Plastic Tanks and the Installation of PVC Flange Fittings and considerations for Torque Settings
Please read all instructions before attempting to install flanges.
Q: Will GF support me if a flange fails during installation or
A: Yes. A factory expert is available daily to help guide you
through the installation process and resolve problems.
If a GF product is defective, we will replace it. Our
customers’ satisfaction is our primary goal.
Item #M275 (5/09)
Flanges may be used when the piping system may need to be dismantled
• the installation is temporary or mobile
• transitioning between dissimilar materials that can not be cemented together
• the installation environment is not conducive to solvent cementing
Why Choose a Vinyl Flange?
Like all vinyl pipe and fittings, vinyl flanges are lightweight,
inexpensive, and easy to install. However, PVC and CPVC
have different physical properties than metals, and
therefore special care is required to ensure that your vinyl
flanges have a long, reliable service life. Installers should
study these instructions and follow them carefully in every
installation in order to ensure satisfactory performance
and enjoy the full benefits of the GF warranty.
When using a vinyl flange, ensure that the entire system
is well-supported and that the flange does not bear the
weight of a massive, unsupported system component such
as a cast iron valve. See support instructions in the GF
Technical Manual online:
Vinyl Flanges PVC
Visually inspect flanges for cracks, deformities, and solvent
cement or other obstructions on the sealing surfaces.
A rubber gasket must be used between the flange faces
in order to ensure a good seal. For Schedule 80 flanges,
GF recommends a 0.125” thick, full-face gasket with
Shore A scale hardness of 70±5, and the bolt torque
values published below are based on this specification.
For other hardness requirements, contact GF Technical
Services. Select the gasket material based on the chemical
resistance requirements of your system.
A full-face gasket should cover the entire flange-to-flange
interface without extending into the flow path.
Size (in) O.D. (in, min) I.D. (in, max)
½ 3.50 0.88
¾ 3.88 1.10
1 4.25 1.38
1¼ 4.63 1.60
1½ 5.00 1.93
2 6.00 2.44
2½ 7.00 2.91
3 7.50 3.59
4 9.00 4.64
6 11.00 6.82
8 13.50 8.66
10 16.00 10.81
12 19.00 12.09
It is critical to avoid excessive compression stress on a
vinyl flange. Therefore, only low-friction fastener materials
should be used. Low-friction materials allow torque to be
applied easily and gradually, ensuring that the flange is
not subjected to sudden, uneven stress during installation,
which can lead to cracking.
Either the bolt or the nut, and preferably both, should be
zinc-plated to ensure minimal friction. If using stainless
steel bolt and nut, lubricant must be used to prevent high
friction and seizing. In summary, the following fastener
combinations are acceptable:
• zinc-on-zinc, with or without lube
• zinc-on-stainless-steel, with or without lube
• stainless-on-stainless, with lube only
Cadmium-plated fasteners, while becoming more
difficult to obtain due to environmental concerns, are
also acceptable with or without lubrication. Galvanized
and carbon-steel fasteners are not recommended. Use
a copper-graphite antiseize lubricant to ensure smooth
engagement and the ability to disassemble and reassemble
the system easily.
Bolts must be long enough that two complete threads
are exposed when the nut is tightened by hand. Using a
longer bolt does not compromise the integrity of the flange
connection, although it wastes material and may make
tightening more difficult due to interference with nearby
Bolt Size (in)
Size (in) &
½ 4 2½ ½-UNC ½ SAE3
¾ 4 2½ ½-UNC ½ SAE
1 4 2½ ½-UNC ½ SAE
1¼ 4 3 ½-UNC ½ SAE
1½ 4 3 ½-UNC ½ SAE
2 4 3 5/8-UNC 5/8 SAE
2½ 4 3½ 5/8-UNC 5/8 SAE
3 4 3¾ 5/8-UNC 5/8 SAE
4 8 4 5/8-UNC 5/8 SAE
6 8 4¾ ¾-UNC ¾ F4364
8 8 5¼ ¾-UNC ¾ F436
10 12 6 7/8-UNC 7/8 F436
12 12 6½ 7/8-UNC 7/8 F436
1 Suggested bolt length for flange-to-flange connection with
0.125” thick gasket. Adjust bolt length as required for other
types of connections.
2 Minimum spec. Use of a stronger or thicker washer is always
acceptable as long as published torque limits are observed.
3 Also known as Type A Plain Washers, Narrow Series.
4 ASTM F436 required for larger sizes to prevent warping at high
A washer must be used under each bolt head and nut. The
purpose of the washer is to distribute pressure over a wider
area, reducing the compression stress under the bolt head
and nut. Failure to use washers voids the GF warranty.
Compared to metals, vinyls are relatively flexible and
deform slightly under stress. Therefore, not only must
bolt torque be controlled in order to avoid cracking the
flange, but continuing to tighten the bolts beyond the
recommended torque levels may actually make the seal
worse, not better.
Because bolt torque is critical to the proper function of a
vinyl flange, a current, calibrated torque wrench accurate
to within ±1 ft-lb must be used when installing vinyl flanges.
