limit on largest tip size?

But then I read the "Welder's Handbook" by Richard Finch and it says you can't draw more than one-seventh of the acetylene tank's volume per hour, or it might explode! This sounds like it will limit me to a very small tip that would not consume the bottle in less than 7 hours flame-time.

Any thoughts?

"Do not fill acetylene cylinders at a rate greater than 1/7 of their rated capacity, or about 275 cu ft per hour. To prevent drawing off of acetone and consequent impairment of weld quality and damage to the welding equipment, do not draw acetylene from a cylinder at continuous rates in volumes greater than 1/7 of the rated capacity of the cylinder, or 32.1 cu ft per hour. When more than 32.1 cu ft per hour are required, the cylinder manifold system must be used."

"Do not fill acetylene cylinders at a rate greater than 1/7 of their rated capacity, or about 275 cu ft per hour. To prevent drawing off of acetone and consequent impairment of weld quality and damage to the welding equipment, do not draw acetylene from a cylinder at continuous rates in volumes greater than 1/7 of the rated capacity of the cylinder, or 32.1 cu ft per hour. When more than 32.1 cu ft per hour are required, the cylinder manifold system must be used."

If you know the capacity of the bottle and the draw rate of the equipment you have with any given tip..... you can avoid an unsafe condition.

You probably also read that the bottle should be left standing for several hours prior to use if the bottle has been laying in its side.

The gas regulator regulates how fast the gas is with drawn from the cylinder, not the tip size. The tip orifice size determines how many BTU is discharged to the metal.

As long as the acetylene regulator is set for 5psi output then it doesn't matter what orifice size your using as 5psi will supply a very large orifice with-in the drawn down saftey spec's of acetylene as Steve described.

So it does not matter what cu/ft size cylinders you are using as they all will draw acetylene at the same rate.

T_Bone

Tip size DOES equate to the rate that you draw gas out of the cylinder. A larger tip will draw more gas at a given pressure than a small one. That's why the bigger tip generates more BTUs: The more gas you burn, the greater the number of BTUs you generate.

Most welding equipment manufacturers publish charts that tell what the gas flow rate is for a given tip. That's the easiest way to tell if your cylinders are big enough for a particular tip. Running a big tip from a small cylinder is asking for trouble.

There is four items that control flow (cuft/hr) before the tip orifice, one being the mixing chamber, second being the needle vavle on the mixing chamber and third the diameter of the gas supply hose and fourth being the regulator.

If the regulator is set to 5psi output it will be very unlikely that a "B" size act.tank would be overdrawn using standard 3/16" hose with a medmium sized mixing chamber. To test this fact I have used a 60cuft/hr rosebud on a "B" tank at 5psi continious from full to empty without overdrawing the tank flow rate. As far as I know the "B" tank is the smallest refillable acetylene tank available.

If you change anyone of the variables, regulator pressure setting, hose size, mixing chamber size, needle valve or tip orifice will have an effect on tank drawdown.

Since the regulator is first inline from the tank valve, flow can be regulated to stay with-in tank design perimeters by using a low output psi setting of acetylene.

T_Bone

I'm not certain I get your point.

If you're saying that a rosebud tip at 5 psi doesn't draw any more gas than a #000 brazing tip at 5 psi, then I have to disagree.

If you're saying that it's safe to run a 60 cf/hr rosebud off of a 30 cf cylinder, just because you did it once and are still around to talk about it, I still have to disagree.

I'll confess that I sometimes use a rosebud that slightly exceeds the safe drawdown rate for my tank. Just because I haven't blown myself up yet doesn't make it a safe practice and I sure don't recommend it to others.

mark

I'm not making my point clear enough. Here is a quote from Smith welding;

"Every manufacturer publishes recommended pressure settings for every tip, based on the gas consumption of the tip"

Yes the tip orifice can flow "maxmium" gas at the designed flow rate but it's the regulator that regulates the flow to the tip.
Flow can be futher regulated by the needle valve on the mixing chamber.

For example ONLY: DO NOT TRY THIS ON ANY TORCH!
Lets remove the regulator and the mixing chamber from the system. We now have a acetylene tank at 250psi with a 3/16" hose connected to a 30cfh tip orifice. What controls the rate of flow? The tank valve in this example although extreamly crude. Now if the tank valve is fully opened then the tip orifice rate of flow is limiting factor.

Now lets add a regulator to the tank. What controls the rate of flow? The regulator does. As the regulator pressure increases so does the flow rate. With tank valve opened 1/2 turn, barely open the regulator valve to 1/2psi and the rate of flow will be very small thus shown by the low flame size. Open the regulator to 15psi and now the flow is increased as shown by a very large flame size.

Now lets add a mixing chamber. Regulator set to 5psi. What controls the flow? The needle valve. Open the needle valve wide open. What controls the rate of flow? The regulator! I never exceed the safe limits of acetylene. It's just not needed nor do I recomend it.

T_Bone