Check whether one acetylene cylinder can feed your torch tip. Enter the cylinder contents, choose the withdrawal rule, and enter the tip’s flow; the page returns the hourly limit, how many cylinders to manifold, and the flame time.
Use this before running a large heating tip, a cutting tip on heavy plate, or a manifold of cylinders, when you need to know whether the acetylene draw stays within the cylinder’s limit.
Read the cylinder’s acetylene capacity in cubic feet from its label or the supplier’s paperwork, and the tip’s acetylene flow in cubic feet per hour from the tip chart. If the cylinder is partly used, enter the percent remaining; the limit is based on the gas actually in it.
Acetylene is dissolved in acetone inside the cylinder. Drawing too fast pulls acetone out with the gas, which damages regulators and hoses and changes the flame.
Industry guidance limits acetylene withdrawal to a fraction of the cylinder’s contents per hour. The long-standing figure is one-seventh per hour; Compressed Gas Association guidance also cites one-tenth per hour for intermittent use where solvent carry-over matters, and one-fifteenth for permanent installations. Pick the rule that applies to your work.
If the torch demand is larger than one cylinder’s limit, cylinders are manifolded so the draw is shared. The number needed is the demand divided by one cylinder’s limit, rounded up. Flame time is total contents divided by demand.
contents = capacity × % remaining
max draw per cylinder = contents / rule (7, 10, or 15)
cylinders = ceil( demand / max draw )
flame hours ≈ cylinders × contents / demand
Each row below starts from the default inputs and changes only the columns shown. Recompute any row by hand with the formula above.
| Capacity | Remaining % | Rule | Demand | Max CFH | Cylinders | Hours |
|---|---|---|---|---|---|---|
| 145 | 100 | 1/7 | 20 | 20.7 | 1 | 7.3 |
| 145 | 100 | 1/10 | 20 | 14.5 | 2 | 14.5 |
| 300 | 100 | 1/7 | 20 | 42.9 | 1 | 15.0 |
| 390 | 100 | 1/10 | 80 | 39.0 | 3 | 14.6 |
| 145 | 50 | 1/7 | 20 | 10.4 | 2 | 7.3 |
| 40 | 100 | 1/7 | 10 | 5.7 | 2 | 8.0 |
With the calculator defaults (Cylinder capacity (cu ft) = 145; Contents remaining (%) = 100; Withdrawal rule = 1/7; Torch acetylene demand (CFH) = 20), the arithmetic runs like this:
contents = capacity × remaining = 145 × 100% = 145 cu ft
limit = contents / 7 = 20.71 CFH
cylinders = ceil(demand / limit) = ceil(20 / 20.71) = 1
flame hours ≈ cylinders × contents / demand = 1 × 145 / 20 = 7.25 h
Result: 20.7 CFH max per cylinder. One cylinder covers 20 CFH under the 1/7 rule. At 20 CFH, the cylinder give about 7.3 h of flame time.
Now change Withdrawal rule to 1/10 and leave everything else alone:
contents = capacity × remaining = 145 × 100% = 145 cu ft
limit = contents / 10 = 14.50 CFH
cylinders = ceil(demand / limit) = ceil(20 / 14.50) = 2
flame hours ≈ cylinders × contents / demand = 2 × 145 / 20 = 14.50 h
Result: 14.5 CFH max per cylinder. A 20 CFH demand needs 2 cylinders manifolded under the 1/10 rule. At 20 CFH, 2 cylinders give about 14.5 h of flame time.
Moving from the 1/7 rule to the 1/10 rule lowers this cylinder’s limit from about 20.7 to 14.5 CFH, so the same 20 CFH tip now needs two cylinders on a manifold. Heating tips are where this bites.
Large heating tips are the usual problem: their acetylene flow can be several times what a small cutting tip uses. Look up the actual flow for your tip size and pressure before you light it, and compare it with the limit here.
As a cylinder empties, its limit drops with its contents. A cylinder that runs fine at the start of the day can start spitting acetone in the afternoon. Enter a lower percent remaining to see the reduced limit.
Keep acetylene cylinders upright, and if one has been laid down, stand it up and let it settle before use as the supplier directs. Do not use acetylene above 15 psig.
Units: Cubic feet for contents, cubic feet per hour for flow, hours for flame time.
Where the model stops: It applies a fixed fraction per hour. It does not model temperature, which changes how readily the acetone releases gas, or regulator and hose capacity.
Not a substitute: Follow your gas supplier’s guidance, CGA and OSHA requirements, and the torch maker’s tip charts.
One-seventh per hour is the widely quoted general figure. If your supplier, site, or application calls for one-tenth (intermittent use where acetone carry-over matters) or one-fifteenth (permanent installations), use that. When unsure, the lower draw is the conservative choice.
The acetylene is dissolved in acetone throughout the cylinder, and how fast it can come out depends on how much is dissolved. A half-empty cylinder has half the limit.
Acetone is drawn out with the gas. It can damage regulator seats and hoses, and the flame becomes purplish and less efficient.
Alternative fuel gases do not have the same withdrawal limit, but they need their own tips and have different flame characteristics. That is a separate decision.