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Originally Posted by kbinkster
I'll try to explain it with an analogy.
Say you have a water spigot at your house. The water pressure is regulated and set to 40 psi. When you turn open the spigot a little, you get a trickle of water.
The water company comes along and increases the water pressure to 80 psi. When you go to crack open the spigot, you do not have to turn it very much for the trickle of water to start coming out. That trickle of water is still just dribbling out the same as it was before. The water is not shooting out of it any faster than it was at the lower pressure.
Next, the water company comes along and turns the water pressure down to 20 psi. You have to open the spigot more than normal to get the trickle of water. The trickle is still trickling. It isn't moving in slow motion or anything. You just had to turn the valve more to get it to come out like it did before. Now, if you open the spigot valve all the way, you might feel frustrated because there just isn't enough water coming out. The low water pressure limited how much water could get to the spigot.
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The water at the higher pressure is coming out faster. There is an increase in velocity through the reduction point. This is increased by the amount of pressure behind the reduction point. The only reason water will run out as slow as the first trickle in your annalogy, is because it's hitting metal before it comes out. If it didn't hit metal and slow down, it would squirt very far and fast... much farther and faster than the 40 PSI line. This is the way a pressure washer works. Sorry Kimberly, but pressure in the line has everything to do with how fast the gas moves out of your torch face. It creates the woosh sound you hear at higher pressures. To say it doesn't make a difference, by comparing it to a sink experiment is just plain silly. Read some stuff on Physics and stop playing with the hose.
