Oxyfuel Cutting Applications 282

"Oxyfuel Cutting Applications" provides an overview of the oxyfuel cutting process, its equipment, operating procedures, and safety requirements. Before performing oxyfuel cutting, it is important to correctly setup the oxyfuel outfit and perform essential safety inspections. During the cutting process, an operator must control specific variables, including cutting tip height, gas flow rate, travel speed, and torch angles. Understanding these variables and the proper cutting procedures helps produce a quality oxyfuel cut.

The information in this class helps prepare users to perform oxyfuel cutting, a popular thermal cutting process with a variety of applications. After taking this class, users will be familiar with many of the considerations and variables that oxyfuel cutting involves, which are essential for safely and successfully producing quality cuts.

Class Details

Class Name:
Oxyfuel Cutting Applications 282
Difficulty:
Intermediate
Number of Lessons:
24

Class Outline

  • Oxyfuel Cutting
  • Oxyfuel Flames
  • Oxyfuel Gas Cylinders
  • Gas Regulators
  • Gas Hoses and Safety Devices
  • Gas Equipment Maintenance
  • Gas Equipment Safety
  • Review: OFC and Gas Equipment
  • Oxyfuel Torch Components
  • Torch Types
  • Torch Maintenance
  • Torch Malfunctions
  • Review: OFC Torches
  • OFC Setup
  • Preparing to Light the Torch
  • Lighting the Torch
  • Preheating and Starting the Cut
  • Maintaining the Cut
  • Shutting Down Equipment
  • Review: OFC Process Steps
  • OFC Variables and Quality
  • Advantages and Limitations of Oxyfuel Cutting
  • Personal Protective Equipment for OFC
  • Final Review

Objectives

  • Describe oxyfuel cutting.
  • Identify neutral, oxidizing, and carburizing flames.
  • Describe oxygen and acetylene cylinders.
  • Describe the gas regulators and hoses used in oxyfuel cutting.
  • Describe maintenance practices for oxyfuel cutting gas equipment.
  • Describe safe handling and storage practices for oxyfuel cutting gas equipment.
  • Describe the components of an oxyfuel cutting torch.
  • Distinguish between positive-pressure and injector cutting torches.
  • Describe maintenance practices for oxyfuel cutting torches.
  • Distinguish between backfire, sustained backfire, and flashback.
  • Describe setup procedures for oxyfuel cutting equipment.
  • Describe the steps necessary to safely light an oxyfuel cutting torch.
  • Explain how to preheat and initiate an oxyfuel cut.
  • Describe variables the operator must control while making an oxyfuel cut.
  • Describe the steps necessary for shutting down oxyfuel cutting equipment.
  • Describe how process variables affect the quality of oxyfuel cuts.
  • Identify the advantages and limitations of oxyfuel cutting.
  • Describe personal protective equipment used in oxyfuel cutting.

