What is the purpose of the 1/4" vent line? Remember that the headers should
always be full unless you are running out of fuel.
IF you run the tank dry or
if somehow air gets introduced into the header tank, it
must be allowed to escape. The 1/4" line from the top of the header to it's respective main tank is there
only to bleed the air from the header.
nanook is the only person here who has approached the reason for the header tanks.
The following is from CAR 3, the certification basis of the PA-14.
http://specialcollection.dotlibrary.dot.gov/Document?db=DOT-CARS&query=(select+72)
03.422 Fuel system operation.
03,4220 Fuel flow rate.
The ability of the fuel system to provide the required fuel flow rate and pressure shall be demonstrated when the airplane is in the attitude which represents the most adverse condition from the standpoint of fuel feed and quantity of unusable fuel in the tank.During this test fuel shall be delivered to the engine at the applicable flow rate (see §§ 03.42200,03.42201, and 03.42202) and at a pressure not less than the minimum required for proper carburetor operation. A suitable mock-up of the system, in which the most adverse conditions are simulated, may be used for this purpose. The
quantity of fuel in the tank being tested shall not exceed the amount established as the unusable fuel supply for that tank as determined by demonstration of compliance with the provisions of § 03.4221 (see also §§ 03.423 and 03.5222), plus whatever minimum quantity of fuel it may be necessary to add for the purpose of conducting the flow test. If a fuel flow meter is provided, the meter shall be blocked during the flow test and the fuel shall flow through the meter by-pass,
03.42200 Fuel flow rate for gravity feed systems.
The fuel flow rate for gravity feed systems(main and reserve supply) shall be 1.2 lbs. per hour for each take-off horsepower or 150% of the actual take-off fuel consumption of the engine, whichever is greater.
To answer Alex's question of "should there be header tanks in a 150 hp PA-14?" we must look at the STC which approved the installation of the engine, since the original PA-14 engine was an 0-235.
OR is there a subsequent STC which allows the removal (if they were originally installed) of the headers.
This note is part of the TC:
(This would only be applicable to the 0-235 engine installation) The 0-320 must be addressed separately.
NOTE 2.
The following placards must be displayed on the instrument panel in full view of the pilot:
(a)*
(b)*
(c) "Right tank should be used in level flight only."
With this note I suspect that there is NO header tank connected to the right tank. Perhaps there is one for the left tank? OR there is sufficient fuel flow so that one is not needed.
I will add that if anyone has access to Piper's original fuel flow testing results, it may be possible to determine that there was adequate fuel flow on the original tests to cover the flow requirements of the 0-320. I suspect that FAA engineering in Anchorage has access to this data.