How to assess thayer valve compression

[Wilco]

My shires thayer valves seem to have a good compression, but how to be sure? Is there a procedure for it? Valves have a big pop when I pull the tuning slides...

[Specialk3700]

Big pop = good compression

[Burgerbob]

Pull a valve slide, wait a few seconds, then press the valve. Still a good pop? The longer, the better.

[Wilco]

Thanks! 2 seconds: good pop. 4 seconds mild pop but still audible. Steady hiss sound after I pull a slide

[Burgerbob]

Sounds pretty OK to me.

[Wilco]

Sounds pretty OK to me.

I checked my xeno bass as well, and there is a strong pop is still there well after 4 seconds. Is that a rotor thing??

[Burgerbob]

They probably just seal better than your Thayers. It's easier for a rotor to do that, much less surface area to deal with.

[MTbassbone]

A tech I went to a while back used a magnehelic gauge to measure the pressure. Not sure if this is correct way or not. I am also not sure what an acceptable reading is either.