Job Roles

Certifications

Glossary

Vocabulary Term Definition
acetone A flammable liquid used in acetylene cylinders to dissolve and store acetylene. Acetone allows for safer storage of acetylene.
acetylene A colorless, flammable gas that is one of the most common fuel gases used in oxyfuel cutting. Acetylene should not be used at pressures above 15 psi (103.4 kPa) because it becomes highly unstable at higher pressures.
adjusting screw A component in a gas regulator that controls the gas flow from the cylinder into the regulator and prevents any damage to the regulator's components. Adjusting screws must be released prior to opening the cylinder valve.
alloy steel A steel that contains intentionally added materials that change the properties of the metal. Alloy steels commonly include elements such as chromium, manganese, molybdenum, and nickel.
backfire A torch malfunction that occurs when the flame moves up into the tip of the torch temporarily. Backfire is fairly common and is not a major safety concern.
backflow The unwanted movement of gas in the direction opposite the intended flow. Backflow of oxyfuel gases can be prevented by check valves.
ball valve A valve that uses a rotating spherical obstruction to control the flow of gas. Ball valves can be adjusted to a range of positions between fully closed and fully open.
bell-mouthed orifices A hole that has a flared opening and is not a perfect circle. Bell-mouthed orifices on oxyfuel cutting tips affect the shape and direction of the preheat and cutting jet flames.
beveled Set at a sloping angle. Beveled edges are an indication of a quality oxyfuel cut.
brass A nonferrous alloy containing copper and zinc. Brass has high tensile strength and corrosion resistance.
brazing A process that joins two base metals by melting a filler metal at a temperature above 840°F (449°C) but below the melting point of the base metals. Brazing differs from welding because only the filler metal is melted.
carbon A common nonmetallic element found in all types of steel. Carburizing flames can add extra unwanted carbon to a workpiece's heat-affected zone.
carburizes Chemically absorbs or adds carbon to a material. In oxyfuel cutting, a flame with more fuel gas than oxygen carburizes the metal workpiece.
carburizing flame A type of oxyfuel flame that contains more fuel gas than oxygen. Carburizing flames burn at lower temperatures than neutral and oxidizing flames.
cast iron An alloy of iron, carbon, and silicon that contains at least 2.0% carbon. Cast iron offers heat resistance and compressive strength.
check valves A directional control valve that allows fluid to flow in only one direction. Check valves are installed between the gas hoses and the torch and/or between the gas hoses and gas cylinders to prevent the unintentional backflow of gases.
chromium A hard, shiny, steel-gray metal that is often used as an alloying element. Chromium improves the hardenability and corrosion resistance of steel.
combustible Capable of catching fire and burning. Combustible materials must never be present in a thermal cutting or welding area.
concave Curving inward, like the interior of a bowl. Concave surfaces on an oxyfuel cut typically result from travel speeds that are too high.
copper A reddish-brown metal that is very ductile, thermally and electrically conductive, and corrosion resistant. Copper is often used to make cutting and welding tips for oxyfuel torches.
cut face The exposed surface of a cut. Cut faces may exhibit deep drag lines, pressure marks, or pitting if improper cutting variables are used during oxyfuel cutting.
cutting jet A concentrated, high-powered stream of pure oxygen used to pierce and cut metal during oxyfuel cutting. Operators use the cutting jet lever on the torch to control the cutting jet.
cutting jet lever The lever on an oxyfuel cutting torch that controls the release of the cutting jet flame. Pressing the cutting jet lever releases the high-powered, concentrated stream of oxygen that oxidizes and severs ferrous metal.
cutting tip A replaceable nozzle on an oxyfuel cutting torch through which gases escape. Cutting tips are made in a variety of sizes and orifice configurations for use with different fuel gases.
cutting tip height The distance between an oxyfuel torch's cutting tip and the workpiece surface. Cutting tip height affects cut quality.
cylinder cap A device used to protect the valve mechanisms of a gas cylinder from physical damage while the cylinder is in storage or transport. Cylinder caps must be kept on the gas cylinders when the cylinders are not secured.
cylinder pressure The pressure under which gas is stored within its cylinder. Cylinder pressure is far too great to be suitable for welding or cutting processes and must be reduced to a lower working pressure.
cylinder truck A two-wheeled dolly used to safely secure gas cylinders while in use. Cylinder trucks can also be used to safely transport gas cylinders between locations.
cylinder valve A device that opens, closes, or obstructs an opening or passageway to control the flow of gas from a gas cylinder. Cylinder valves are made of forged brass and designed to withstand high pressures.
cylinder-pressure gauge The device that indicates the pressure of gas present in the gas cylinder. Cylinder-pressure gauges are marked with a graduated scale that is specific to the type of gas in the cylinder.
