PA-28 and PA-32 Series Part 1: Fuel Tank Removal
Most Piper Cherokee owners will be faced with repairs to the fuel tanks at some point. Cherokee tanks typically give years of trouble-free service, but like all fuel tanks, they do require maintenance from time to time. The following article explains the steps that an A&P follows to repair a fuel tank. Of course, an owner can assist with A&P permission and supervision and learn a great deal about the plane in the process. Part 1 covers removal of the fuel tanks. Part 2 will cover reinstallation of the repaired fuel tanks.
Fuel Tank Design and Construction
The PA-28 and the PA-32 series of Pipers use the same type of metal fuel tanks. The tanks vary in size on some models, but the construction is similar. These fuel tanks are metal tanks that are part of the wing structure. They are held in place with structural screws attached to nut plates on the top and bottom of the wing spar and to nut plate strips on the edges of the adjacent wing ribs. The front of the tank is part of the leading edge of the wing. One of the advantages of this design is that removal of the tank gives lots of access to the interior of the wing for inspections or maintenance on other parts of the plane.
The tank assemblies themselves are made of aluminum and assembled with solid rivets. Each seam is precoated with a fuel-resistant two-part sealant that is allowed to dry and cure once the assembly is complete.
If a tank gets damaged, it is difficult to replace it with a different one from a salvage yard, even if they have the same part number. The fuel tanks, along with the wings, were hand-drilled at the factory when they were manufactured. That means that the tanks from one wing will not usually interchange with other tanks because the screw holes on the tank will not align exactly with the receptacles on a different wing.
Tank Repair and Resealing (No Sloshing Allowed)
Most mechanics send tanks to shops or repair stations that specialize in fuel tank repair for disassembling, inspecting, repairing, and resealing. Most repair or reseal work requires major disassembly of the tank because the only direct access to the inner part of the tank is either through the filler neck or through the small opening for the fuel quantity transmitter. These openings are too small to allow access by a person’s hand or tools.
The process of “sloshing” a tank to seal a leak is no longer allowed. Tank sloshing involves coating the inside of the tank with a thin sloshing compound. Once the compound is poured into the tank, the tank is rotated or bumped so that the compound sloshes around inside the tank until it is coated. It leaves a thin coating of sealant on the inside of the tank once it has dried. The dried compound can eventually flake off the inner surfaces of the tank and clog up fuel filters and fuel lines, possibly starving the engine of fuel.
Many years ago, Piper had a sloshing maintenance procedure and a sloshing compound with a Piper part number, but it has since disallowed its use. Service Bulletin 251D addresses that issue.
Also, Piper Service Bulletin 1006 for spar corrosion inspection has a specific warning in the fuel tank inspection portion that any use of sloshing compound is prohibited, and any evidence of sloshing compound requires its removal from the inside of the tank.
There are some slight variations in the tanks and the way the fuel lines are connected, but for the most part, the tank removal is similar for most Cherokee models. The PA-32s with two metal tanks in each wing have two interconnect tubes with rubber hose connectors. The removal procedure for these tanks is much more complicated than on other models.
Preparation for Tank Removal
Before pulling a fuel tank, it’s best to put the airplane wherever it needs to remain while the tank is out. The fuel tank is structurally a part of the wing. Once it’s removed, essentially a chunk of the wing is missing. Therefore, many shops place the airplane in a corner or someplace where it won’t have to be moved while the tank is out. This is especially true if both tanks on the same wing are pulled on a PA-32.
The next step is to place the fuel selector in the off position and begin draining the tank by opening or removing the tank’s fuel drain valve. If the fuel is to be reused, then it needs to be drained into clean containers.
It is a good idea to put masking tape and paper around the tank edges on the wing itself. Once the screws are out and the tank is loose, the edges can accidentally get shoved up on the surrounding edges of the wing and mar the paint.
Fuel Hoses and Connections
A steel braided fuel hose connects to a fitting on either the inboard side or rear of each inboard tank. There is usually an access panel that allows enough room to disconnect the fuel line. The fitting in the tank that the line connects to sometimes also must be removed because it protrudes too far to slide past the rib as the tank is slid out during removal. On some models, the fuel line connects to the rear of the tank on the inboard side. On these models, the fuel hose can be disconnected from the airframe side and the hose and fitting pulled out with the tank.
Dual Metal Tanks on PA-32s
The dual metal tanks on PA-32s are connected with a large 2-inch diameter aluminum tube (interconnect tube) attached to each tank with rubber hose couplings and clamps. (Piper sells theses hose pieces with Piper part numbers.) This allows both tanks to be filled through the filler opening on the outboard tank. There is a 3/4-inch diameter aluminum tube connected with rubber hose couplings and clamps near the top of each tank. This allows both tanks to use the same vent. These tanks are far more difficult to remove than the Piper models with a single metal tank or a metal tank and fiberglass tip tank in each wing.
The interconnect tube and the tank outlets and inlets are made of aluminum tubing. The ends of each tube have a bead that the hose couplings have to slide over. A hose clamp is used to secure the coupling on the tube and tank outlets. There are small holes near the tank corners on the bottom of the wing that have a metal hole plug over them. The holes are there to allow access for a tool to slide through to loosen the clamp. The clamp can be hard to access if the last installer didn’t orient the clamp correctly. Sometimes the tank corners are sprung where previous mechanics have pried up the corner of the tank to access the clamp.
The hose couplings are thick-walled and must stretch to slide on or off past the bead on the tube or tank outlet. These hose couplings dry out and become hardened and brittle over time, losing all their flexibility. They generally have to be cut off with a razor knife. This is a difficult process because there is only one small access panel to work through. Only one arm and hand can fit through the access hole, so most of the internal work must be done one-handed.
It’s difficult to cut the hose couplings off without the razor knife making scratches or deep gouges in the aluminum tubing. If the interconnect (cut out or “vent”) lines are damaged, they should be replaced. The aluminum tubing inlets and outlets on the tanks are riveted on, and they should be replaced as well if they’re damaged. (The repair shop that reseals the tank would replace these.)
The wing tips must be pulled to remove the outboard tank. The fuel vent hose connection can only be accessed through the outboard end of the wing. The fuel vent fitting that’s screwed into the tank itself also has to be removed in order for the outboard tank to have enough clearance to slide out of the wing.
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