"1/2-inch" Poly Tubing is
not 1/2 inch

Drip Irrigation
Supply Tubing& Fittings
by Stuart Spaulding, CLIA

Certified Landscape Irrigation Auditor
Training & Communications Manager at DIG Corp.

The polyethylene supply tubing produced today for drip
irrigation systems is a far superior product compared tothe tubing that was manufactured in years past.

Significant advances in extruding technology and refinements inthe processing and blending of raw materials have led to theproduction of polyethylene tubing that has a longer lifespan, ahigher resistance to UV rays, and greater protection from thermal
degradation. In short,todays drip irrigation
poly tubing will stayflexible and functional
for decades even if it
is exposed to direct
sunlight in challenging

environments.

Unfortunately, there is one aspect of drip irrigation
poly tubing that remains unchanged, and thatis the fact that the tubing is still “nominally”
sized. Unlike PVC pipe, there is no industry
or global standard for the outside diameter(O.D.) of poly tubing. Currently, there are threedifferent sizes of so-called 1/2″ poly tubing;they all have slightly different inside (I.D.) andoutside diameters, and none of them are 1/2″!
It may help to make the comparison to the way
lumber is specified…take a common two-by-fourfor example. They are sold in the lumber yard ina variety of lengths under the two-by-four name,but the actual height and width are not 2″ by4″. The typical dimensions are closer to 1.5″ by
3-3/8″, but they have always been called twoby-fours. This is a good example of a nominally
sized commodity.

Inside and Outside Diameter& Compression Fittings
The three main sizes of so-called
1/2″ poly tubing are:1.

There are three different sizesof so-called 1/2″ poly tubing;they all have slightly different
inside (I.D.) and outside
diameters, and none of themare 1/2″!

.520″ ID X .620″ OD

Smallest of the three, becoming
obsolete, uses compression fittings
with green inserts.

2.

.600″ ID X .700″ OD

3.

.620″ ID X .710″ OD

The most common size in retail stores,
uses black compression fittings.

Sometimes called 5/8″, may have ablue stripe, takes compression fittings
with a blue insert.

T

he outside diameter is critical when it
comes to selecting compression fittings,
because these fittings seal against the outsideof the tubing. The tubing is connected to thefitting by forcing the end of the tubing into
the fitting while moving it from side to side,
gradually, until the end is about 3/4″ inside thefitting.

The outside diameteris critical when it
comes to selecting
compression fittings
The fitting has an interior lip that allows thetubing to go in but not out. These fittings aredesigned for one-time use and are not easily
removed from the tubing after installation.
Compression fittings are available in a varietyof configurations including coupler, elbow, tee,end cap, hose adapter and more (fig. 1).

fig. 1 Compression fittings

Universal PolyTubing Fittings
The universal type of tubing fittings are available
in a variety of designs that typically utilize a.710″ Compression
Tee (blue inserts) for.710″ PolyTubing.700″ Compression
End Cap for.710″ Poly Tubing.710″ Compression
Elbow (blue inserts)
for .710″ Poly Tubing.700″ Compression
Coupling for .700″
Poly Tubing

threaded nut to connect the fittings to all threeof the sizes of 1/2″ poly tubing. They cost a bit
more than basic compression fittings, but they
are very useful, especially when the installer is
not certain of the tubing size. These fittings canalso be removed and re-used if necessary. The

New Installations

variety of configurations is more limited however,

It is not so difficult to determine the outsidecoupler.

and are usually only available in tee, elbow ordiameter of the tubing in the store or online.
The outside diameter is usually printed on
the outside of the tubing itself, or on theproducts’ packaging or label.

And since

the compression fittings are color coded,
it’s easy to select the proper size. Use theall black fittings for .700″ OD tubing, green
for the .620″ and blue for the .710″ OD polytubing. Stores should stock the appropriate
fittings for the tubing they sell. Please beaware that most stores stock more than one
size of poly tubing.

