gasses -- compressed gas cylinder and tank information

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Disposable propane cylinder threads are usually 7/16th UNEF. In addition there is an automatic valve in the fitting activated by a pin inside the female fitting. Simply screwing a hose with a 7/16th UNEF fitting will not allow you to use the bottle. The fitting with both the threads and pin are called Type 1 or QCC-1 fittings. Don't expect even sales people to know this.

Medium cylinders use Acme threads Large cylinders (>40 pounds) use NO, I think this may be wrong. My notes are unclear. Double cheek and correct 1"-20 UNEF threads (called POL threads)

  • Outlet threads: 1"-20 UNEF
  • Inlet threads: 0.880-14 NGO-LH-EXT

1-5/16" Female Acme Inlet

1/4" male NPT

Disposable non-reusable (non-refillable) cylinders

For Oxygen (Worthington, Bernzomatic 1.4 ounce/40.1 g) the working pressure is likely 400 PSI (from non-authoritative sources). This seem plausible because the cylinders are regulated by "Title 49 CFR 178.65 - SPECIFICATION 39 NON-REUSABLE (NON-REFILLABLE) CYLINDERS", which specifies a maximum working pressure of 500 PSI.

For 20 pound (5 gallon) Liquefied Propane cylinder (type 4BA) the pressure will vary by temperature. At 70 degrees Fahrenheit the pressure should be 145 PSI. This rises to 315 PSI at 130 degrees Fahrenheit (max recommended storage temperature. Transportation temperature may be different). See Publication NFPA58. The service pressure is specified at a maximum of 240 PSI. The DOT requires tanks to be tested every 12 years to twice the service pressure (480 PSI). Burst pressure is not specifically regulated for Type 4AB, but designs are typically regulated to minimum burst pressure of four times service pressure (960 PSI). This is confusing because pressure at 130 degrees would be over service pressure. This may because service pressure may be lower than storage pressure... Small, disposable 1 pound/465g tanks likely have similar ratings (due to the physics of the liquid propane you can't mandate a lower pressure for liquefied propane). Burst pressure is likely lower, so beware.

Relief valves may be removed using a tire valve stem remover (center hole may need to be drilled out larger to fit). Obviously do no remove relief valves from tanks under pressure.

See File:REP 10202 Battelle Cylinder Report Final.pdf.

CGA: Compressed Gas Association

post valve fitting often used in O2 for human use (medical, supplemental).
valve fitting used for O2 regulators in welding
valve fitting used for acetylene regulators in welding.
acetylene regulator inlet (internal thread) to acetylene tank valve outlet.
oxygen regulator inlet (internal thread) to oxygen tank valve outlet.
propane regulator inlet to propane tank outlet. The same as or compatible with POL fittings.

left handed threads

acetylene regulator outlet

code for hose fittings

Decode thread/valve specifications. AS 2473 Type 10.5 (5/8" BSP RH Ext) VI1, AS 2473 Type 20 (5/8" BSP LH Ext), 5/8"-18 UNF RH Ext, 5/8"-18 UNF LH Ext

Vertical Inlet
Side Inlet
Left Hand thread
Right Hand thread
External thread (male)
Internal thread (female)
National Pipe Tapered (not Thread -- we know it's a thread)
National Pipe Straight -- this thread is most often found today in electric lamps.
Male National Pipe Tapered
Female National Pipe Tapered
a thread standard for small to medium sized Propane tanks. Also known as a CGA 510 fitting. The POL acronym originated from the company that first manufactured these fittings -- the Prest-O-Lite company.
Overfill Protection Device. A float valve inside the tank shuts off the filler tube as the level of propane liquid rises to a preset level. OPD also refers to OPD Acme threads, which are the type of threads found on OPD valves. The threads are distinctive because they are so large. They only make two complete turns around the outside of the tube. These valves are usually rated at 375 PSI.
liquid propane gas
Compressed Natural Gas -- similar to Propane, but mostly methane and lighter than air. Propane is heavier than air.

The terms male and female are not used as often with gas threads because certain fittings may seem to be male, but have internal threads. Fittings for 1-pound disposable propane tanks are a good example.

Acetylene Type B tank thread
9/16-18 left hand threads.
Propane 1 pound disposable thank threads
1"-20 UNEF threads? Need to check this. The tank itself is male thread. The 1-20 UNEF likely refers to the hose end adapter. Note that these fittings also have an internal spring loaded valve. The valve actuator is female. The hose adapter has a male pin that presses on the spring in the valve to open the tank.
Propane 40 pound tanks
Water/Oil/Gas Pressure -- the G in WOG does not refer to gasoline; it refers to pressurized/compressed gas -- usually natural gas, propane, methane, etc. The WOG designation usually has a number printed before it that indicates pressure in PSI -- 1000WOG is 1000 PSI, 2000WOG is 2000 PSI.
Cold Working Pressure -- ratings are often stated for a component at "normal" ambient temperature; although, this the range is often -29°C to 38°C (-20°F to 100°F), which are temperatures you might find anywhere outdoors on Earth. Outside this range the pressure rating of the fitting should be derated.
control valve
this is a valve designed to throttle or limit flow. These valves may not allow a flow to be completely closed.

Thread Confusion

Why are there so many different, weird threads? The threads on compressed gas tanks were standardized this way deliberately to make it difficult to accidentally combine tanks, gasses, and fittings in unsafe ways. Simply marking a tank or painting it different colors is not enough to prevent tanks from getting mixed up. You don't want the wrong tank screwed into your oxygen supply when you are having surgery.

Welding O2 vs. Medical grade O2

Most compressed gas suppliers will have a large dewar bottle of O2 that they use to bill both medical grade and industrial grade O2 tanks. It's most likely safe to breath from industrial grade O2 tanks, but the supplier does not have to promise that. Medical grade O2 tanks are also designed and made differently and have different standards and requirements for inspection. Medical grade also often requires a dive license or doctor's prescription to purchase. It may seem silly, but don't argue with the gas man. The rules are complex not just to annoy you. It's a simple matter to attach a medical fitting to an industrial tank. Bring that setup to be filled and you may be refused. You can buy or make an adapter... In my case, I wanted to use medical tanks for industrial applications. The gas supplier may be more tolerant of this. You can find a greater variety of sized and weights for small medical thanks. The smallest common industrial tanks for 20 cubic foot steel, which are not huge, but are still 15 pounds. While you may find a gas supplier with no legal objection to filling your bottle they may simply not want to. It's as much effort for them to fill a 20 cubic foot tank as a 125 cubic foot tank. It's not so bad if you lease a thank and simply exchange them. They fill a big batch of the little tanks all at once. But you can't do an exchange with a weirdo, custom bottle. They would have to fill it while your wait. A saner approach would be to lease a big bottle of oxygen. Take it home and use it to transfill your little bottles. You can find transfill adapters for this purpose.

In practice, it's no less expensive for a gas supplier to store and supply industrial grade O2 than medical grade O2. In reality they may charge you more for medical grade O2. Don't argue with them.

gas valves

DuraChoice 1/2" Stainless Steel (316) Ball Valve -- 2000 WOG (water, oil, gas), 2000 PSI