Standard Operating Procedure
Task: Replacing Gas Cylinders
Submitted by: Miller Lab at UNC (Andrew Walden)
Date: 5/29/2014
Revision Date (Author): 9/10/2015 (Kate Pitman)
Potential Hazards:
- Falling gas cylinders
- High Pressure gasses
Restrictions:
- Lab safety training
Materials Needed:
- Crescent wrench
- Gas cylinder cart
- Teflon tape
Background:
- Users should understand basic regulator operation before manipulating gases at high pressure.
Illustration:
Procedure:
- Removing the regulator
- Assess the situation: know what gas you are changing, who might be using the gas, etc. Make sure no reactions are in progress that might be affected by the cylinder switch.
- Close the main cylinder valve on top of the cylinder.
- For toxic gases like CO, make sure to purge any residual gas into the hood: once the cylinder valve is closed, vent the residual gas through a bubbler or hose leading into a hood. The pressure gauges should read 0 psig for both cylinder and delivery pressure. Then close the delivery valve.
- Using a crescent wrench loosen the regulator nut, connecting the regulator to the cylinder. If there is any residual pressure, you will hear a hiss as a small amount of gas in the regulator is released. After you have loosened the nut it should be unscrewed the rest of the way by hand. Make sure to support the weight of the regulator as you are unscrewing it.
- As soon as the regulator has been removed the cap on top of the cylinder should be replaced.
- Moving cylinders
- Note: Cylinders should only be moved with the regulator removed and cap screwed on. (unless a regulator protector safety cap is installed)
- Get the gas cylinder cart and move it next to the outgoing cylinder.
- Unstrap the empty cylinder and carefully roll it onto the gas cylinder cart. Secure the cylinder with the chain and carefully move it to be stored with other empty cylinders for pick up. Even empty cylinders should be double strapped. Label all empty cylinders using tape with the word “empty” or letters “MT” written on it.
- Find a new cylinder of the appropriate gas and move it into position using the cylinder cart. New cylinders should still have a plastic covering on the valve under the cap.
- Roll the new cylinder into position and secure it using two straps. Remove the cap and store it in a convenient place near where the cylinder is being used.
- Regulator information
- Check the CGA numbers on both the cylinder and the regulator to make sure that they match. On most cylinders this number will be printed on a flat portion of the cylinder directly bellow the valve. On many regulators the CGA number will be printed on the regulator nut or underneath the dials.
- Note: Never use a regulator that is incompatible with the gas you are using. The cylinders and regulators for flammable gasses are reverse threaded to ensure that they are only used together. The nuts on these regulators will also often be marked with a series of notches.
- Some common CGA numbers are listed here. (A more complete list can be found at the end of this document)
- CGA #580: Nitrogen, Argon, Helium
- CGA #350: CO, Ethylene, Hydrogen, Methane, Regeneration gas
- Attaching the regulator
- Make sure that all old Teflon tape is removed from the regulator and the cylinder threads.
- Apply one complete wrap of new Teflon tape to the exposed threads (usually the nut on the regulator) and tighten the nut while supporting the weight of the regulator. Use a crescent wrench to fully tighten the nut (usually another 1/4-1/2 of a turn).
- If the regulator has not been used recently — or you are unsure of the pressure setting — turn the regulator dial all the way to the left so that it will be set to its lowest pressure delivery setting.
- Leak testing
- Once the regulator has been attached, it should be leak tested.
- Make sure that the delivery valve is closed.
- Open the valve on the top of the cylinder. The cylinder pressure gauge should increase to about 2000 psi for most cylinders. The delivery pressure gauge should read 0 psig (the delivery gauge does not increase until there is flow through the regulator). Make a note of the pressure; a piece of tape is a good method. Then shut off the cylinder valve. If the pressure does not drop over the course of a few minutes there are no serious leaks between the cylinder and the regulator.
- Next open the cylinder valve again as well as the delivery valve on the regulator. Again make a note of the pressure and then close the cylinder valve and watch to ensure that the pressure does not drop over a few minutes.
- If no leaks are detected open both the cylinder valve and delivery valve fully and adjust the regulator delivery pressure if necessary. Turing the regulator dial clockwise will increase the delivery pressure while turning it counterclockwise will decrease the delivery pressure.
- End of use
- When the cylinder is not actively in use (connected to a piece of equipment and properly supported), the regulator must be removed and the cap reattached.
| Pure Gases | CGA Number |
| Acetylene | 510 |
| Air (industrial) | 590 |
| Allene | 510 |
| Ammonia (anhydrous) | 240, 260, or 705 |
| Ammonia (electronic) | 660 or 720 |
| Air (medical) | 346 |
| Argon | 580 |
| Carbon dioxide | 320 (n.b. fitting requires a special washer) |
| Carbon monoxide | 350 |
| Chlorine | 660 |
| Deuterium | 350 |
| Ethylene | 350 |
| Helium | 580 |
| Hydrogen | 350 |
| Methane | 350 |
| Nitrogen | 580 |
| Oxygen | 540 |
| Propane | 510 |
| Propylene | 510 |
| Lecture Bottles | CGA Number |
| Non-corrosive lecture bottles | 170 |
| Corrosive lecture bottles (use a purge valve) | 180 |
| Gas Mixtures | CGA Number |
| CO2 / Argon | 580 |
| H2 / N2 (regeneration gas) | 350 |
| H2 / CO (synthesis gas) | 350 |
| Natural gas | 350 |