Existing Installations
It is not uncommon for identification problems
to occur when installers are dealing with existing
systems. This is because over time, the letteringon the outside of the tubing can fade away, andthere may be no color-coded fittings available
to indicate the tubing size. The less common.620″ OD poly tubing is noticeably smaller thanthe larger sizes, but even a trained, experienced
person cannot easily notice the difference
between .700″ & .710″ tubing. One way to judge
the size of the tubing is by how it fits into a fitting.
The tubing should require a fair amount of effort
to force into the fitting, but not too much. If it
slips in easily then the fitting is probably too large
for the tubing. But if this is too problematic, fear

Universal Nut Lock™
Tee

universal nut-lock fittings
will fit all three sizes of1/2″ poly tubing.

Hydraulic Specifications/Limitations
FLOW RATE:

Since the poly tubing

is the main supply line for majority of noncommercial drip irrigation systems, it is very
important to know how much water it candeliver without creating hydraulic problems
like excessive water velocity or pressure.
Remember that drip systems apply water atlower pressure and at lower flow rates (gallonsper hour-GPH) than sprinkler systems (gallonsper minute-GPM). Of course, the larger theinside diameter, the more water the tubing cannot, there is a solution; universal fittings are now

deliver. The maximum flow rate for .700″ OD

available that will fit all three sizes of 1/2″ polytubing.

220 gallons per hour. This means that the total

and .710″ OD poly tubing is approximately

Universal Nut Lock™
Elbow

Universal Nut Lock™
Coupling

There are two types offittings that can be usedwith 3/4″ poly tubing.

of the flow rates for all the emission devices
connected to the line should not exceed 220GPH.

DISTANCE LIMITATIONS: TheSpecialized compression fittings are available

maximum distance limit for 1/2″ poly tubing de-inpends on the flow rate but a safe number to use

many

configurations(similarto1/2″

is not to exceed 350′ for any single run length.

compression fittings) which fit over the outside

OPERATING PRESSURE:

poly tubing are barbed insert fittings andof the tubing. Also available for 3/4″ and 1″

The poly

adapters which are forced into the end of thetubing should be used on drip systems onlytubing and are sometimes held in place with aand operated in the range of 20 to 40 psi. This

hose clamp.

usually means that a pressure regulator should
be installed to lower the dynamic (operating)pressure. The tubing is typically rated to handle
a maximum of 60 psi., but it never should beinstalled upstream of a remote-control valve,

3/4″ Spin-Loc tee
for 3/4″ poly tubing

where it will be subject to continuous pressure.

1″ insert (barbed) tee
for 1″ poly tubing

Larger Sizes ofPoly Tubing

When selecting either of these fittings, it isThe 1/2″ sizes of drip supply tubing are thethe larger diameter poly tubing will be easieressential to identify the ID and/or OD of thetubing and verify that it is compatible with thefittings selected. Like the smaller 1/2″ tubing,most common sizes in use today, but there

to work with after it is uncoiled and laid out

are also larger sizes produced and installed,

in direct sunlight for about 20 minutes. This

although they are mainly used in commercial

will warm the tubing and make it more pliable

and agricultural installations.

and easier to force into fittings, and reduce theThe 3/4″ and 1″ tubing can be run for a much longer.820″ ID X .940″ OD
Also known as 3/4″ poly tubing,maximum flow rate = 450 GPH
1.060″ ID X 1.200″ OD
Also known as 1″ poly tubing,maximum flow rate= 700 GPH

distance that the 1/2″ poly and are often used as aheader or as a supply line to feed 1/2″ poly tubing
laterals. These larger sizes are typically used oncommercial drip/low-volume irrigation systems
with higher total flow rates which connect to an
automated irrigation valve.

tendency to re-coil during installation.

Closing Comments
We hope that the information contained in thisarticle can help to inform the installer, do-ityourselfer and designer to the facts about theseproducts with the goal to ultimately reduce theheadaches and problems that can occur due tolack of knowledge and/or installation experience.
More information and details about poly tubing,fittings and other drip irrigation products areavailable in print and online, and many freeresources are available at www.digcorp.com or
www.irrigation.org. Thank you for reading andplease keep an eye out for our next blog, which
will attempt to clarify and inform you about anotheraspect of drip and low-volume irrigation systems.

•