Transfer pump function

[albury]

I have a new M7-235C with 20 gal outboard (aux) tanks -- about 35 hours on the plane, no more than a couple hours on each transfer pump.


While moving about 10 gals each side from outboard to inboard tanks, it became obvious (heavy wing, big difference in Aux tank level drops) that left aux pump is moving gas a lot faster than the right one. Both are clearly functioning -- could see response in ammeter from both pumps when in air, can hear pumps running on the ground -- but it appears the left pump is moving the typical 0.6 gpm (?) while the right one demonstrates something less than 1/4 of that flow rate.

Any experience with this? I'm assuming I have foreign material in the right pump or transfer lines that is partially blocking flow and will have to pull pump and/or blow out fuel transfer lines, but I'm hoping there are simpler ideas out there...


And thanks to all of you that post your ideas and experiences -- this makes owning and maintaining a Maule far easier, your input is invaluable.


CGP

[Kirk]

The first place I go, when I start seeing that is to the vent lines. Seems to be very common to have a mud dauber climb all the way up to the check valve and die there.

Bit of a knuckle scraper but you can disconnect the line up at the tank or check valve and blow it out with compressed air.

I finally started putting covers on my vent lines. Made them out of nylon screw covers from the hardware store, attached a ribbon to it.

Kirk

[donknee]

There is a screen in the pump, too. The exposed part with the hex head is a cap which is removed with a push and quarter turn. Seems like there is a screen with a magnet in the bottom and a gasket. You would want to drain the tank first as fuel will run from the pump. This would give you some indidcation of contamination. It should pick up larger particles flowing towards the main tank. Let us know what you discover.
Part of my pre flight check list is to run the transfer pumps for a few moments and the boost, prior to start up. This verifies them pulsing and exercises the pumps.

Check out this link to a previous discussion on this subject:
http://maulepilots.org/forums/viewtopic ... sc&start=0

[Maule 9V]

On preflight I check the vent in the fuel caps for proper operation. On my M-5 the valve in the center of the cap allows me to suck air into the cap but not blow out. If my tip tanks were transfering at different rates, I would swap the caps and see if there was a change. While transfering on the ground, if I open a cap on a tank that is not venting properly, I hear the transfer pump speed up.

[a64pilot]

I don't think the newer airplanes have vented caps, or My M-6 could have the wrong caps on it?
On mine the right transfers faster, but not nearly four times as fast

[Maule 9V]

I called Brian at Maule Parts Dept. He says all Maules use the same type of cap - allows venting in but no flow out. A stuck check valve in the vent line and a non-venting cap could create an interesting situation.

[albury]

Quick update on my experiences so far --

Great suggestions thanks -- I've confirmed not a venting issue (simple but something to think about going forward), so on to checking screens on transfer pump. Looking in Maule manuals to see if there are schematics for how the gas lines are run -- I'm not finding anything. Anyone know where this info may be posted? Tech data on the Maule website?

I do have vents on my caps -- simple check valves. Ball check on the vent line is clear as well.


I'll finish the story when I get it figured out.


THanks again...

[Duane]

call Bryan or Barry tomorrow and they can send you the fuel line dwg in pdf format. Make sure you tell them you have the new system as the older planes have a slightly different plumbing.

[albury]

Update time:

I've checked venting, plumbing, pump screens, suction in outboard tank -- all appear to be normal and transfer pump still moves fuel very very slowly. The pump functioned properly for 2 pumping evolutions then something changed -- pump is essentially new (plane is 6 months old). Next step will be to replace pump -- I hate to spend the $$$ but REALLY don't like the idea of a pump that MIGHT work because of challenges with imbalance -- any final ideas? I appreciate all of the help and thoughts...

[maules.com]

As this change took place when the plane was relatively new, it is possible that residual metal debris from the manufacturing of the tank, has got into the pump pickup line or fitting and partially blocked it. Disconnect the pipe at pump end and blow back into the tank to see if it will clear. Make sure that tank cap is removed first.
Then remove the pipe from outlet side of pump and see if you have clear passage to the main tank, again removing the cap first.
If both are clear and vents are clear, then pump is faulty.

[aero101]

Pumps are available from aircraft spruce for just under $80, cheapest price I've found. Also you should be able to remove the lower cap with fuel in outboard tank without spilling fuel (just residual) as there is a checkvalve in the pump for that purpose when checking screen. If it leaks continuously you have bad checkvalve / or some debris holding it off the seat. If the screen has not been checked regularly, they tend to rust up badly in screen housing area as that's kind of a low point that acts as a trap and if you get any water in sys, it's first place it starts to accumulate? I've seen some screens almost totally blocked with rust particles as this seems to an area overlooked by some A&P's....

[albury]

Finally -- problem solved. Disassembled pump, was fouled with rust decided to replace it, function returned to normal.

Happy about the outcome, I discovered this problem by getting a wing quite heavy and I wouldn't look forward to doing THAT again, especially in the soup.


Thanks to all for help.