Originally Posted by stuartcnz
I think that you need to think in terms of the amount of head
, rather than the quantity sitting up there. I'm not sure of the mathmatics involved, but suspect that the size of the fuel
line restricts the pressure, so that the quantity of fuel
doesn't really effect the pressure, except that as the tank is fuller then the head
will be higher, as the head is at the height of the top of the fuel.
metering valve (grey 3" box on the side of the heater) has a float chamber similar to what is in a car carburetor. So the head pressure maintained on the needle valve controlling flow into the heater is controlled by the heighth of the fuel in the reservoir (float chamber). I believe that the height of the tank or the pressure of the pump is determined by not wanting to overwhelm the float valve. Enough pressure will open the float valve against the float trying to close it. If for some reason the float fails in the open position there is an overflow tube in the float chamber. When the oil
level gets above the end of this tube fuel comes out what they call the fuel return line. The height of the float chamber/oil metering valve is critical relative to the burner. My boat had the oil metering valve mounted athwartships. Going upwind on one tack the flow of fuel would decrease greatly, on the other I would get too much. There is a second set of holes predrilled in the Alaska
to mount the oil metering valve 90 degrees around the heater. This worked much better upwind, but it put the valve in between the heater and a bulkhead, making it interesting to adjust.
As to fuel line size restricting flow and dropping the pressure, the flow rate is way to low for there to be an appreciable pressure drop for this size fuel line, but either way this has nothing to do with the operation of the heater. As long as enough fuel gets to the float chamber to maintain a constant level of fuel in the chamber, the pressure in the fuel line is irrelevant until it is high enough to overcome the normal operation of the float valve.