What are the 3 vents / weights on this Chinese pressure canner?

1. Which valve is which?

   See labels below:

2. When to use the auto valve?

   According to user manual Page 6, Section 5.7, you are supposed to move the handle on the auto valve at least twice a week to make sure it doesn't get stuck. Other than that, just leave it alone and let it do its thing. It will automatically maintain your pressure and temperature. I guess the auto valve is a calibrated device and they don't want you to touch it too often which would wear out the spring, so they give you the manual valve for routine pressure release.

   Additionally, if you see pressure rises to 0.175MPa but no steam comes out of the auto valve, then it's considered a malfunction and you should have the auto valve checked and repaired(5.6, Page 6).

3. When to use the manual valve?

   Page 4, Section 4.3 and 4.4 says you are supposed to bend the tube down and slide it into the slot on the pot. And you should let the manual valve open until 1 minute after steam comes out of it, to purge the air. This is why you can not use the auto valve for this job: it doesn't have the tube so can not efficiently purge air from the bottom of the pot.

   Page 5, Section 4.7 recommends you don't open the manual valve until 2 minutes after pressure fully drops to avoid shooting hot water out of it. Also, rapid change in pressure and temperature can cause damage to the contents in the pot. However, if you don't want to wait, you can release the pressure immediately after cutting the power, just be careful(4.6, Page 5).

4. When to use the safety valve?

   The manual didn't mention anything except you should have it checked every 6 months. So just leave it alone and hope you never have to activate it.

(This thing is actually a medical sterilizer. As is any electric medical devices the user manual actually includes a full EMC test standards(GB/T 17626) and results).

Not a full answer, but I found the video on this page showing how to use a very similar device (no sound that I can see, and text in Chinese) on Alibaba.

It seems that the two valves with sort of rocker style heads are for steam release - you can flip these to release pressure once sterilization is complete - a spoon or fork or something similar will probably work, but it looks like some sort of tool in the video.

I suspect that the front one with what look like nuts is probably so that you can adjust the pressure and hence temperature of sterilization. I don't think the pressure gauge needs much explanation.

My only guess with respect to the hose is that it is intended to get the pressure or temperature at the point of sterilization - this is critical for medical applications; if you underestimate the temperature and your things aren't sterile, it leads to all sorts of trouble.