Plumbing for Glassblowers

Plumbing for the glass worker primarily involves gas, air, and compressed air, with only a bit of water if really needed. The primary materials for piping these fluids are PVC - a white rigid plastic, copper tubing, and threaded steel pipe, commonly called "black iron pipe."

While water can use PVC pipe to great convenience, gas, being flammable, has considerable restrictions against it and compressed air should use the metal connections as PVC has proven dangerous in the higher and changing pressure environments - with reports in woodworking magazines of broken PVC traveling like a rocket across the room to splinter on the other side.  Large PVC is commonly used for blower air distribution to burners where the pressure is only a few pounds. The same problems in a fire with gas in plastic occur with gas in metal with soldered joints, thus flared or threaded joints in copper tubing and iron pipe will constitute most connections in a glassblowing studio.

For design of plumbing systems as to size of pipe and reductions on branching, see pressure

There are two sets of metal fittings that concern the glassblower, those for soft copper tubing and those for black iron pipe.  With these two the whole shop can be plumbed, although rigid copper sweat soldered and plastic PVC pipe glued up are options for water.

Soft copper tubing can be connected several ways, but flared fittings are appropriate and legal for gas, air, and water.  Gas fittings must not be soldered and compression fittings are less common especially for larger tubing used to carry the main gas flow.  Shown below are two connectors and the flare nut used to fasten the tubing to the fittings.  The right hand image shows a fitting to connect soft copper to pipe threads.  The advantage of copper tubing is that it can be formed to make long runs without extra fittings, being bent around corners.  The chief downside is that it is soft and can be damaged after installation if stepped on or hit.

Brass fittings for flared copper tubing

Union (or connector)	Flare nut used on tubing	Flare union to tapered pipe

Black Iron Pipe
Standard pipe fittings are tapered so they seal as they are turned tight. Threads in joints are commonly covered with thin Teflon tape or goopy pipe dope to aid sealing.  Standard white Teflon joint tape is NOT rated for gas and an alternate should be used.   Dope is not supposed to be used on compression and flare fittings.   All joints with gas should be tested with soap and water for bubbles.  Black iron pipe is used for gas because natural gas in particular will peel galvanizing off and clog valves, etc. Pipe can be easily bought in 10 foot lengths, threaded both ends.  Nipples are short pieces, from about 2" up to 12".  Most hardware stores will have 2', 3', 4' & 6' pieces.  A serious pipe threading tool is costly - $150-200 with costs of $50 or so for additional dies to cut other sizes of thread.  Hex dies can be bought for smaller pipe threads for occasional work.

Black iron pipe fittings

Connector Joining pipes by twisting one against the other.	Straight T Joining pipes while adding a third	Street Elbow See example use below	Union - Nut in middle releases joint without twisting pipe

Plumbing connections to my furnace & glory hole were modified and added 2002-03-14ff. Previously, the glory hole had been run off flexible torch hose rated for propane. This was replaced with 3/8" black iron pipe in areas where I will be walking and stepping and with 3/8" copper tubing at the ends to provide a union connection and flexibility in moving the tanks and the burners.

Note that 3/8" NPT is a nominal size based on the inside of water pipe when it was cast iron and the ID was 3/8" the OD being .675" and not having changed as materials allowed a thinner wall. Black pipe is used because galvanized water pipe sheds its coating when exposed to natural (and propane?) gas, blocking orifices, etc. Joints for gas piping can not use Teflon tape used on water joints because it is not approved for gas according to the label. Pipe dope (like thin putty) is used or specially rated tape.

Copper 3/8" is exactly 3/8" OD. There are actually two different flare fitting threads I could have used, the fine thread being chosen because it is used on flex tubing (see below for limits). Note that soft soldered fittings are not allowed with gas because in the event of a fire, they would melt and release more gas. Tools There are actually several different methods of attaching fittings on copper, including compression and soldering that are not covered here.

The tank to right holds 100# or 20 gallons of propane. I own two and swap them. As currently rigged, there are two high pressure regulators on the tank both adjustable, one more easily than the other. The pressure coming out of the tank is about 175 psi, that coming out of the regulators is up to 12 psi. Low pressure gas (natural or propane) is in the area of 6-7 inches of water, which is about 4 ounces per sq. inch (28 inches height difference in a water manometer=1 psi.)

The tubing shown is commonly used for heaters (and in a larger version) for stoves to connect the rigid pipe to the fittings and allow movement of the unit. It is stainless steel corrugated for flexibility and is required by law. The label must be left on when installed. It is low pressure connection tube and specifically cannot be used over 8" of gas pressure. Where it can be used, rubber or other flammable tubing must not be used due to the release of gas in a fire.

PIPE SIZES - This chart was from A&J Fittings Inc. (before added columns) which no longer shows it. FAMOUS PLUMBING SUPPLY essentially the same table. Note that for the first three pipe sizes, the actual pipe size is more double the nominal.