Mystery Hose

[TinyTrains]

I just finished replacing the filter sock and vibration boot on my K75 fuel pump. What is the purpose of the vent hose from filter sock to the top of the tank?

What are you venting?

Just curious.

Scott.

[Zagando]

Vent hose from the filter sock?:bolt:bolt:bolt
Could you be confusing the fuel line from the pump to the filter, perhaps?

There is no vent from the sock as it is submerged in gasoline.

[TinyTrains]

Item 15 below. It connects from the bottom of the screen to a pipe at the top of the tank, which I believe is open to the double wall. It is a non-pressurized hose. I have seen it listed as "vent hose". Item 8 is the fuel line.

http://home.pacbell.net/schifer/pump.jpg

[Zagando]

Very puzzling, at least to me (I have a later model with a different style pump; no hose near the fuel sock at all). Perhaps Paul or Lee or Don will chime in with the answer soon. I'll stay tuned to find out what the heck...:scratch

[roncooper]

There is a possibility of the fuel boiling, and the vent is there to carry the vapor up so that the pump has liquid to pump.

[Gilly]

It's been awhile since I've been inside a K fuel tank (or my HAND actually, not ME!), but I believe the one that goes to the top of the tank is just the hose for the water run-off hole, which is situated to one side of the fuel cap, it carries off rain and wash water or spilled fuel, through that hose in the tank, to the bottom of the tank, then through that collector cup it runs to the ground, where it lubricates your rear tire and makes you wipe out. or something like that.
Gilly

[scjack]

I've replaced a couple of fuel pumps on K100's. It's been about seven years since I've done one but I believe that it's the scavenger hose. It's purpose is to pick up any gas that doesn't work it's way down to the bottom of the pickup for the fuel pump.

[Gilly]

What is the purpose of the vent hose from filter sock to the top of the tank?



The one that goes to the TOP of the tank is the water run-off hose. I don't believe there are any other hoses up on top. I can't remember where the one that attaches to the strainer goes, though. "Hoses to nowhere"? maybe picks up fuel from a low part of the tank? I'd check for correct routing, just to be sure. If that attaches to a nipple below the hole that you see in the notch in the fuel cap, and it's running to the strainer basket, I think you have a problem. It's supposed to attach to another nipple in the bottom of the tank, which spills into that plastic collector cup.

Gilly

[TinyTrains]

I think roncooper has it. Should a bubble form in the screen, it allows it to vent up rather than cause cavitation in the pump. The hose definitely connects to a nipple at the top of the tank's inner wall, which has nothing but air. The hose was added in 1985 and up. BMW added it to resolve some problem no doubt.

The filler ring drain is a metal pipe that runs from the top of the tank and out the bottom.

Thanks,
Scott

[Zagando]

Scott, I think you and Ron nailed it. Thanks for the enlightenment. Now I wonder why my '94 doesn't have such a hose. Perhaps because the possibility of my gas boiling is much less with the underside tank insulation that is in place? It is a different style of pump, though so maybe the problem was remedied in another way.

I used to have a '85 K100RS that made the gas boil in a hot climate (at least on one occasion)---probably had that same hose as yours for the vapors!

[TinyTrains]

It may not be just boiling, but an air bubble getting trapped when the tank is low and the fuel sloshes around. The screen is VERY fine, and the surface tension of gasoline may be enough to trap a bubble.

Thanks for all the input.

Scott