diameters The distance from one edge of a circular or cylindrical object to the opposite edge, as measured through the center. The diameter of an oxyfuel cutting tip's center orifice determines the size of the cutting tip.
double-stage regulator A type of regulator that adjusts the cylinder pressure to the required working pressure in two steps. Double-stage regulators maintain a constant delivery pressure better than single-stage regulators, although the cylinder pressure may vary.
drag angle A travel angle that points the torch tip opposite the direction of cutting. Drag angles can be used when performing oxyfuel cutting on alloy steels and cast irons.
drag lines A mark left on the face of a cut after a thermal cutting operation. Drag lines indicate various cutting variables, such as cutting direction, speed, and angle.
dross Hardened molten metal that accumulates on a workpiece undergoing oxyfuel cutting operations. Large amounts of dross can accumulate on a workpiece's underside if excessively slow travel speeds are used.
earmuffs Protective earwear that prevents hearing damage and protects the outer ear from flying sparks or debris. Earmuffs consist of two ear coverings connected by a band.
earplugs A protective device that is inserted in the ear to block noise. Earplugs protect against hearing loss.
equal-pressure torches A type of oxyfuel torch that requires equal pressures of oxygen and fuel gas to ensure the gases reach the mixing chamber simultaneously and mix properly. Equal-pressure torches are also called positive-pressure or medium-pressure torches.
exothermic reaction A chemical reaction that produces heat. The rapid oxidation of iron that is used to sever metal in oxyfuel cutting is an exothermic reaction.
face shield A rigid, transparent plastic sheet that covers the entire face to protect against molten metal, sparks, and spatter. Face shields are often worn with goggles to provide additional impact protection.
ferrous Containing iron. Ferrous metals, such as steels and cast irons, can be used with oxyfuel cutting.
filter plates The shaded protective lens inside a welding helmet that filters out harmful rays and intense bright light. The amount of shading required for a filter plate depends on the specific cutting process, materials used, and power source.
fire-resistant FR. Designed to resist burning and withstand heat. Fire-resistant materials for PPE are rated and must meet specific safety standards.
fittings A component that can connect, redirect, extend, or terminate the run of a gas hose. Fittings for oxyfuel gas hoses have either left-hand or right-hand threads depending on the type of gas.
flame cutting A thermal cutting process that uses a flame produced by a mix of oxygen and fuel gas along with a high-pressure stream of oxygen. Flame cutting and gas cutting are non-standard terms for oxyfuel cutting (OFC).
flame zones The visibly distinct areas of a flame. Flame zones are usually easily distinguished by their slightly different colors and cone shapes.
flashback A torch malfunction that occurs when the flame moves past the torch and into the gas hoses or gas cylinders. Flashback can cause explosions if not prevented or controlled.
flashback arrestors A device that prevents flames from reaching into the gas hoses or cylinders when flashback occurs. Flashback arrestors are integrated into torches or installed between the gas hoses and the torch and/or between the gas hoses and cylinders to prevent flashback from causing an explosion.
flow rate The amount of gas being moved in a certain amount of time. Flow rate can affect cut quality.
fuel gas A gas that can store potential energy and release it as thermal energy or that can be used to perform work. Fuel gases are mixed with oxygen to perform oxyfuel processes such as welding and cutting.
fumes Potentially hazardous gases and particulate matter generated by various manufacturing processes. Processes that produce fumes must use proper ventilation.
fuse plugs A safety device at the bottom of a gas cylinder designed to fail and melt if the cylinder is exposed to excessive pressures or heat. Fuse plugs help prevent acetylene cylinders from exploding.
gas cutting A thermal cutting process that uses a flame produced by a mix of oxygen and fuel gas along with a high-pressure stream of oxygen. Gas cutting and flame cutting are non-standard terms for oxyfuel cutting (OFC).
gas cylinders A metal container used to store gases under pressure for manufacturing purposes. Gas cylinders are built specifically for each gas and have different properties depending on the gas.
gas hose A flexible conductor used to transport gas. Gas hoses connect gas cylinders to the torch in oxyfuel cutting.
gauntlets A type of protective glove that extends past the end of the shirt sleeves to cover the arm. Gauntlets provide an additional level of protection when performing welding or cutting processes.
gouging A process that removes metal to create a groove in a workpiece or remove old, unwanted welds or imperfections from a workpiece. Oxyfuel cutting systems can be used to perform gouging.
graduated scales A series of measurement markings or lines that are divided into stages or quantities. Graduated scales are used on regulator pressure gauges to indicate the amount of gas pressure and to warn of any unsafe pressures.
