P337 Rear vacuum pressure relief valve
 

Hello; I have a 1979 P337 and just had a new vacuum pump installed on the rear engine. However the suction is reading only about 3 versus around 4.8. Somebody (Cessna?) has hidden the relief valve somewhere that my mechanic and I can't find. Does anyone know where the rear suction relief valve is on a Pressurized 337 is located?
Thanks

Open the gear doors. You can access it through the left gear leg door

Thank You Kim, looks like we just found it just forward of the firewall inside under the floor board. Of course we had to take a panel off the pressure vessel. I have the gear door removal STC as well. Can you get to it that way as well?

you should have the long leg doors. If you open the gear doors it should be inside the left one.

Thank You; Much easier and smarter than the interior panel

Vacuum relief valves
 

Just wanted to add on here. The pump relief valves, there are two, one for each engine. On my 1976 the front is on the firewall on the copilot side in the engine compartment. The rear is in the wheel well of the pilots side maim gear. There are tabs on the adjusting wheel that are used to limit the movement of the adjustment wheel.

the rear adjustment in mine was blind. And to see the result you need to start the engine read the gauge and then determine the effect. I was doing this to allow for the lower vacuum requirements once removing all of the gyros.

Hope this helps