Engineering Associates Technical Help Series
Definitions of Pipe Sizes:
SDR: Standard Dimension Ratio is a standard which ensures the same
pressure rating for all diameters of pipe. Whether 1" or 24" in size, pipe
with a SDR-21 rating have the same pressure rating, such as the common 200 psi (Class 200).
Other common sizing is SDR-32.5 Class 125, SDR-26 Class 160 and SDR-13.5
Class 315, Class 200, Class 125, etc.: The "pressure class"
distinction tells you that the pipe is designed to withstand normal pressures
315 psi, 200 psi, 125 psi, etc. The industry standard is to have a built-in
safety factor of 2:1 for pressure surges, so a Class 200 pipe could probably
withstand 400 psi water hammer (shock) pressures.
Schedule 40/80: The "Schedule" distinction relates to actual wall
thickness, not pressure class. As pipe size increases, the relative strength
of Schedule pipe decreases; for example, 2" Sch.40 pipe is a higher
pressure class than 8" Sch. 40. Sch.80 is gray in color
and slightly thicker, and is used primarily for threaded fittings.
PIP, Sewer Pipe and Other Types: Other types/sizes of pipe (except
Polyethylene, described below) are not designed for pressurized irrigation
systems and should not be used. Try not to use some goofy type of pipe that
you "got from a friend", etc.
|Typical Pipe for
|Polyethylene Tubing: Black "poly pipe" is flexible irrigation
pipe which comes in rolls in sizes from 1/2" to 2", although the great majority of applications use 1/2" or 3/4". Advantages
include light weight, flexibility and easy no-glue fittings. The main drawback is that the pipe is simply not as
rugged as PVC,
and poly systems generally will not last as long. It should not be used for lawn sprinkler heads; it is best used for bubblers,
agriculture and drip irrigation. Contractors like it because it can be "pulled" or
plowed easily and is much less labor intensive to install.
|Schedule 40 PVC: Contractors will use this type of pipe for most residential or commercial jobs. Sch.40 PVC pipe and fittings offer the
best combination of strength and price for pipe sized 3/4" to 1 1/2". Class 200 is also
appropriate and commonly used for golf, municipal and other jobs using
pipe larger than 1 1/2", but Class 160 or under is not recommended. Unlike poly tubing, Sch.40 pipe can
withstand an occasional hit by a shovel or gophers. Solvent weld Sch.40 PVC
from 3/4" to 1" is the standard for home systems.
|Class 315 PVC: Half-inch pipe doesn't come in Sch.40;
it comes as Class 315. This is just a technicality: Class 315 pipe with Sch.40 fittings should be
used wherever 1/2" is needed.
|Sch. 80 PVC: The distinctive gray color separates Sch.80
from other types of pipe. It is thicker and stronger, but more expensive and not necessary for
small systems except for threaded risers for sprinklers or bubblers. Irrigation
systems generally do not use Sch. 80 pipe, but will use some threaded
|Slip Fittings v.s. Threaded: For the great majority of
situations, slip fittings (glue) are used. Threaded fittings are used at valves or where threaded risers for sprinklers or bubblers are
installed. Directional fittings for small systems are always glued. The glue or pipe cement is actually called "solvent welding", and
the process literally bonds or melts the PVC together. Make sure you
know how to glue!
|Pipe for Large Commercial, Municipal
|Class 200 PVC: We strongly believe that Class 200 PVC is the best choice for all pipe 2" and above in larger systems. It's
cost/strength ratio is excellent, unless money is no object or normal operating pressures are going to exceed
125 psi. Our opinion is that solvent weld for pipe 3" and under is fine, but
that pipe 4" and up should always be gasketed bell-joint.
|Gasketed PVC Fittings: These come in sizes from 2" to 24", but common irrigation sizes are 4" to 12". The cost of these
fittings is far less than ductile iron, but the strength certainly is much less as well. Gasketed fittings require a thrust block of
some kind to prevent leakage. We would not specify this type of fitting for pipe over 8" in diameter.
|Ductile Iron Fittings: These gasketed fittings are the strongest
type and require thrust blocking. If there's a tight budget, try to save money
elsewhere because the cost of using ductile
iron fittings is definitely worth it in the long run. As they appear, they are virtually
|Joint Restraints: Fittings which secure and brace pipe
bells, valves or directional fittings in a mechanical manner. These are used as an alternative to concrete thrust blocking, although it
is a more expensive system. Joint restraints are used much more in
potable municipal systems, but are now catching on for large irrigation
|Saddles and Main Line Taps: Saddles (shown) and taps are the means for diverting water from a mainline to lateral
lines or other devices. With saddles, a hole is drilled into the pipe and
this hardware is strapped on top. Tap-tees are like coupler fittings with a threaded outlet where a riser would be installed.
Look for wide double straps on saddles, as shown.
|Repair Couplings and Clamps: Repair fittings are part of every irrigation/grounds managers' regular routine. The wrap around type with rubber interior (shown) is very easy to install.
Ductile iron or PVC repair couplings are harder to install but definitely a permanent fix.
Always torque bolts (on all fittings) according to manufacturer.
Have all of your parts, rags, tools and glue handy. You probably don't want to wear your best clothes for
this....PVC glue has a habit of getting all over the place. Follow the tips at right for a good solvent weld, and
also read the labels of the primer and glue thoroughly to make sure that you have the right types. We recommend
blue or gray glue with purple primer; clear cement can be used where you can see the joint, such as above
ground anti-siphon valves or installations next to a front door.
Black Poly Pipe Tips:
There are two types of fittings: insert with barbs that go inside the pipe or compression fittings that go on the
outside. We like compression fittings, because once they're on it's extremely difficult to get the pieces apart.
Whichever you use, first lubricate the pipe and fitting with saliva or water. Next, press the pipe into/onto the fitting to it's fullest extent. The pipe
should be cut clean with a razor-sharp knife or shears. Unlike cement, poly is ready to be pressurized
immediately after installation. Before placing barb fittings, drip tubes and
emitters on the line, flush with clean water thoroughly. Make sure you install all the risers, lateral lines, drip tubes
or any other taps before backfill. When backfilling, it is particularly important with this type of
pipe to keep sharp rocks and debris away from the pipe.
Sunlight Damage to PVC and Gaskets:
All PVC pipe is sensitive to sunlight, therefore it should be kept in the
shade or under tarps until it is to be used. Pipe which has been sitting in the sun for any amount of
time should not be used for pressurized irrigation systems. It can be used for simple water transfers,
as drainage pipe or other uses. It's easy to spot pipe or fittings which
have sunlight damage: a yellow "sunburn" on the exposed side will be obvious.
Rubber gaskets for ductile iron or PVC fittings are also sensitive to sunlight,
so keep them in the shade as well. If the rubber appears to be warped, cracked,
baked or otherwise imperfect, do not install it or leaks will definitely appear