hardenable Able to be hardened by normal heat-treatment processes. Hardenable metals are better able to resist penetration or surface scratching.
heat-affected zone HAZ. The area around a cut affected by the heat of the cutting process. The heat-affected zone does not melt, but its mechanical properties are altered by the heat of cutting.
hose connectors A fitting on an oxyfuel torch where the oxygen or fuel gas hose connects to the torch. Hose connectors are made of brass to ensure safety and durability.
ignition sources Any device or event capable of causing a fire or explosion. Ignition sources include open flames, sparks, static electricity, and hot surfaces.
ignition temperature The lowest temperature at which a heated substance or material spontaneously catches fire and continues to burn. Ignition temperature is also called kindling temperature.
injector nozzle The device in an injector torch that constricts the flow of oxygen before allowing it to enter the mixing chamber. The injector nozzle creates a high-pressure stream of oxygen that draws low-pressure fuel gas into the mixing chamber.
injector torches A type of oxyfuel torch with an internal injector nozzle that uses a stream of high-pressure oxygen to pull low-pressure fuel gas into the mixing chamber. Injector torches are also called low-pressure torches.
inlet-nipple seat The surface of the small opening on a regulator that connects to a gas cylinder and through which gas is drawn into the regulator. Inlet-nipple seats that are dirty or damaged may result in gas leaks.
inner cone The brilliant-white, conical zone of an oxyfuel flame that is located closest to the cutting torch tip. The inner cone often produces the most heat, and its size and definition depend on the ratio of oxygen to fuel gas.
intermediate cone The bluish-white, conical zone of a carburizing oxyfuel flame that separates the inner cone from the outer cone. The intermediate cone is unique to carburizing flames and is not present in either neutral or oxidizing flames.
intermediate pressure The pressure at which a double-stage regulator releases gas before reducing it to the working pressure. The intermediate pressure is the center point between the cylinder pressure and the working pressure.
iron oxide A metallic compound containing iron and oxygen. Iron oxides, such as rust and dross, are formed by a chemical reaction between iron and oxygen.
kerf A cut or opening created in a workpiece during a thermal cutting operation. Kerf sometimes refers to the width of a cut or the width of the material removed by a cutting process.
kilopascals kPa. A unit of pressure derived from the International System of Units (SI). The kilopascal unit measures the amount of load pressure that is applied over an area of one square meter.
kindling temperature The lowest temperature at which a heated substance or material spontaneously catches fire and continues to burn. Kindling temperature is also called ignition temperature.
kPa Kilopascals. A unit of pressure derived from the International System of Units (SI). The kPa unit measures the amount of load pressure that is applied over an area of one square meter.
left-hand threads A type of thread that fastens components when it is rotated counterclockwise. Left-hand threads are used on the fittings that connect fuel gas hoses to oxyfuel torches.
low-alloy steel A steel that contains small amounts of intentionally added materials that change the properties of the metal. Low-alloy steels may contain manganese, molybdenum, nickel, or other common alloying elements.
low-carbon steels A steel that contains between 0.05% and 0.30% carbon. Low-carbon steels are generally tough, ductile, and easily welded or cut.
low-pressure torches A type of oxyfuel torch with an internal injector nozzle that uses a stream of high-pressure oxygen to pull low-pressure fuel gas into the mixing chamber. Low-pressure torches are also called injector torches.
medium-pressure torches A type of oxyfuel torch that requires equal pressures of oxygen and fuel gas to ensure the gases reach the mixing chamber simultaneously and mix properly. Medium-pressure torches are also called positive-pressure or equal-pressure torches.
methylacetylene-propadiene propane MAPP. A colorless, flammable gas mixture made by combining three different gases. Methylacetylene-propadiene propane gas can be used for oxyfuel cutting applications.
mixing chamber The part of an oxyfuel torch where the oxygen and fuel gas combine prior to being burned by the flame. The mixing chamber may be located in either the torch head or the torch body.
natural gas A naturally occurring, flammable fossil fuel composed mainly of methane. Natural gas is sometimes used in oxyfuel cutting.
neutral flame A type of oxyfuel flame with a balanced proportion of oxygen and fuel gas. Neutral flames burn at around 5,589°F (3,087°C).
OFC Oxyfuel cutting. A thermal cutting process that uses a flame produced by a mix of oxygen and fuel gas along with a high-pressure stream of oxygen. OFC is sometimes called flame cutting or gas cutting, but these terms are non-standard.
orifice A hole at the end of a cutting tip. Orifice shape and size determines the applications for specific tips.
