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newSchoolWorks.com › VoTechWorks › Building & Construction › Welding › Oxy-fuel & Plasma Cutting › Lesson 2
BLD-WELD01-09 · Lesson 2 · 12 clock hours · demo

Oxy-fuel Equipment Setup, Gas Pressures, and Leak Testing

Objective. Students assemble an oxy-fuel cutting outfit, set working pressures from a manufacturer cutting chart, and verify a leak-free system using approved soapy-water method before ignition.

Why Setup Order Matters

Oxy-fuel cutting joins oxygen and a fuel gas—almost always acetylene in building and construction work—to produce a flame hot enough to cut structural steel. Both gases are stored under high pressure and are potentially dangerous if handled carelessly. A disciplined, step-by-step setup sequence is not a formality; it is the primary defense against fires, flashbacks, and cylinder explosions. Every step in the sequence exists because something bad happened when it was skipped. Follow the order every time, without shortcuts.

Personal Protective Equipment Before You Touch Anything

Before approaching the cylinder station, put on your PPE:

Step-by-Step Equipment Setup

Step 1 – Inspect cylinders and components.

Check that oxygen and acetylene cylinders are secured upright in a cart or to a wall. Inspect hoses, regulators, and the cutting torch for cracks, oil contamination, or damaged threads. Never use equipment that shows damage. Oxygen and oil contact is a serious fire and explosion hazard—keep all fittings oil-free.

Step 2 – Crack each cylinder valve.

Point the valve opening away from people. Open each cylinder valve briefly (one-quarter turn) and close it immediately. This clears dust or debris from the valve seat before the regulator is attached. Do this one cylinder at a time.

Step 3 – Attach regulators.

Oxygen regulators use a right-hand thread; acetylene regulators use a left-hand thread (the fitting nut has a notch or groove as a reminder). Start each connection hand-tight, then snug with an open-end wrench. Do not over-torque—brass fittings damage easily.

Step 4 – Connect hoses.

Oxygen hose is green (right-hand thread); acetylene hose is red (left-hand thread). Attach each hose to its matching regulator outlet and to the torch inlets. Hand-tight, then wrench-snug.

Step 5 – Install the cutting tip.

Select the tip size specified in the manufacturer's cutting-tip chart for the material thickness you will cut. Seat it fully and tighten with the correct wrench—do not use pliers, which can round the nut and create a leak path.

Step 6 – Back out regulator adjusting screws.

Before opening cylinder valves fully, turn the adjusting screw on each regulator counterclockwise until it turns freely. This ensures no delivery pressure is applied when you open the cylinder.

Step 7 – Open cylinder valves and set delivery pressures.

For oxygen: open the valve fully (standing to the side, never in front of the gauge face). For acetylene: open no more than one full turn—the cylinder valve must stay reachable for emergency shutoff, and acetylene becomes unstable at pressures above 15 psi.

With torch valves closed, slowly turn in (clockwise) each regulator adjusting screw until the delivery gauge reads the pressure shown in the manufacturer chart for your tip size and material thickness. Typical charts list separate working pressures for oxygen and acetylene; follow them exactly.

Step 8 – Purge hoses one gas at a time.

Open the oxygen torch valve briefly to purge the oxygen hose, then close it. Repeat with the acetylene torch valve. Purging removes air or cross-contamination from the hose before ignition. Never purge both valves open at the same time.

Reading the Cutting-Tip Chart

Manufacturers publish cutting-tip charts that list, for each tip size, the recommended oxygen pressure, acetylene pressure, and the range of steel thickness that tip handles. Always use the chart for your specific torch brand—values differ between manufacturers. Pressures are given in psig (pounds per square inch gauge). Set your regulator delivery pressure to match the chart value for the thickness you plan to cut; operating outside the recommended range produces a poor cut and increases hazard.

Leak Testing—Zero Bubbles Before Ignition

After pressures are set, test every threaded connection for leaks before any ignition attempt. Use a commercial leak-test solution or plain soapy water applied with a brush or squeeze bottle. Never use an open flame to find a gas leak.

1. Apply solution to all regulator inlet and outlet connections, hose-to-regulator connections, hose-to-torch connections, and the tip seat.

2. Watch for bubbles. Even slow, small bubbles indicate a leak.

3. If bubbles appear, close both cylinder valves, release system pressure through the torch valves, tighten or replace the leaking fitting, re-pressurize, and re-test.

4. Proceed only when zero bubbles appear at every connection. The instructor must sign off on the leak-test result before ignition.

Never attempt to tighten a fitting while the system is pressurized beyond the purge step described above.

Acetylene Pressure Limit—A Hard Rule

Acetylene becomes chemically unstable at gauge pressures above 15 psi. This is not a guideline—it is a fundamental property of the gas. Regulators and cutting-tip charts are designed to keep working pressures well below this limit. If you ever see an acetylene delivery gauge reading above 15 psi, shut the system down and report it immediately.

Key terms8

Cracking a cylinder valveBriefly opening and closing a cylinder valve before attaching a regulator, to blow dust or debris off the valve seat.
Regulator adjusting screwThe threaded knob on a pressure regulator that controls delivery (working) pressure; backed out (counterclockwise) before cylinder valves are opened.
Delivery pressure (working pressure)The downstream gas pressure set by the regulator and delivered to the torch, measured in psig; must match the manufacturer cutting-tip chart for the tip size and material thickness in use.
Left-hand threadA thread that tightens by turning counterclockwise, used on acetylene fittings as a safety feature to prevent accidental interchange with oxygen fittings.
Purging hosesBriefly opening one torch valve at a time to flush air or contaminants from the hose before ignition; done one gas at a time with the other valve closed.
15 psi acetylene limitThe maximum safe gauge pressure for acetylene; above this pressure the gas can become chemically unstable and potentially detonate without warning.
Cutting-tip chartThe manufacturer's published table listing the correct tip size, oxygen pressure, and acetylene pressure for a given range of steel thicknesses.
Soapy-water leak testAn approved method of checking pressurized gas connections for leaks by applying leak-test solution or soapy water and observing for bubbles; no open flame is ever used.

