or this site…
This makes sense now. Thank you.
I can only go to 20psi, cause I am using a 20lb tank…So at 20psi, I think I will pour beer out of it in 2 days, and keep trying it until the desired carbonation is reached.
The size of the tank has nothing to do with how high you can set your secondary regulator. If your secondary regulator only goes to 20 psi, then that’s as high as you can go. If your secondary reads to 30 or 60 psi as many of them do, but you can only get 20 psi out of the tank, then your tank is probably almost empty. What does the primary regulator say?
CO2 tanks have liquid in them when they are full, and maintain a fairly constant pressure inside the tank as long as the liquid is there. The pressure they have depends on the temperature of the tank. PV=nRT R is a constant. In the tank, volume (V) is mostly constant, but a you use the gas the V will increase over time as the liquid turns to gas. n is the amount of gas, which will increase slightly as the volume increases. The temperature you keep the tank can vary, so this will affect the pressure of the gas in the tank slightly, but as the pressure increases the gas is more likely to turn into liquid. So anyway, the bottom line is that as long as there is liquid in the tank the reading on the primary, high-pressure, gauge will remain pretty much where it started. It is only when the tank is empty of liquid that the needle on that gauge starts to move.
Yes, you can turn up the pressure and carbonate it faster, but like svejk said, you have to catch it at the right point. Over-carbonated beers are a total pain to deal with, so I don’t recommend turning it up that way. Your choice though . . .
If you’re in a hurry, the better way to do it in my opinion is to set it to the pressure you intend to serve with, then shake the keg vigorously and repeatedly for as long as you can take it. Take a break and then do it some more. It takes some energy and you’ll probably work up a sweat, but there’s no danger of over-carbonating with this method. And it can be a good workout. 
The shake method works really well if you leave a little extra head space and have a strong back.
Another is to connect the keg once or twice everyday for a week and pressure it back up to 40 psi. This works fairly well, but the amount of headspace plays a role. More headspace= more co2.
You should be able to adjust the regulator to 40 psi.
My primary goes up to like 60psi, but I turn the screw down all the way and the most I can get out of the tank is 20psi, but the other guage says my 20lbs tank is at 600psi. I’m not sure why I can’t get it to pressurize anymore.
When I go into work today, I’ll take a look at what the gauge says and post more.
Check to see if there is a nut that is preventing you from moving the screw in further. If you move where the nut is located on the screw you should be able to screw it in further and get more psi out of it. Although I still think that’s the wrong way to do it
Ya I loosened that nut, and put the screw down further…but to no avail, still maxed out at 20psi.
If you can screw it all of the way in and it still maxes out at 20 psi, something is wrong with it. I don’t know enough off the top of my head about the internal workings of regulators to know what though.