"DURHAM" OR "SCREW PIPE" WORK. PIPE AND FITTINGS
"Durham" or "screw pipe" work is the name used to denote that the
job is installed by the use of wrought-iron or steel screw pipe. We
speak of a "cast-iron job" meaning that cast-iron pipe was used for
the piping. A completely different method of work is used when
screw pipe is employed for the wastes and vents. When screw pipe is
to be used or considered for use, it is well to know something
concerning the various makes of screw pipe. Nothing but galvanized
pipe is ever used. The value of steel screw pipe and wrought-iron
screw pipe should be studied, and every person interested should,
if possible, understand how these different pipes are made and how
the material of which they are composed is made. In some places one
pipe is better than another and a study of their make-up would
enlighten the user and allow him to use the best for his peculiar
conditions. The maker's name should always be on the pipe. The
following table shows the sizes, weights, and thicknesses of screw
pipe:
-------+-----------+-------------
Size | Thickness | No. threads
| | per inch
-------+-----------+-------------
1-1/4 | 0.140 | 11-1/2
1-1/2 | 0.145 | 11-1/2
2 | 0.154 | 11-1/2
2-1/2 | 0.204 | 8
3 | 0.217 | 8
3-1/2 | 0.226 | 8
4 | 0.237 | 8
5 | 0.259 | 8
6 | 0.280 | 8
-------+-----------+-------------
Screw pipe work came into common use with the advance of modern
steel structures. Some difficulty had been experienced in getting
the cast-iron pipe joints tight and to keep the pipe so anchored
that it would not crack. The screw pipe was found to answer all of
the requirements of modern structures and therefore has been used
extensively. The life of screw pipe is not as long as extra heavy
cast-iron pipe. This is the only serious objection to screw pipe,
which must be renewed after a term of years, while extra heavy cast
iron lasts indefinitely. Screw pipe is never used underground. When
piping is required underground, extra heavy cast-iron pipe is used.
PIPING
The pipe used in Durham work is galvanized extra heavy, or standard
wrought-iron, or steel pipe. It is almost impossible to recognize
wrought-iron from steel pipe without the aid of a chemical or a
magnifying glass. To test the pipe to distinguish its base, take a
sharp file and file through the surface of the pipe that is to be
tested. If the pipe is steel, under a magnifying glass the texture
of the filed surface will appear to be smooth and have small
irregular-shaped grains, and there will also be an appearance of
compactness. If the pipe is iron, the texture will have the
appearance of being ragged and will show streaks of slag or black.
When screw pipe is cut there is always left a large burr on the
inside of the pipe. This burr greatly reduces the bore of the pipe
and is a source of stoppage in waste pipes. After the pipe is cut
this burr should be reamed out thoroughly. One of the strong points
of screw pipe is the strength of each joint. Care should therefore
be taken to see that perfect threads are cut on the pipe and that
the threads of the fittings are perfect. The dies should be set
right and not varied on each joint. There should be plenty of oil
used when threads are cut so that the thread will be clean and
sharp. The follower or guide on stocks should be the same size as
the pipe that is being threaded, otherwise a crooked thread will
result. If a pipe-threading machine is used, the pipe is set
squarely between the jaws of the vise that holds the pipe in place.
When cutting a thread on a long length of pipe, the end sticking
out from the machine must be supported firmly so that no strain
will come on the machine as the pipe turns. It is necessary to cut
crooked threads sometimes on the pipe to allow the pipe pitch for
drainage or to bring the pipe into alignment where fitting would
take up too much room. To cut a crooked thread on a piece of pipe,
simply leave the follower out of the stock or put in the size
larger. The dies not having a guide will cut a crooked thread.
Piping should be run with as few threads as possible. With a
thorough knowledge of and the intelligent use of fittings, a
minimum number of threads will result.
The pipes in a building are run in compact parallel lines in chases
designed especially for them. The tendency is to confine the pipes
to certain localities as much as possible. This makes a very neat
job and in case repairs are needed, the work and trouble incurred
will be confined to one section.
FITTINGS
The fittings used in screw pipe work are cast-iron recess type (see
Fig. 54). The fittings are so made that the inside bores of the
pipe and the fittings come in direct line with each other, thus
making a smooth inside surface at all bends. The fittings are all
heavily galvanized. All fittings should be examined on the inside
for any lumps of metal of sufficient size to catch solid waste
matter, and these must be removed or the fitting discarded. All 90 deg.
bends, whether Ts or elbows, are tapped to give the pipe that
connects with them a pitch of at least 1/4 inch to the foot.
