Gascolator Leak

[170C]

On our gascolators, the brass valve we use to sample the fuel for water----mine didn't want to stop dripping this afternoon. Pulled the bowl off & couldn't find any debris in it. The brass valve didn't seem to want to come out of the base of the unit so I left it and reinstalled. It took several times to stop it from dripping----first time I have had this problem. Is there a "O" ring in that valve? What is the best method to stop a leaking valve?

[Bruce Fenstermacher]

Frank,

Yes there is or should be an o-ring or something that looks like an o-ring depending on the model of valve you have. You should have been able to see this so I wonder what is left of any seal in yours.

Now the reason I say it might look like an o-ring is that it may in fact not be. If it is a valve manufactured by Curtis the seal is a round seal with a flat side. It is NOT an o-ring. Curtis does not sell the seals (they use to) and they are not available. I think they feel that with their design when the seal stops working it's time to replace the whole valve.

If you have a Saf-Air valve, they use a common o-ring. But it is not so common that folks have them in stock unless they ordered them specific.

Now you might also have a Koehler valve. I can't tell you what seal these have. One for the Saf-Air valve may work. I just replace them with a new valve and I prefer the Saf-Air brand so that I can replace the seal with new which I keep a stock of.

Now you were real smart to just put the thing back together when the valve did not come out. You need to be VERY careful how you remove the valve. First and foremost protect the gascolator part because it will cost the most to replace when you ruin it. Putting a twisting torque on the valve body which in turn twists the gascolator base can easily twist and warp the base and you will never get the gascolator body to seal against it. Don't ask how I know this. Holding the base securely around the entire circumference is the key.

If the valve you have has a brass body chances are you will ruin the valve body with the wrench you are using to remove it. After all traces of gas are removed and at a safe distance from your airplane I'd use a heat source such as a heat gun to heat the gascolator base to expand it. Don't heat the base so hot in one spot so that you warp it.

Helps to price out a gascolator before attempting this valve removal so you can judge how careful and patient you want to be.

[GAHorn]

It's probably a Garwin gascolator (or, as Bruce inferred, might be anything some subsequent owner installed.)

If your gascolator is original it will be one of these. (Frank, I believe your converted 172's serial is 28988 ):

click to ENLARGE click a SECOND time to further enlarge

As you can see, there are three different valve sub-assemblies used by Cessna. Item 14 is a simple, manually-rotated valvebody which is not illustrated in any exploded-diagram. It has a small o-ring at the finger-lever which is unspecified, and very difficult to replace without damaging the valve. I suggest you replace it with a Saf-Air or Curtis valve.

Item 15 is a remotely-operated Curtis valve which uses o-rings (not specified by Cessna but supplied by some vendors under a Curtis PN).

The unidentified valve sub-assembly (on the left in the pic) is likely the original on your aircraft, a remotely-operated valve which uses an o-ring also. It is a MS29513-7, and sits on top of item 18 (plunger) which is operated by a rotating cam (item 19, shaft).

Here's the complete, two-page IPC illustration and parts-listing for C-172 aircraft, serial 28000 thru 17249544, which should cover your aircraft if I'm correct as to your year model.

172Gascolator.pdf

(404.83 KiB) Downloaded 420 times

A good way to get the valve removed from the gascolator is to shut your fuel selector OFF, and fill the gascolator with penetrating oil (such as PB Blaster) and let it soak before attempting to remove the drain valve from the lower gascolator body.
The lower body is aluminum and the valves are usually steel, so corrosion sets up at the threads, which are also sometimes "Pookied" in place with sealant. Use wood blocks to hold the lower body in a vise while unscrewing the valve. Use Permatex No 2 to seal a couple of the threads when you re-install it. (NEVER use teflon tape in a fuel system.)

[Robert Eilers]

Some time back I had the same complaint about a dripping gascolater valve. One of the 170 forum members (sorry can't remember who) recommended placing a little fuel lube around the top of the valve (the part inside the gascolater). I did this and have not had a drip problem since.

[170C]

When cleaning my gascolater I didn't look to see what its mfg was. Next time I have it off I will do so. The valve appears to be brass------at least it brass colored. It is not any of the valves depicted in the drawings. (serial# is 28988 as you mentioned George) It has a short "lever?" that you push up to allow gas to flow from the gascolator or you can lift it up and to one side and it locks it open. I think that is similiar to the Curtis brand sump drains. As Bruce mentioned, I sure don't wish to have to purchase a new gascolator. Geeze they are proud of them and none of the supply houses that have their catalogues have ones like we have on our birds.. I imagine the ones they do have would work, but I like being able to see the fuel in the glass. One might have to search out the salvage yards to find what I/we currently have. If mine starts leaking again I may try putting the suggested oil in the gascolator to see if it helps. As best I could see with the glass still attached to the bottom of the base, I couldn't see an 0 ring gasket and I didn't want to try to remove the glass from the base an maybe create another possible leak. I assume my glass bowl was just stuck to the rubber gasket at the bottom of the base.

[Bruce Fenstermacher]

Frank,

Making my comments, I forgot you had a 172 with the fancy pull cable thingy. But the valve will still have a seal and the important thing to know is it may might be a standard o-ring or it might look like a standard o-ring but isn't. You will have to get the model of the valve before we can figure that out.

[170C]

No Bruce, my 172 is not new enough ('56) to have the cable pull on the gascolator. Its the same unit as would be found on later model 170's. Basically if you ignore the tail feathers and the fact that the firewall has a doubler where the nosewheel bracket was attached its the same identical airframe as B model 170's. As an aside, I don't understand why the newer 100 series of Cessna's have the gascolator drains which you activate by pulling a knob. You can't check the fuel on those (at least some of them) because the drain line from the gascolator is on the opposite side of the engine from the drain knob. I suppose Cessna figured you only needed to drain fuel to rid it of any water or foreign matter and didn't need to be able to see it or collect it for inspection

[15A]

Basically if you ignore the tail feathers and the fact that the firewall has a doubler where the nosewheel bracket was attached its the same identical airframe as B model 170's.

Are you out of your mind
Your not trying to convince these guys that us 'converters' are really the same, are you?

[170C]

Well Joe, if we don't tell them they are the same they will get really jealous and try to buy our birds and most of us don't want to do so. Especially George------he really wants a GREEN plane

[GAHorn]

Well Joe, if we don't tell them they are the same they will get really jealous and try to buy our birds and most of us don't want to do so. Especially George------he really wants a GREEN plane

That's OK, Frank. Go ahead and try to get me all riled up.
For when you break that expensive Garwin gascolator trying to unscrew that drain valve....
...you'll be sucking-up however much it takes to replace it with what brand-new/NOS is sitting in my spare-parts bin...

[170C]

You are most likely correct George Where is the brand name for the gascolator? I can't see mine very well with the cowling installed. I know its not on the bottom of the unit. PS: Did you happen to notice the color of the writing on the gasolator you have in that photo Sure would match my plane

[15A]

"DITTO"

[GAHorn]

... Where is the brand name for the gascolator? ...

It's on the opposite side of the bail from where all that FAA/PMA/Inspectors rubber-stampings are...on a stick-on aluminum tag which has likely fallen off yours. ( GREEN things have a way of getting lost in the dust .)

[170C]

Geeze, as popular and politically correct as being GREEN is these days, it sure is hard to get any respect Now I know how Rodney Dangerfield felt (Wonder if one of those old tractor fuel/sight glasses would work--hmmm )

[GAHorn]

Unfortunately, most of the tractor gascolators have a different bowl.