These are the self-sealing screws from McMaster-Carr. They have a silicone o-ring built in under the head of the screw. Perfect for this application. The part number is 90825A816 for a package of 10. I bought three packages...enough to do both tanks (plus have a few left over). | |

I was wondering what the relationship between temperature change and pressure change in the tank would be, so I cleared out some of the cobwebs in my brain from college physics. The ideal gas law is: pV=nRT where:
p is the absolute pressure [Pascal] V is the volume [m ^{3}]n is the amount of the substance [mol] R is the ideal gas constant [8.314472 m ^{3}x Pa x K^{-1}x mol^{-1}]T is the absolute temperature [Kelvin]
However, since V, n, and R are (essentially) constants for closed volume leak testing of a fuel tank (i.e. using a manometer), we find that p is proportional to T.
p If we make a few assumptions about starting temperature and pressure, we should be able to come up with a nice conversion between temperature change and water level change. Assumptions: Ambient air temperature is somewhere around room temperature (i.e. 72 degrees F) You use roughly the recommended 1 psi (27.7 inches H _{2}O) for leak testing the tankAmbient air pressure is somewhere around standard pressure (i.e. 29.92 inches Hg)
Plugging all this in results in a conversion that
Damn I'm such a nerd. :-( | |

Well, with all that figured out, I got down to testing the right tank. Here's the water level and temperature at the start of the test... | |

...and after a few hours. The change in water level is quite close to what would be expected for the indicated change in temperature. Right tank certified leak free! | |

I was feeling pretty cocky as I set the right tank aside, hooked up the left tank and
started pumping it up. But what the frack was going on?!? I couldn't get the
water level to even | |

Anyway, here's the water level and temp at the start of the test... | |

...and a few hours after. Again, the change in water level is right in-line with what would be expected for the temperature change. Left tank certified leak free! |