"Anytime you up the pressure, it's got more push and will move more gas through the torch, regarless of needle settings."
When you increase the pressure at the regulator, you increase the amount of gas available to your torch. Your needle valves are what regulate how much gas actually gets to the torch from the lines. I'll use oxygen pressure (from a tank) as an example - it works the same for fuel, as well. The numbers are just for demonstration purposes. Say you have 20 psi coming out of the oxygen tank and through the line (this is what Bethlehem recommends for the high end pressure), once it hits a closed valve, it stops and no oxygen is getting through the torch. If you crack open the valve (say 1/16 of a turn for example), you are only getting so much of the oxygen through to the torch. If you open the valve all the way, you are getting all of the recommended oxygen to the torch and can get everything out of that torch. When you have higher pressure in the line, you turn the valve in smaller increments to increase or decrease the amount of oxygen coming into the torch. Your control is touchier, but you have a broader range. You can go from completely closed getting no oxygen to completely open getting as much oxygen as the manufacturer recommends - the full 20 psi - and everything in between.
Now, say you set the pressure to 10 psi. When the needle valve is closed, there is no oxygen getting to your torch. When it is cracked open (say that 1/16 of a turn used as an example), there is some oxygen getting through to the torch, but only 1/2 as much as if you were running 20 psi. If you were to open the valve all the way, you would only get as much oxygen as the regulator alllows, and in this example that would be 10 psi, or half of what the manufacturer says you need to get everything out of that torch. You will have to turn your valve in larger increments to increase or decrease the amount of oxygen coming to the torch. Basically, you would have to turn the valve 1/8 of a turn at a regulator setting of 10 psi to get as much oxygen as turning it 1/16 of a turn at a regulator setting of 20 psi. Your control is less touchy, but you have a narrower range. You can go from completely closed getting no oxygen to completely open getting only half the oxygen as the manufacturer recommends at 10 psi and everything in between, but nothing more.
Some people like touchy controls. Some people don't. Some people like them for some applications, but not for others. This is where personal preferrance comes in. But, the fact remains that the needle valves do control how much of the gas from the lines gets through the torch. The regulator pressure only dictates the upper limit.
PS There are days that I switch from working soft glass to working boro. I work with my pressure set to the highest recommended setting when I'm on a tank. I just turn my valve knobs up more to push more oxygen and propane through my torch. I don't ever get up to change the regulator settings.
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