J valves - question

[dbg40]

Christ.........I have GOT to stop reading posts like this!!!!!!!!! I feel like a dinosaur!
I remember thinking it was crazy NOT having a J valve when the K made its apearence, and the SPG! And lets not get into what I thought about those cheezy "single hose contraptions"! Im gonna sit down and have some warm milk now.

 

[morayp]

J valves were in use before pressure gagues. When you had to throw the valve you knew you wre low. Kind of like the "reserve" tank on old VWs.

 

[dbg40]

Here I go again........ If you dove the old doubles enough, you could "feel' the pressure going south on you before the reserve had to be pulled. (c'mon captain, get in here with this!!) There was a little dif. in the pull on the reg, just before it went to reserve, and you knew when to turn before you were told to by just running out of air! Want a real surprise?? forget to keep a constant vigil on the reserve handle, and have it "pre pulled" !!! It's a real learning tool , DON'T FORGET TO CHECK YOUR RESERVE DURING THE DIVE!!

 

[captain]

Here I go again........ If you dove the old doubles enough, you could "feel' the pressure going south on you before the reserve had to be pulled. (c'mon captain, get in here with this!!) There was a little dif. in the pull on the reg, just before it went to reserve, and you knew when to turn before you were told to by just running out of air! Want a real surprise?? forget to keep a constant vigil on the reserve handle, and have it "pre pulled" !!! It's a real learning tool , DON'T FORGET TO CHECK YOUR RESERVE DURING THE DIVE!!

True, the J doesn't just shut off. you start to feel increased inhalation resistance. Some will never completely shut off but it will feel like you are trying to suck a tennis ball through a soda straw. I never found myself without a reserve but I constantly checked the position just like constantly check my SPG.