Plumbing for Glassblowers

Rev. ... 2002-03-21, 2003-02-27, 2004-01-15, 2005-11-21, -12-05
2006-02-25, 2008-01-26

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Copper Working Tools


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
Tubing brass flare union fitting Tubing brass flare nut Tubing brass flare connecting adaptor
Union (or connector) Flare nut used on tubing Flare union to tapered pipe



Copper tubing working tools
The tools in these two pictures cost $20-30 and allow working with all sizes of soft copper tubing for applying flare fittings. In the left picture, the grey tool is a small to medium sized cutter with a triangular reamer extended. The tubing is cut by snugging the cutting wheel - on the silver bar, center - against the tubing with knob to the left, tubing being held by the rollers to the right. The tool is rotated around the tubing once and the knob is turned to move the cutting wheel in more. When cut through, the reamer removes the sharp edge forced into the tubing by the pressure. Tubing is flared using the silver bar with counter sunk holes to clamp the tubing - it starts with the end of the tubing even with the surface. The nut must placed on the tubing first. The red tool is placed as shown on the right and the T handle turned to force the cone into the end of the tubing, pushing out the edge to a flare as shown in the left photo (both photos enlarge if double clicked.)

Tubing cutter, flared tubing, and flaring tool

Flaring tool for copper tubing with tubing in place.


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 for black iron pipe Tee joint for black iron pipe Street Elbow for black iron pipe Union for black iron pipe
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.


Copper tubing with flare fittings used to connect tank to iron pipe.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 connections shown are duplicates for the gloryhole and furnace. The iron pipes on the right of the picture go down 4 ft. and cross to the concrete slab at dirt level. They then rise over the edge of the slab (below) and run around it. The extra elbows and short nipples keep rain out of the pipes when not connected and aim the copper fitting in the right direction. A 3/8" NPT to Flare (Fine) brass adaptor allows connection of the copper.
This is the other end of the iron pipe at the glory hole. The pipe ends at a cutoff valve which also adapts to the fine thread copper flare nut. At the other end of the copper, an adaptor and reducer take the 3/8" tubing down to 1/4" NPT for the existing burner piping, which includes a needle valve for volume control. (Burner.htm) (since this picture was taken, the iron elbow was changed to a T and a pressure gauge installed.)
Same connection at different angle, showing blower and wood valve.
Curving pigtail in copper used to connect iron pipe to removable burner
Blower and wood air valve with new copper gas connections on glory hole.
Below is the use of two elbows with a short nipple to turn a corner, rise up from ground level over a slab edge and head off in a new direction that is not 90. Although not clear, the incoming pipes are entering from the right in the grass. The right elbow is in the glory hole line, the left leading around back (see right) to the furnace. Street Elbows used to turn a corner with some flexibility, unlike a single 90 elbow at the price of extra space and cost. Here a standard elbow connects to a pipe leading to the tank and turns flow vertically. The street elbow (one female, one male connection) takes the outgoing pipe at the top into the elbow. The joint can be tightened to the correct angle.
Elbows turn a corner and rise over a slab A street elbow with an elbow turns a corner at note quite 90


Low pressure flex tubing.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.

Pipe thread engagement standards drawing


Male threads:  Measure the outside diameter of the large portion of the thread at "A"; Find figure nearest this dimension in column 1 or 2 of chart. The dimension in column 3 will be your nominal pipe thread size.

Female Threads: Measure top diameter of thread at "B"; Find figure nearest this dimension in  column 1 or 2 of chart. The dimension in column 3 will be your nominal pipe thread size.

Column 1 Column 2     Column 3   Column 4 Column 5
OD Approx. (fraction) Inch. for quick reference only Actual (decimal) Inch.
See note below on
 using these columns
Nominal Pipe
 Thread Size
ID Normal engagement
 for tight joint
(dimension "C")
Threads per Inch
19/64 (3/8-) .301 0.946 15/16 1/16   1/4 27
13/32 (3/8+) .405 1.272 1 9/32 1/8   1/4 27
35/64 (1/2+) .540 1.696 1 11/16 1/4 0.364 3/8 18
43/64 (5/8+) .675 2.121 2 1/8 3/8 0.493 3/8 18
27/32 (7/8-) .840 2.639 2 5/8 1/2 0.622 1/2 14
1-3/64 (1-1/8-) 1.050 3.299 3 5/16 3/4 0.824 9/16 14
1-5/16 1.315 4.131 4 1/8 1 1.049 11/16 11-1/2
1-21/32 (1-5/8+) 1.660 5.215 5 7/32 1-1/4 1.38 11/16 11-1/2
1-29/32 (1-7/8+) 1.900 5.969 5 31/32 1-1/2 1.61 11/16 11-1/2
2-3/8 2.375 7.461 7 15/32 2 2.047 3/4 11-1/2
These two columns are the circumference, which can be measured by wrapping a piece of paper around the pipe, marking the overlap, then flattening the paper and measuring between the lines.  It is Pi (3.14159) times column 2.
ID is computed from actual OD and thickness of Sched. 40 (common) pipe given here.


What is gallons of water in 100' pipe
 You need the true ID of the pipe, since 1/2", 3/4", 1" are nominal and neither the OD or ID is that size.

1/2" 3/4" 1" Nominal Pipe Size
0.633 0.824 1.049 Diameter Inside-True
0.316 0.412 0.525 Radius Inside
0.0999 0.1697 0.2756 R squared
0.313 0.533 0.866 Pi R sq. (
0.002217 0.00370 0.00601 sq ft.
0.2217 0.370 0.601 cu.ft in 100 ft.
    7.48 U.S.Gallons in cu.ft  
1.63 2.77 4.499 gallons

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