Worked examples4

1. The cutting-tip chart for a No. 1 tip states an oxygen working pressure of 30 psi and an acetylene working pressure of 5 psi. After setting pressures, you read 27 psi on the oxygen gauge and 5 psi on the acetylene gauge. Is the oxygen pressure within the ±2 psi tolerance required by the checklist?
  1. Chart value for oxygen: 30 psi.
  2. Allowable range: 30 − 2 = 28 psi (low limit); 30 + 2 = 32 psi (high limit).
  3. Gauge reads 27 psi. Compare: 27 < 28.
  4. 27 psi falls below the lower limit of 28 psi.
Answer: No. 27 psi is 3 psi below the chart value, which exceeds the ±2 psi tolerance. Turn the oxygen regulator adjusting screw clockwise until the gauge reads between 28 and 32 psi, targeting 30 psi.
2. A cutting-tip chart lists acetylene working pressure as 8 psi for a No. 2 tip cutting 1-inch steel. A student sets the acetylene delivery gauge to 16 psi to 'get more heat.' Is this acceptable, and why?
  1. Identify the acetylene pressure limit: acetylene is chemically unstable above 15 psi gauge pressure.
  2. The student set the gauge to 16 psi, which exceeds 15 psi.
  3. Additionally, 16 psi is double the chart value of 8 psi, far outside the ±2 psi tolerance.
  4. Both the safety limit and the chart tolerance are violated.
Answer: Not acceptable. 16 psi exceeds the 15 psi maximum safe acetylene working pressure and is well outside the chart specification. The system must be shut down, pressure bled off, and the regulator reset to 8 psi before work continues.
3. You are setting up for a cut requiring an oxygen delivery pressure of 40 psi. What is the minimum and maximum gauge reading that falls within the ±2 psi checklist tolerance?
  1. Target pressure from chart: 40 psi.
  2. Lower limit: 40 − 2 = 38 psi.
  3. Upper limit: 40 + 2 = 42 psi.
  4. Acceptable range: 38 psi to 42 psi, inclusive.
Answer: The oxygen delivery gauge must read between 38 psi and 42 psi to pass the checklist. Any reading outside this range requires regulator adjustment before proceeding.
4. During leak testing, a student applies soapy water to six connections and finds slow bubbles at one hose-to-regulator fitting. List the correct corrective sequence.
  1. Step 1 – Close both cylinder valves immediately.
  2. Step 2 – Open torch valves one at a time to bleed residual pressure from both hoses until both delivery gauges read zero.
  3. Step 3 – Close torch valves.
  4. Step 4 – Tighten or replace the leaking hose-to-regulator fitting.
  5. Step 5 – Re-open cylinder valves and reset delivery pressures per the cutting-tip chart.
  6. Step 6 – Re-apply soapy water to all connections, including the one just tightened.
  7. Step 7 – Confirm zero bubbles at every connection before calling the instructor for sign-off.
Answer: Shut down the system, bleed pressure, fix the fitting, re-pressurize, and re-test all connections. Proceed only after zero bubbles appear at every joint and the instructor signs off.
In class: Instructor demonstrates full setup sequence: cracking cylinder valves, attaching regulators hand-tight then wrench-snug, purging hoses one gas at a time, attaching the cutting torch and tip, setting regulator delivery pressures per the chart for a given tip and material thickness. · Students rotate in pairs through four stations to repeat the setup procedure; instructor observes each pair and annotates a setup checklist in real time. · Each pair applies soapy water (no open flame) to every fitting, identifies any leak source, tightens or replaces the fitting, and re-tests; instructor signs off when zero bubbles appear.
Materials: Oxy-acetylene outfit (cylinders, dual regulators, hoses, torch, cutting tips sizes 0–3), manufacturer cutting-tip chart, leak-test solution, open-end wrenches, setup checklist, PPE (shade 5 goggles, leather gloves, leather jacket).
Check: Instructor checklist: all eight setup steps completed in correct order, pressures within ±2 psi of chart value, zero leaks confirmed before sign-off; any safety step skipped restarts the entire sequence—pass requires 100% checklist completion.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Safety and setup procedures
1. Which action is performed immediately before attaching a regulator to a cylinder valve?
Oxy-fuel safety—fuel gas properties
2. What is the maximum safe acetylene working pressure at the regulator delivery gauge?
Equipment identification and setup
3. How are acetylene fittings distinguished from oxygen fittings to prevent accidental interchange?
Oxy-fuel safety—ignition and purging
4. During hose purging, why must the operator open only one torch valve at a time?
Pressure setting and cutting-tip chart reading
5. A No. 2 cutting tip chart specifies an oxygen working pressure of 35 psi. Which gauge reading passes the ±2 psi checklist tolerance?
Leak testing and equipment inspection
6. What approved method is used to locate gas leaks in a pressurized oxy-fuel system?
Leak testing and corrective action
7. A student finds bubbles at a hose-to-torch fitting during leak testing. What is the correct next step?
PPE selection—oxy-fuel operations
8. Which PPE item is specifically required to protect the eyes during oxy-fuel cutting operations?
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