Forum: F-16 Procedures

Henkster, to correct your theory of how the externals fill is that they usually fill up last. The internal Aft/fwd Res fill first then on out to the A1 and F2&1 cells then the wings, then the external wings fill and finally if it is installed the centerline tank fills. Usually when I've had jets vent on me they had centerlines installed. And if I'm not mistaken in my dealings with fuel shoppers they have always told me that the shutoff floats in the internal wings shuts off when the wings are completely full usually within 5-10 gallons of full capacity. The above sequence can be found in the 28FI & GS as well in the 7-lvl CDC's but go off of the T.O.'s as they are more acurate.

F-16.net Sponsor

Actually the remote sensing pressure relief valve is what will dump excess fuel overboard during ground refuel to keep tanks from over filling, it also backs up the V&P valves during pressurization. The sound you hear during refill is the RSPRV spewing air pressure being pushed out by the fuel.
Regarding the external tanks, the internal and external tanks all fill at the same time starting with the reservoirs, the internal wings fill last as that is where the high level float is located.

hence the name toilet bowl........

Man I haven't hear that one but a classic analogy regardless.

F16and117DCC wrote:

Henkster, to correct your theory of how the externals fill is that they usually fill up last. The internal Aft/fwd Res fill first then on out to the A1 and F2&1 cells then the wings, then the external wings fill and finally if it is installed the centerline tank fills.

When the refueling process starts, as soon as fuel routes through the refuel manifold, fuel also goes into externals (if installed). They fill up simultaneously with the internal tanks. The internal wings are last because the high level shutoffs (floats) are in the internal wings.

sorry Happy, I failed to read your previous post and basically wrote the same thing.... sorry, I had a bit too much to sniff tonight (fuel)!

Guys,

Thanks for the refreshing on fuels.
Come to think of I do remember the remote sensing pressure relief valve is what the makes the sound.

I had a few airplanes dump fuel on me but I can't remember if they had wing pylons or centerlines.

Anyway thanks for the info.

greetz henk

I hear ya brutha, had a few myself but it wasn't jet fuel, kinda of tasted like it though.

Newbie Joined: Oct 25, 2005 - 11:05 PM Posts: 2

What, the job of the internal and external V&P's are to pressurize the internal & external fuel tanks. The internal and external V&P's vent the fuel overboard because fuel fills up the vent box, and has no where else to go except... overboard.

um.... no Diedrich i believe there is only two components to make the externals overfill is either a faulty R&D, or float. It could overfill statically if the internal pressure was applied (ex. after refuel) and the float valve was leaking, but it would take a while to fill that much. By the way, congrats on making Tech

RAM ON!!!!!

bobr i am ramming on and enjoying balad. This was a question just to make sure that inorder for a tank to overfill. It would req the tank to be bad. I could not come up with a way for a tank to over fill without the tank being bad.

ive seen a jet overfill 2x with no problems to the jet. when we first got to balad fule truck driver was a little bervous and even with fuel pouring out of the wing vent he kept pumping. no problems with the jet we released the system of pressure and opened the depuddle points to release some fuel and it was good. the next time was during an ORE when we went from mopp 4 to mopp 2 he was taking his mask off and kept pumping acft vented out of the wing vent...this time it did blow a seal on the standpipes so we had to R2 the tank due to the leak

There is never suppose to be fuel in the vent tank since this is where the system pressurization begins and hence the reason for the RSPRV. The vent tank is typically a dry bay but if sh!t happens the RSPRV relieves pressure/dumps fuel at 7-9 psid since the internal V&P valve isn't working with power off, there’s no power to it. Like I stated before, it's the woosh whoosh sound you hear during ground refuel.
With power on or in flight there is a vent tank float valve, it shuts off all external tank transfer if the vent tank starts getting gas, but it only works if the external tank transfer switch is in NORM. Put that baby in WINGS FIRST or CFT/NO FILL, game over.

Happy Gilmore, The internal V&P does work with power off, it is not energized unless the the IFR switch is on or the Tank Inerting swith is on. In normal operation, the internal V&P is never energized. So power to the aircraft does not effect the internal V&P. The RSPRV (toilet bowl) is only a back up to the Internal V&P, if the Internal V&P failed to vent like it's supposed to and you didn't have a RSPRV, there would be big problems. Also, the External tank transfer switch is only tied in to the low level floats in the external tanks, not the float switch in the vent box. Wings First position overrides continuity to the low level float in the center line and turns it over to external wing tank's low level float. The external tank transfer switch does not tie into the float switch in the vent box. Please correct me if i'm wrong, after all, that's what this site is for.

cchief16, sorry, you are dead wrong. If a jet vents during refuel, something's bad, if your toilet over flows in your home, somethings wrong with the toilet, don't blame the water tower.

I'm going to enjoy this because your nuts bealio.
Dude you need to go back to Fuel System School, for one thing during refuel there is no power on the internal or external V&P valves, the whole system works off of differential pressure.
There is no "ON "switch for the IFR switch, it's either OPEN or CLOSE. The tank inerting switch also doesn't have an "ON" or "OFF" switch, it's either "OFF" or "TANK INERTING".
Do you really think the vent tank float is not tied in with the external tanks with power on? You’re crazy.
Two questions:
1. Tell me everything that happens in flight when the IFR switch is placed to OPEN and I'll kiss your a$$.
2. What happens when the tank inerting switch is placed to "INERT".
Gotta also ask this simple question, what is the PSID of the internal and external tanks, what’s the function of the negative pressure relief valve, jeez while I’m on the subject what is PSID?
If you have any reasonable answer for any of these I'll shut the Hell up, then I’ll explain to you how the system really works.

Happy Gilmore, you are right, the internal and external v&p valves are not powered during refuel, unless it's during a hot pit refuel. The internal and external are also not powered during normal operation. The internal v&p is only powered during IFR or tank inerting. The external v&p is only powered during IFR. I'm sorry i was not more specific with the switch labeling, i thought you would understand. I know the float switch in the vent box is tied in with the external tanks, but the float switch in the vent box is not tied in with the external tank transfer switch.

Question #1. IFR switch is place into the "OPEN" position. 3,000 psi hydraulic pressure from system B opens the IFR door. Internal and external v&p are energized. Internal pressure drops to 1-3psi. External pressure drops to zero. The ready light comes on, the indicator is to the right of the HUD. External IFR lights come on as well as some lights in the IFR bay. If you want me to be more specific, let me know.

Question #2. Tank interting switch is place in "TANK INERTING". Internal V&P is energized. Internal pressure drops to 1-3psi (combat pressure). Halon will enter the system through the v&p's. As far as the halon shutoff valve B and the halon control valve, i'm not sure when those come in to play or at what times.

Simple Question #1. 4.7-6.4 and 19-24.
Simple Question #2. When the outside pressure is greater than the internal pressure, the negative pressure relief valve will allow outside pressure into the system, it will prevent imploding. It will open at 0.75psi.
Simple Question #3 Pounds per Square Inch Differential

I don't know how specific you wanted these answers, but if you have anymore question, feel free to ask. I still disagree with your original statement and would like you to prove me wrong, pointing out typo's will get us no where. Please read my entries more carefully, you're putting words into my mouth.

My disagreements are... you say the internal v&p doesn't work with power off, i say it does. You say the float switch in the vent box does not work when the external tank transfer switch is in wings first, i say it does. Please point on these issues. Thank you!

Forum: F-16 Procedures

External fuel tank over filling