outer cone The blue-colored, conical zone of an oxyfuel flame that surrounds the inner cone, and sometimes, an intermediate cone. The outer cone is less defined and often produces much less heat than the inner cone, and its shape depends on the fuel gas used and the gas ratio.
overhand grip A method of holding an oxyfuel torch by placing the hand above it and wrapping the fingers around it, similar to holding a hammer. The overhand grip offers more stability than the underhand grip, but the torch becomes less maneuverable.
oxidizes Chemically combines and reacts with oxygen. In oxyfuel cutting, a stream of pure oxygen oxidizes the steel in preheated ferrous metals.
oxidizing flame A type of oxyfuel flame that contains more oxygen than fuel gas. Oxidizing flames burn at up to 6,300°F (3,482°C).
oxyfuel cutting OFC. A thermal cutting process that uses a flame produced by a mix of oxygen and fuel gas along with a high-pressure stream of oxygen. Oxyfuel cutting is sometimes called flame cutting or gas cutting, but these terms are non-standard.
oxyfuel cutting torch The device used to produce and control the flame that preheats and severs workpieces in oxyfuel cutting. Oxyfuel cutting torches combine fuel gas and oxygen to create the flame.
oxygen A colorless, odorless, tasteless gas that naturally exists in the atmosphere. Oxygen is the primary gas used in oxyfuel cutting.
personal protective equipment PPE. Any clothing or device used to minimize exposure to hazards and prevent injury. Personal protective equipment includes welding helmets, gloves, and earplugs.
pitted Marked with tiny holes. Pitted cut surfaces often result from using dirty or damaged oxyfuel cutting tips.
porous Full of holes or having many voids. Porous material inside an acetylene cylinder absorbs acetone, the liquid in which acetylene is dissolved.
positive pressure Pressure that is greater than the pressure of the surrounding environment. Positive-pressure torches rely on equal, positive pressures of oxygen and fuel gas to operate.
positive-pressure torches A type of oxyfuel torch that requires equal pressures of oxygen and fuel gas to ensure the gases reach the mixing chamber simultaneously and mix properly. Positive-pressure torches are also called equal-pressure or medium-pressure torches.
pounds per square inch psi. A unit of pressure used in the English system. The pounds per square inch unit measures the amount of load pressure that is applied over an area of one square inch.
preheat flame A flame produced by an oxyfuel cutting torch in order to bring a metal workpiece up to its kindling temperature prior to cutting. Preheat flames for oxyfuel cutting range in temperature from 5,000 - 6,000°F (2,760 - 3,316°C).
pressure gauges A device that measures the pressure of gas and displays it on a dial. Pressure gauges allow operators to monitor gas flow and determine when to adjust the regulator.
pressure marks Gouges in the surface of an oxyfuel cut. Pressure marks are caused by oxygen flow rates that are too high and travel speeds that are too slow.
pressure relief valves A component within a gas regulator that allows pressurized gas to escape if the pressure in the regulator reaches a critical point. Pressure relief valves prevent damage to regulators.
propane A colorless, flammable gas created during petroleum refinement processes that can be used in oxyfuel cutting. Propane is similar to propylene but outputs lower heat as it burns.
propylene A colorless, flammable gas created during petroleum refinement processes that can be used in oxyfuel cutting. Propylene is similar to propane but outputs higher heat as it burns.
psi Pounds per square inch. A unit of pressure used in the English system. The psi unit measures the amount of load pressure that is applied over an area of one square inch.
purges To clear an area of unwanted substances. Operators must purge oxyfuel gas hoses of ambient air before cutting and purge them of remaining oxygen and fuel gas after cutting.
ratio The relationship between two quantities. Ratios are usually expressed as fractions.
regulator The device used to control the amount of gas that flows from a cylinder. Regulators consist of a valve to control pressure and a gauge to measure the pressure flowing through it.
right-hand threads A type of thread that fastens components when it is rotated clockwise. Right-hand threads are used on the fittings that connect oxygen hoses to oxyfuel torches.
safety goggles A type of tight-fitting eye protection that completely covers the eyes, the sockets, and the surrounding facial area. Safety goggles offer protection from impact, sparks, molten metal, and spatter.
scale A flaky film that forms on the surface of a metal that has been heated to high temperatures. Scale on the surface of an oxyfuel cutting tip can result in a cut with a pitted or irregular surface.
seating faces The surface of the connection where a cutting tip attaches to the torch body. Seating faces should be kept clean and free from damage to prevent gas leaks.
setup All the necessary preparation of equipment that occurs before a welding or thermal cutting process can be executed. Setup includes collecting paperwork, tools, or materials and preparing machines.
