

4. Hydraulic - this one got me. In case of an Engine Driven Pump, would it be physical disconnection from the gearbox?

I don't fly anything bigger than a MEP!

Thanks in advance

Not all are the same but yes some/most will shut off at the SPAR and the HP SOV

Most Boeings just cut the supply off so the pump still has fluid in it but will require overhaul due to overheating.

hyd shutoff
 

Since the engine's shut down, you're probably not going to overheat the pump? Even windmilling with fluid in it, though that's a minor consideration in the overall scheme of things.

Some designs also silence the fire bell....automatically.
Keep in mind also that many of these electrically operated fire pull handles activate certain functions, powered directly from the (always) hot battery bus.
Many variations, depending on specific aircraft type.

Pilots should know what these functions are, for example...
Type L1011.
The pilot walks onto the flight deck, and finds no ground power connected, APU not operating, and the ships battery switch in the OFF position.
Then, he pulls the number one engine fire pull handle.
This action sends electrical power to close the number one engine tank valve, because the DC power comes from the (always hot) battery bus.
The question then is...can the pilot confirm that the respective tank valve has closed?
The answer is yes, because...the blue valve intransit light will illuminate briefly, as the valve closes.
Further, now that the engine fire handle is pulled, can both engine fire extinguishers be discharged?
The answer is yes, because, DC power is available from the hot battery bus.

Should have been a bit more specific, with the lack of supply fluid the case drain fluid cooling becomes less effective so the fluid will overheat and contaminate the the pump therefore requiring overhaul of the pump.

The Hydraulic supply valve closes.The pump is still engaged to the gearbox.

Cheers for your answers! :)

Hi, to answer your questions, I it really depends on what type, or category of A/C you're talking about. What I think you'll find those questions are really type specific, with a few generalizations.

I currently fly 3 turboprops (I know, way too much review required), and they are all different.

In the Saab pulling the T-handle will silence the warning, close the fuel shutoff valve, close the bleed valve, open the generator relay, arm the extinguisher squib, and reset the master warning system.

Where in the King Air, the "Firewall Fuel Valve" is just that, it only cuts off the fuel at the firewall (before the low pressure pump).

Normally the Pratt turboprop engines are shut down by cutting off the fuel after the Fuel Control Unit FCU (GE calls theirs an HMU), this is done by the condition lever, while the T-Handle blocks the fuel before the first pump.

Cheers,
ftp

edit: poor coherency at 1am

And still engine fire memo items require to cut fuel supply to the engine before discharging any bottle. I believe that's done just in case the whole fire pull sequence doesn't close said valve, like some sort of redundancy. Am I right?

So here's a question that no-one has ever given me a confident answer on... If you pull the fire handle in a 737 - can you reset everything by pushing the handle back in? I know you probably wouldn't want to... but just humour me.

Yes, resetting the fire handle returns all the systems to normal. Need to cycle the Generator control switch off and on to get that back but nothing else.
Same for Airbus - designed that way in case of accidentally pulling the wrong fire handle.

If you're interested, pulling the fire handle on a 146/RJ will shut off the LP cock although it'll take the donk about 2 minutes to flame out at ground idle!