Auto Drain Filter Operation

[bfr57]

I'm looking at getting one of these auto drain inline filters:

https://www.amazon.com/dp/B005JDL5RU/?tag=atomicindus08-20

I can't seem to find any info on how the auto draining function works. Does it drain once it gets to a certain level no matter what the pressure is? Or, does it only drain if pressure is removed, thus opening the drain?
I really don't want to let the pressure off my system just to let this drain.

 

[engineer2]

All the ones I've seen have a simple float valve.
The float valve tends to stick or leak after a while, so annual maintenance is required.