shade rating The amount of shading provided by a filter plate. Shade ratings range from 1, which offers the least protection, to 14, which offers the greatest protection.
single-stage regulator A type of regulator that adjusts the cylinder pressure to the required working pressure in a single step. Single-stage regulators are usually less expensive than double-stage regulators.
smooth-jawed wrench A type of hand tool with flat jaws used to turn and tighten threaded fasteners and fittings. Smooth-jawed wrenches are more gentle than wrenches with toothed jaws and will not mar or damage sensitive brass fittings.
spatter Liquid metal droplets and sparks expelled during a thermal cutting or welding process. Spatter, which can spray up to 35 feet (10.67 m) from the work area, is a safety risk that can cause burns or fire.
stainless steel A type of steel that contains at least 10.5% chromium. Stainless steel exhibits excellent corrosion resistance.
steel An alloy of iron and carbon containing less than 2.0% carbon. Steel often contains other elements to enhance various properties of the metal.
striker An inexpensive and easy-to-use device that uses friction to safely ignite the fuel gas flowing from an oxyfuel torch. Strikers are also called spark lighters.
sustained backfire A torch malfunction that occurs when the flame moves up into the tip of the torch and continually burns inside the torch, sometimes moving as far back as the torch handle. Sustained backfire is considered extremely dangerous.
synthetic Artificial or human-made. Synthetic materials like nylon and polyester ignite easily.
thermal cutting A cutting process that uses heat to remove metal from a workpiece. Thermal cutting processes include oxyfuel, air carbon arc, plasma arc, and laser beam cutting.
tip cleaner A device used to remove carbon buildup from the orifices of an oxyfuel cutting tip. Tip cleaners come in a variety of sizes to fit different orifice diameters.
tolerances An acceptable deviation from a desired dimension that still meets specifications. Tolerances indicate the allowable difference between a physical feature and its intended design.
torch body The main part of an oxyfuel torch that connects the torch head and the torch handle. The torch body contains internal hoses that direct the flow of gases to the mixing chamber.
torch handle The part of an oxyfuel torch that the operator holds. The torch handle is located at one end of the torch body and may house components such as the hose connectors, torch valves, and cutting jet lever.
torch head The part of an oxyfuel torch that houses the cutting tip. The torch head is located at one end of the torch body and may house other components such as the mixing chamber.
torch valves A device on the torch used to regulate the amount of oxygen or fuel gas flowing into the torch. Oxyfuel torch valves use a specialized type of valve called a ball valve.
travel angle The angle formed between the cutting tip and the surface of the workpiece along the line of travel. Travel angles are measured from the side of the cut.
travel speed The rate at which an oxyfuel operator moves the torch along the workpiece to make a cut. Travel speed is measured in inches per minute (in./min or ipm) or millimeters per minute (mm/min).
turbulence A disturbance in the even flow of gas. Turbulence in an injector torch is caused by high-pressure oxygen exiting the injector nozzle.
underhand grip A method of holding an oxyfuel torch by resting it on the index and middle fingers and holding it in place with the thumb, similar to holding a pen. The underhand grip allows for more careful control of the torch, but it is not as easy to use as the overhand grip.
valve seat The circular surface upon which a closed gas cylinder valve lies. Valve seats that are dirty or damaged may result in gas leaks.
valve wrench A special tool used to safely open the valves of specific gas cylinders that is usually provided by the cylinder manufacturer. Valve wrenches are frequently required to open acetylene cylinder valves.
venturi effect The initial decrease and then subsequent increase in pressure that occurs when a gas or fluid passes through a constriction. Injector torches use the venturi effect to create a vacuum-like suction that allows high-pressure oxygen to draw low-pressure fuel gas into the mixing chamber.
welding A process that permanently bonds two separate components together. Welding uses heat, with or without pressure or friction, or a combination of methods to make a new part.
welding helmet A piece of personal protective equipment that consists of a hard face-guard and a dark-tinted filter plate. Welding helmets protect operators from flying debris and the intense light produced during welding and cutting processes.
work angle The angle formed between the cutting tip and the surface of the workpiece perpendicular to the line of travel. Work angles are measured from the end of the cut.
working pressure The pressure of the gas being delivered to the oxyfuel torch. Working pressure is much lower than cylinder pressure and thus suitable for use in welding or cutting operations.
working-pressure gauge The device that indicates the pressure of the gas being delivered to the oxyfuel torch. Working-pressure gauges are marked with a graduated scale that is specific to the type of gas in the cylinder.