The G450 oxygen system is unique among the GV types, in that the crew and passenger oxygen bottles are plumbed together and can be used by either. The only exception appears to be the therapeutic, which only uses the passenger bottle.
Everything here is from the references shown below, with a few comments in an alternate color.
Figure: Oxygen system schematic, from G450 MM, §35-00-00, figure 1.
[G450 AOM, §2A-35-20 ¶1.] The airplane’s oxygen system incorporates two cylinders or bottles that contain a total of 230 cubic feet of gaseous oxygen pressurized to a nominal 1800 psi. The two bottles are identical and interchangeable, each manufactured from seamless aluminum and coated with Kelvar® fabric to resist rupture. The bottles are designated as crew and passenger supplies, but both bottles are plumbed together into a common supply line just prior to the oxygen system control panel on the copilot side console. Pressure regulators on the bottles reduce system pressure to 55 - 60 psi prior to the supply line to prevent the presence of high pressure flow in the cockpit.
If the tanks are plumbed together why are the pressures sometimes different? I think it is all down to the accuracy of the gauges.
[G450 AOM, §2A-35-20 ¶2.A.]
What do the masks look like when dropping? Here: Oxygen Mask Drop.
[G450 AOM, §2A-35-20 ¶2.B.]
Figure: Oxygen system control panel, from FlightSafety G450 Pilot Training Handbook, page 17-4.
[G450 AOM, §2A-35-20 ¶2.C.] The oxygen system control panel is located on the copilot side console and is divided into two sections. The forward section is labelled OXYGEN SYSTEM, and contains two electrically powered gages that show the amount of oxygen in each crew and passenger bottle, indexed in pounds per square inch (psi). When full, each bottle pressure should read 1800 ±50 psi.
The system selector switch is a toggle switch located below the gages. The switch has two positions: OFF and ON and is labelled CREW / PASSENGER since it controls the flow from both bottles as both are plumbed together. The switch should be selected to the ON position for all flight operations to allow oxygen to be supplied to the flight compartment masks and to the rotary mode control switch for passenger compartment oxygen.
Immediately aft of the OXYGEN SYSTEM panel section is a panel labelled PASSENGER OXYGEN CONTROL PANEL. The panel contains a gage indicating the pressure of the oxygen supplied to the passenger cabin, an annunciator that illuminates the text label PASS OXYGEN ON when the system is in use and a rotary mode control switch to select the type of operation of the passenger oxygen system. The switch has three positions:
[G450 AOM, §2A-35-20 ¶2.B.] Pilot oxygen masks are certified to 40,000 feet and will automatically switch to positive pressurized flow at cabin altitudes above 35,000 feet.
[G450 AOM, §03-03-20, step 41.
Figure: Oxygen system venting, from G450 MM, §35-00-00, figure 202.
[G450 AOM, §2A-35-20 ¶2.E.] The oxygen service panel is located on the airplane’s exterior on the right hand side approximately below the first two cabin windows. The panel is accessible by releasing the locking tabs holding the panel door shut. Within the panel is a direct reading gage for the crew and passenger bottles and a filler adapter. Both bottles are serviced by connecting an oxygen servicing cart to the filler adapter. The bottles are filled by using an ambient temperature vs pressure chart. The nominal full level is 1800 psi at 70°F).
The AFM (G450 AFM, §2-01-20, Step 31) recommends 1,500 psi minimum.
[G450 AOM, §09-02-60 ¶4.B]
How much do you really need?
Figure: Oxygen duration versus cabin altitude, from G450 AFM, §1-35-10, Figure 1-7.
This is an odd chart in that it is based on less oxygen than you really have and completely forgets about the passengers. You will need to venture beyond your trusty AFM . . .
Figure: Oxygen required for de-pressurization and continued cruise, from G450-OMS-02, Table III.
This chart has caused a lot of problems. Let's say you are planning a long oceanic leg where you don't have the fuel to descend to 15,000 feet if you lose pressurization. So you see this chart and say those masks must be good for extended periods at altitudes up to 25,000 feet. Right? What about the following warning?
[G450 OM, §01-35-20, para; C.] WARNING. PASSENGER MASKS ARE INTENDED FOR USE DURING AN EMERGENCY DESCENT TO AN ALTITUDE NOT REQUIRING SUPPLEMENTAL OXGYEN.
I called Gulfstream about this and was told that this chart was intended for use during test flights where the passengers have the same oxygen masks as the pilots. It isn't meant to mean you can plan on using these masks for cruise flight at altitudes requiring oxygen masks.
The formula for converting a cubic foot to a liter is L = ft3 / 0.035315. Which means you have 6,513 liters total capacity. That isn't exactly what the table shows, but it is pretty close.
You can find a similar chart in the G450 Maintenance / Operational / Placarding Procedures Manual, §35, page 35-2. That chart is for a generic GV and the numbers do not match exactly. The numbers shown here are for the G450 and are slightly lower.
Gulfstream G550 Airplane Flight Manual, Revision 27, July 17, 2008
Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.
Gulfstream G450 Maintenance Manual, Revision 18, Dec 12, 2013
Gulfstream G450 Operating Manual Supplement, G450-OMS-02, Extended Operations (ETOPS) Guide, Revision 2, April 2, 2009
Gulfstream GV Maintenance / Operational / Placarding Procedures Manual, Including Aircraft GV-SP (G550/500) and Aircraft GIV-X (G450/350), Revision 8, Nov 7, 2014
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