School me on PSI please?

[JJinMD]

My Anvil bucket sometimes doesn't seal great, so I put a 10lb. weight plate on it. Recently, I had mistakenly used a gas ball lock fitting with an integrated check valve on the fermenter to get "free" CO2 to purge serving kegs. When I went to correct this issue, I realized there was a good amount of pressure in the fermenter. So my question is, because I had put a 10lb. weight on the lid, does that mean it was at 10 PSI? I am thinking not because I am not including the "per inch" in a calculation, but not really sure? What is the correct answer, is it possible to determine a rough idea?

 

[Dland]

I'm pretty sure you'd need a gauge to measure PSI. The fact that it is a 10# weight is not measure of internal pressure.

 

[PCABrewing]

When I went to correct this issue, I realized there was a good amount of pressure in the fermenter. So my question is, because I had put a 10lb. weight on the lid, does that mean it was at 10 PSI? I am thinking not because I am not including the "per inch" in a calculation, but not really sure? What is the correct answer, is it possible to determine a rough idea?

The short answer is no.

There is not enough information provided to determine how many PSI was in the fermenter.
What is the diameter of the lid?
Is the weight the only thing holding it in place?

10 PSI in the fermenter with a 12" diameter lid would equate to ~113lb of force on the lid

As Dland says a guage is the best way to determine the current PSI. Using weight in the calculation would only tell you the max pressure when it lifted, which may be undetectable in action. That's basically how a regulator works.

 

[IslandLizard]

Without including the force of the clasps, if your lid is 30 square inches, you effectively would have had only 0.33 psi in the fermenter headspace.

But the 10# weight may have helped sealing the lid, flattening it out over the rim and make a better seal. That helped the clasps to keep the lid shut. Adding the force of the clasps, pressure may have been quite a bit higher, yes.

 

[JJinMD]

Thanks, I figured it wasn't so simple, just thought there might be a way to figure it out but I hadn't really thought about the clasps being part of the calculation. I kept thinking about how my pressure cooker can get up to 15 psi with just a "rattler" weight on top that is nothing but a few ounces, which I guess is just a matter of calibration with gauges.

 

[IslandLizard]

up to 15 psi with just a "rattler" weight on top that is nothing but a few ounces,

Because... the stub in the lid the "pressure weight" is placed onto has only a 1/8-3/16" diameter opening.

A 1/8" diameter opening is 0.0123 sq.in.
To hold that closed at 15psi, you'd need 15psi * 0.0123 sq.in = 0.18 lb = 2.94 oz weight.

 

[JJinMD]

Because... the stub in the lid the "pressure weight" is placed onto has only a 1/8-3/16" diameter opening.

A 1/8" diameter opening is 0.0123 sq.in.
To hold that closed at 15psi, you'd need 15psi * 0.0123 sq.in = 0.18 lb = 2.94 oz weight.

Interesting! Thank you. This is all making much more sense to me now.