What can anyone tell me about replacement fuel drain valves or fuel sump valves, and the o-rings used to install them, for our planes? How about repairs to the existing valves?
The O-ring mentioned in some prior postings (MS-29513-17) is not internal to the drain valve, but is instead the ring that seals the drain valve to the wing. Fact is, the parts book is wrong on this part number; it says to use the -17, but that ring is much too small. If you call Beech Tech Support, they will tell you that a -20 is the correct size. A -18 has the best fit, on the post-type drain valves. I have not confirmed it, but it is possible that the early valves need the -18 while the later flush valves need the -20. From my experience, the -17 doesn’t fit any of the valves.
Not to say that there are none out there, but I haven’t run across any of the T-type (non-flush) drain valves (PN 967B1A) that were repairable… and if replaced with the same type (originally made by Auto-Valve), they cost a small fortune. They list for $232 from RAPID (and they do have some), but Arrell Aircraft may offer them for less:
http://www.arrellaircraft.com/
There is one thing you can try, to salvage them for a while longer. Drain the tanks, remove the valves, and polish the moveable portion of the barrel with crocus cloth (a very fine red-colored sandpaper). Then apply a trace of LPS-2, and reinstall them with a new O-ring base seal. From that point onward, on about every other flight, spritz a tiny bit of LPS2 into the joint where the moveable barrel slides up into the valve body. The LPS-2 won’t leave any residue, will not harm the internal seal, and will wick up into the area of the seal. If your drains don’t presently leak or stick, this practice can greatly extend their useful life. You are wiping your prop’s leading edge with LPS-2 (or equivalent) after each flight anyway, right?!
I’m pretty sure (per the parts book) that the later years of all models (basically from MB-866, M-1971, and MC-537 onward) used a flush fuel drain, PN 971D1. With the same Type Certificate (A1CE), the same physical attributes, and the near-universal applicability of the fuel drains to all models, the flush valve ought to be legally useable on all model years.
The Beech 971D1 flush valve looks very similar to the Model F75 Saf-Air TSO-C76 aluminum flush valve fuel drains, that fit most Cessna twins (310 through 441). The F75 functionally replaces the Auto-Valve #971D and #971D1 (the flush valve used on the later models of our planes). These aluminum flush drains have the large 3/4-16 SAE running thread, with the same O-ring seal at the tank surface. The F75 comes with an MS29513-020 o-ring for the base seal. I don’t know their current price everywhere, but the last I saw them at Sun-N-Fun they were around $60 per pair, and were extremely well made. Unlike some original valves, it is impossible for them to come apart in flight. Here is a link to Saf-Air; you can view the F75 near the bottom of the page:
http://www.saf-air.com/fuelv.html
Aircraft Spruce currently sells these for $54 each:
http://www.aircraftspruce.com/menus/ap/fuel_drainvalves.html
If you look into these TSO’d replacement flush drain valves, which should be able to be considered standard replacement hardware due to the TSO compliance (it is stamped right on them), I have one cautionary note. On some of the earlier planes, you may find that the nut on the fuel feed line (inside the tank) has a partial interference with the larger body on the new drain. The F75 has the large diameter threads the full length of the body. In the later years Beech either slightly changed the fuel port location, or re-oriented the line nut to clear. Just make sure that you can run the drain down flush to the new base O-ring (you’ll use a new o-ring, right?!) without interference; don’t force it with a wrench. You can actually look up into the threaded fitting opening, and get a good idea of whether you’ll encounter any interference.
If you have a slight clearance problem, someone somewhere might mention some slight filing on the OD of the valve body, down to the base of the threads, at the top where it might interfere. It is very “meaty”, and taking off the threads for the last quarter-inch has no bearing whatsoever on the strength or retention of the valve. That portion of the threads is well above the threaded wing tank drain fitting port, and is up inside the tank. You can also consider removing the fuel level transmitter, to reach in and re-orient the flats on the line nut.
Keep in mind that you’ll need to use the pin-style sumper set-up if you convert to flush fuel drains. The same pin sumper style will still work with the T-style gascolator drain valve. You’ll also have to just unscrew your drain valves over a large metal funnel, should you have to drain your fuel tanks (use a bonding jumper!). But after all, flush fuel drain valves ought to be good for at least 1/25th of a knot in drag reduction, right?! It can’t all just be “about money”….
From Oz:
If you are thinking about replacing the drain valve o-ring, no need to completely remove the drain valve. Unscrew it just enough to pry the o-ring out, maybe 4 or 5 turns. Replace the o-ring, using some Parker O-Lube or the same Dow Corning DC-4 silicone grease you use on the oil filter, and screw it back in. If the internal nut turns, you have to take the fuel transmitter out to gain access. You can then reach the top-side of the nut with a screwdriver or fabricated tool, and hold the nut. While the transmitter is out and the tank is dry, not a bad idea to vacuum it. There was about half a tea spoon worth of crap in mine.
CAUTION! THERE WILL BE FLAMMABLE VAPOR IN THE FUEL TANK! BE CAREFUL ABOUT STATIC, AND SPARK-PRODUCING TOOLS!
I finally got my leaky fuel drain valve fixed. I’m posting this message so that others can learn from my experience. It was leaking about 12 to 16 ounces per week. The early planes use a T-pinned extended valve, while the later models use a flush drain valve; both are manufactured by Auto Valve Corp., exclusively for Raytheon-Beech. Both valve types are very expensive from RAPID. The extended valves are essentially unrepairable; however, it is fairly easy to fix the flush valve, for under a dollar.
If you decide to remove the valve, first defuel the tank. Unscrew the valve by using a specialty socket that you fabricate yourself. Do not unscrew using a screwdriver; it can damage the valve. Fabricate a socket with two pins sticking out. You’ll see what I am talking about once you look at the valve. The outer larger diameter o-ring is MS29513-020. It is available through RAPID for 17 cents (in Oct 2004). It is not available at Aircraft Spruce. You will also need the smaller internal o-ring that goes around the movable shaft. It is MS29513-010. (Editor’s note: the correct size for the inner ring on the post-type valves is an MS29513-011; and the best-fitting size for the outer ring is the MS29513-018. Oz’s comments apply to the flush-style valve).
Do not dismantle the valve to remove and install the o-ring on the shaft. Be patient and pry the old one off, and work the new o-ring in (use the o-ring lubricant). That’s it. Screw the valve back into the wing. If the nut spins inside the nutplate inside the tank (it happened to me), no problem. See above about holding the nut from inside the wing.
Have your work checked by an A&P. Fill up the tank and check for leaks. Also inspect the area around the fuel transmitter before installing the upholstery panel. If you don’t see bonding straps/ground wires between your transmitter and the airframe, read the BAC FAQ on fuel gauge and transmitter bonding, to improve gauge accuracy, before closing things back up.
NOTE! The center shaft of the valve assembly is designed to move up to allow for a sample. However if pushed up aggressively and unexpectedly twisted, it will lock in open position. The center shaft locks at every 90 degrees. Simply push up and twist in either direction to unlock. I prefer using the test-tube type fuel tester with screwdriver tip on one side. If you accidentally get the drain valve stuck open, the screwdriver comes in handy to quickly twist and unlock.