Except where obligatory, 90 deg. fittings should not be used. To make a
bend of 90 deg. a Y-branch, a nipple and a 45 deg. bend should be used, or
two 45 deg. bends will make a long easy sweep of the drainage pipes and
reduce the possibility of stoppage.
Y-branches are inserted every 30 feet at least to allow for a
clean-out which can be placed in the branch of the fitting. When a
clean-out is placed an iron plug should not be used. These plugs
are not removed very often and an iron plug will rust in and be
almost impossible to get out. Brass clean-out plugs are used and
are easily taken out.
At times it is necessary to connect cast iron and wrought iron, or
in a line where a union could be used if the pipe were not a waste
pipe, a tucker fitting is used. This fitting is threaded on one end
and has a socket on the other to allow for caulking. To get a good
idea of all the fittings in general use, the reader should get a
catalogue from one of the fitting manufacturers and a survey of it
will give the names and sizes of the fittings. However, I show a
few common ones. In the writer's opinion, the studying of the
catalogue would be of more benefit than a description of fittings
at this point. The sizes used and the methods employed to vent the
waste-pipe systems are the same as in cast-iron work.
HANGERS AND SUPPORTS
The hanging of screw pipe is a very essential point. The taking of
the strain off from a fitting or line of pipe by the use of a
hanger is the means of avoiding serious trouble after a job is
completed. On horizontal runs hangers are placed not more than 8
feet apart. In a building constructed of wood, the hangers are
secured to the joists. In a building constructed of steel beams and
concrete the hangers are secured to the steel beams by means of
I-beam hangers that clamp on the beams; also in the case of
concrete the hangers are extended through the floor and a T is put
on the hanger on top of the cement floor; an iron bar or a short
piece of smaller pipe run through the T holds the hanger in place
and secures it rigidly. The finished floor is laid over the hanger
so that it does not show from the top. Hangers on the vertical
lines should be placed at every joint and under each fitting. To
have the pipe in true alignment, the hangers must be hung and
placed in line. Every riser line must have an extra support at the
base to avoid any settling of the stack which will crack the
fittings and break fixture connections.
MEASUREMENTS
The proper installation of screw pipe work requires getting correct
and accurate measurements. Every plumber is or should be able to
get correct center to center, center to end, end to end, center to
back, and end to back measurements. In Durham work 45 deg. angles are
continually occurring. To get these measurements correctly, the
following table has been compiled as used by the author and found
to be correct. The reader should memorize it so that it may be used
without referring to the book.
MEASUREMENTS
------------+------------+-------------
Soil pipe | Screw pipe | Multiplier
------------+------------+-------------
1/6 bend | 60 | 1.15
1/8 " | 45 | 1.41
1/12 " | 30 | 2.
1/16 " | 22-1/2 | 2.61
1/32 " | 11-1/4 | 5.12
1/64 " | 5-5/8 | 10.22
------------+------------+-------------
Before any measurements are taken, the lines of pipe are laid out
and the position of each fitting known. As I have stated before,
the plumber must look ahead with his work. He must have the ability
of practically seeing the pipe in place before the work is started.
This requires experience and judgment. Before the measurements are
taken and the pipe cut consideration must be given to the fact that
the fittings and pipes must be screwed into position. Therefore,
"can the fitting on the pipe be placed where it is laid out when
this is considered?" must be one of the many questions a plumber
should ask himself. Allowance must be made for the chain tongs to
swing. Whenever possible, a fitting is made up on the pipe while
the pipe is in the vise.
[Illustration: FIG. 76.--The offset is B or 12 inches center to
center. The offset is made using 45 degree fittings. Therefore the
length of A from the center of one fitting to the center of the
other is B x 1.41 = 12 x 1.41 = 16.92 inches.]
FIXTURE CONNECTIONS
The fixture connections when screw pipe is used are necessarily
different than when cast-iron pipe is used. A brass nipple is wiped
on a piece of lead pipe and then screwed into the fitting left for
the closet connection. The lead is flanged over above the floor and
the closet set on it. The lead is soldered to a brass flange. The
brass flange is secured to the floor and then the closet bowl
secured to the brass flange. Another method employed is to screw a
brass flange into the fitting so that when it is made up the flange
will come level with the floor; the closet bowl is then secured to
this flange. There are a number of patented floor flanges for
closet bowl connections that can be used to advantage. Slop sinks
have practically the same connections as the closets. Other
fixtures such as the urinal, lavatory, and bath, can be connected
with a short piece of lead wiped on a solder nipple, or the
trimmings for the fixture can be had with brass having iron pipe
size threads, and the connection can then be made directly with the
outlet on the waste line. This is a very general way to describe
the connections, but space will not allow a detailed description of
these connections. It is always well to allow for short lead
connections for fixtures so that the lead will give if the stack
settles.