CRJ 200/700 Pressure fueling vs gravity fueling
- Thread starter g4downin
- Start date
TFaudree_ERAU
Mashin' dem buttons
My guess is that the function of the floats (assuming the CRJ has float type cutoff switches like the Challengers) is designed so that the system shuts off before the tanks are completely full, ensuring the system doesn't develop an excessive pressure if the truck keeps pumping into a full tank.
With gravity (overwing) fueling, only the EPA really cares if you spill a little bit when it overflows. With pressure fueling, I suppose it's possible to not only damage the internal plumbing of the airplane, but also the truck.
With gravity (overwing) fueling, only the EPA really cares if you spill a little bit when it overflows. With pressure fueling, I suppose it's possible to not only damage the internal plumbing of the airplane, but also the truck.
Krieger
Well-Known Member
I'm just going to guess too....
When pressure fueling at 90 gpm (gallons per min.) if the fuel system pre-check failed or was too slow to turn the system completely off you could have a fuel spill on your hands. So a buffer zone of sorts.
I'm sure the higher fuel load from an overwing fueling are common. Whether its in the book or not.
Example: next time you take your Lear 60 to Hawaii, pressure fuel it to a top off, and then squeeze as much fuel in as you can overwing.
When pressure fueling at 90 gpm (gallons per min.) if the fuel system pre-check failed or was too slow to turn the system completely off you could have a fuel spill on your hands. So a buffer zone of sorts.
I'm sure the higher fuel load from an overwing fueling are common. Whether its in the book or not.
Example: next time you take your Lear 60 to Hawaii, pressure fuel it to a top off, and then squeeze as much fuel in as you can overwing.
g4downin
Well-Known Member
It is also compelling to note that both the 200 and the 700 have a greater fuel capacity when they are pressure fueled. The exact numbers for the 200, for example, are:
Pressure Fueled left wing usable fuel: 4760 lbs
Gravity Fueled left wing usable fuel: 4488 lbs
TFaudree_ERAU
Mashin' dem buttons
Where are the overwing fuel caps? If they're not all the way out on the tips, you'll lose that much capacity because of the dihedral of the wing.
N519AT
Ahh! This is how I change this!
This could be because the overwing port is located in a position such that it is lower than the "top" of the tank.
Here's a picture of a cross section of a generic fuel tank. If the X is the overwing port, you will see that it is lower than the fullest portion of the tank.
So, if you top the aircraft off via single point (pressure refueling) and then open the overwing port, you're going to have a spill on your hands. I believe the 757 is prone to this situation.
Maybe we're talking about the same thing, but it has always been my understanding that the high level fuel SOVs on any aircraft are there to prevent fuel spilling via the vent when the tank gets full. The idea is to shut off the fuel flow via the internal valves on the aircraft to prevent the fueler from continuously pumping when the tanks are full to prevent the excess fuel from going out the vent and onto the ground.
I believe that on some aircraft, there are sensors installed on the piping that read the pressure, and if the pressure is too high (generally above 50 psi) the valves will close and the system has to be reset to fuel again.e
On the MD-80 and DC-9 series, the fuel vents are located at the outboard section of each wing and the fuel panel is underneath the center forward part of the right wing. The way that the panel is situated, the main landing gear blocks your view of the left vent. The worry, as stated above, is that you have a faulty fuel SOV and you keep pumping into a full tank. This problem is compounded by the fact that if you're pumping into the left tank, you can't readily see the left vent. Fueler keeps pumping into a full fuel tank, with a faulty SOV and fuel goes everywhere until someone tells him he has a fuel spill. I've seen the results of this first hand and it usually makes a big mess everywhere.
BobDDuck
Island Bus Driver
I would guess that most ground school instructors at most RJ operators would have to go searching for that answer. You probably won't learn anything about it, unless you ask.
The reason (as stated) has to do with the position of the gravity refuel caps. They sit relatively far inboard and the fuel cell goes upwards out into the wing so it isn't possible to gravity fill all the way to the top of the fuel cell. With pressure refueling the pressure from the hose will push the fuel all the way outward into the wing tanks.
