The Cessna 120-140 Association Forum

I have a 1947 C140 with a o-200-a/SA547EA STC.

The Univair U0411716-500 fuel valve has an engine eligibility list that only covers the C85/C90 (TCDS E-252) family of engines and does not include the O-200-A (although this engine does use the same TCDS as the C90).

The advice I received was to verify if the STC requires any modifications to the fuel valve. If not, the PMA should apply, and the installation should be legal without needing any additional approvals.

Does anyone have the STC instructions, and does the STC require any modifications to the fuel system/selector valve?

-Ryan

First things first.

I don't recall anything on the engine STC's regarding fuel selectors.

Second, the valve you are talking about is a Left on/Right on/Both off valve.

Do you have the crossover vent between the tanks? That's a different story and a different valve.

I'm confused. First, the C85 and C90 are different TCDS's.

Second, the fuel valve is an airframe component, not an engine component. My take is, if the O200 STC does not require any changes to the fuel system, then, if the valve is STC'd or PMA'd for the airframe and the O200 was properly approved, then you should be good to go.

You cannot use a valve with a "Both" position on a plane that doesn't have a line connecting the air spaces of the two tanks, but there is no functional reason you could not use a valve that doesn't have the "both" position on a system that does have interconnected air spaces.

6643 wrote: ↑Thu May 01, 2025 7:49 pm I'm confused. First, the C85 and C90 are different TCDS's.

Second, the fuel valve is an airframe component, not an engine component. My take is, if the O200 STC does not require any changes to the fuel system, then, if the valve is STC'd or PMA'd for the airframe and the O200 was properly approved, then you should be good to go.

You cannot use a valve with a "Both" position on a plane that doesn't have a line connecting the air spaces of the two tanks, but there is no functional reason you could not use a valve that doesn't have the "both" position on a system that does have interconnected air spaces.

I misspoke (typed?) the instructions for the valve lists engine eligibility for TCDS E-233/E-252/E-223 to cover the C85, C90, and O-235 engines.

This valve does not have a 'Both' selection, as confirmed by the instructions, Univar support, and physical inspection. The valve is Left/Right/Off.

The only question is whether the STC requires a modification to the fuel system; if not, then any fuel selector that is PMA'd for the airframe should be compatible. However, if the STC requires fuel system modification, the new valve must meet the specifications outlined in the STC.

I have no easy way to verify the requirements for complying with the STC installation without the original instructions. I'm 99% certain it's compliant and fine, but I'd like to have something to back it up, just in case it ever becomes an issue.

My Lucas-Emmett STC for my 0-200 (which Randy Thompson now has) does not even mention the fuel selector or fuel system.

I have an old copy of the McKenzie STC for the 0-235 and no mention of fuel selector or fuel system.

Could always call Univair I guess but I'm with John, it's an airframe part. Why Univair had an 'engine eligibility' list I don't know, maybe they didn't know about the other engine STC's.

OK, so it sounds like you're talking about the O200 STC, not a fuel valve STC. What STC was used to install your engine? You can contact the current owner.

I'll bet you dollars to donuts yours doesn't require any changes; why would one but not the other? The O235 will have higher consumption than the O200, anyhow. Not sure why they'd list that and not the O200.

I’m with Dave and John. What Univair has listed is not Approved Data. You need to go by the Cessna IPC or the STC data for your information.
Univair just didn’t know or missed adding the O-200 to the list.
Good luck.

Rick

I haven't verified this, but, I understand the Univair valve is a PMA replacement for the original. (Cessna part numbers with a "U" in front are approved parts made by Univair.) So, if your O200 STC uses the original valve, and since the valve is an airframe component, not an engine component, and your installation conforms to the STC, then the Univair valve is acceptable for your configuration.

In other words, say you had a C85. Say you replaced the valve with the PMA part from Univair. You could then install the O200 using either STC. It is up to the person approving your O200 install to determine that there is no conflict with other modifications, but, installing a PMA part is not even a modification.

Thanks, everyone. I have the Emmett STC (SA547EA) for my O-200, and the STC does not mention the fuel system, so the PMA applies as an airframe part.

Thanks again!
-Ryan