PATS auxiliary fuel tank system experiences


I have recently worked on 737NG equipped with PATS auxiliary fuel system. I have found it very hard to get information from the supplemental AMM, and it is not a common system on every 737. Plus if you forget something you have to again remove the tank units.
So I have collected some tips, experience:

1. Before removing Auxiliary fuel cells from airplane perform Vacuum leak check of aft and forward cells. Connections at the L/H wheel well.
2. If no leaks, cells individual leak checks are not necessary.
3. During Vacuum leak check remove restrictor from main drain manifold under cargo floor, cover weep hole at pipe behind ceiling aft of aft tanks/ or forward of forward tanks, cover weep hole at the top of fuel tank core went connection, plug external drain hole.
4. Before installation of  1st tanks check manifold (big pipes) drains properly connected to the drain system and to the manifold.
5. During installation of 1st  fwd tank: cabin pipe connects to the back of the tank and routed over the top of the tanks. Manifold drain pipe routed from top of the tank behind the tank and under the tanks to the cutout of the cargo floor.
6. When installing tanks make sure weep holes at the connection not covered with tape, all the glands and seals installed, only one big seal is installed over the glands at the tanks mating surfaces copper bonding clips are installed.
7. When you sliding together the cells, leave 1-2 feet distance between them, and 3 people ram the cells together. When you hear the ,,clung” metallic noise the cell is properly installed.
8. Use petroleum jelly/vaselin instead of recommended lubricant, provides much better sealing.
9. Before system test make sure that you have enough fuel to test upper limit switch in the center tank. (2 fwd and 3 aft cells configuration auxiliary cells overall capacity is 7.7 tons, refuel airplane total to 13 tons.)
10. During system test use PATS test document TO-753 not the AMM .
11. You can refuel auxiliary tanks from center tank using standard fuel transfer procedures.
12. For the transfer test when using bleed air first use ground transfer switch and after put thee airplane into air-mode. In air mode fueling control panel has still power so you can transfer excess fuel out. to wing tanks.
13. Jacking of the airplane is not necessary transfer is till working.
14. When you have around 100 kgs in the cells transfer is slowing down, 10 kgs per 30 minutes.

Best regards, Balázs

Pats auxiliary fuel tank


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