Experienced installers may be tempted to forgo the use
of a torque wrench, relying instead on “feel.” GF does not
endorse this practice. Job-site studies have shown that
experienced installers are only slightly better than new
trainees at estimating bolt torque by feel. A torque wrench
is always recommended.
Never use an impact wrench to install a vinyl flange.
Checking System Alignment
Before assembling the flange, be sure that the two parts
of the system being joined are properly aligned. GF has
developed a “pinch test” that allows the installer to assess
system alignment quickly and easily with minimal tools.
First check the gap between the flange faces by pinching
the two mating components toward each other with one
hand as shown below. If the faces can be made to touch,
then the gap between them is acceptable.
Next check the angle between the flange faces. If the faces
are completely flush when pinched together, as shown
above, then the alignment is perfect, and you may continue
installation. Otherwise, pinch the faces together so that
one side is touching, then measure the gap between the
faces on the opposite side. The gap should be no more than
To assess high-low misalignment, pull the flange faces
flush together. If the faces are concentric within 1/8”, then
the high-low misalignment is acceptable.
If the gap between the mating components can not be
closed by pinching them with one hand, or if the angle or
high-low misalignment between them is too large, then
using the bolts to force the components together will result
in excessive stress and possible failure during or after
installation. In this case, inspect the system to find the
greatest source of misalignment and refit the system with
proper alignment before bolting.
The pinch test is a good rule of thumb, but always use
common sense as well. If it seems difficult or awkward to
pull the flange faces together, then stop the installation and
either refit the system or consult your GF representative
Bolt Hole Alignment
The bolt holes of a Van Stone flange will align automatically
at the bolts are inserted and tightened. No additional
adjustment is necessary.
To align the bolt holes of a fixed flange, use standard twoholing
Placing the Gasket
Center the gasket between the flange faces, with the bolt
holes aligned with corresponding holes in the gasket. A
full-face gasket cut to the specified dimensions (see Table
1) should come just to the inner edge of the flange face near
the flow path, or overlap the edge slightly.
Inserting the Bolts
If using copper-graphite antiseize lubricant as
recommended, apply the lubricant evenly with a brush
directly to the bolt threads, and to the nut if desired. Cover
the bolt from its tip to the maximum extent to which the nut
will be threaded.
Insert bolts through washers and bolts holes as shown:
Tighten all nuts by hand. As you tighten each nut, the nuts
on the other bolts will loosen slightly. Continue to handtighten
all of the nuts until none remain loose. Now the
flange assembly will remain in place as you prepare to fully
Again, when hand-tightened, at least two threads beyond
the nut should be exposed in order to ensure permanent
engagement. If less than two threads are exposed,
disassemble the flange and use longer bolts.
Tightening the Bolts
Vinyl flanges require gradual, even bolt tightening.
Tightening one bolt to the maximum recommended torque
while other bolts are only hand-tight, or tightening bolts in
the wrong order, produces uneven stresses that may result
in cracking or poor sealing.
To ensure even distribution of stresses in the fully-installed
flange, tighten the bolts in a star pattern as described in
For the installer’s convenience, the pattern is also indicated
by numbers molded into the vinyl flange next to each bolt
The torque required on each bolt in order to achieve
the best seal with minimal mechanical stress has been
carefully studied in laboratory and field installations, and is
given in Table 3.
To ensure even distribution of stresses and a uniform seal,
tighten the bolts to the first torque value in the sequence,
using a star pattern, then repeat the star pattern while
tightening to the next torque value, and so on up to the
maximum torque value.
Vinyls, like all polymers, deform slightly under stress. A
final tightening after 24 hours is recommended, when
practical, to ensure that any bolts that have loosened due to
relaxation of the polymer are fully engaged.
If a flange leaks when pressure-tested, retighten the bolts
to the full recommended torque and retest. Do not exceed
the recommended torque before consulting an engineer or
Multiple-Pass Bolt Torque
Size (in) Torque Sequence
1st 2nd 3rd 4th 1st 2nd 3rd 4th
½ 3 5 - - 5 8 - -
¾ 3 5 - - 5 8 - -
1 3 5 - - 5 8 - -
1¼ 3 5 - - 5 8 - -
1½ 3 5 - - 5 8 - -
2 5 8 - - 5 10 12 -
2½ 5 8 10 - 10 15 18 -
3 5 12 15 - 15 20 25 -
4 10 15 20 - 15 25 32 -
6 12 24 30 - 20 32 42 -
8 15 35 40 - 30 40 50 60
10 25 50 60 - 20 40 60 70
12 30 60 72 - 20 50 65 80
* Assumes the use of SS, zinc- or cadmium-plated bolt and/or nut
along with copper-graphite antiseize lubricant brushed directly onto
the bolt threads.
** Assumes the use of zinc- or cadmium-plated bolt, nut, or both.
Never use unlubricated, uncoated bolts and nuts with vinyl flanges,
as high friction and seizing lead to unpredictable torque and a high
incidence of cracking and poor sealing.
Note that the torques listed in Table 3 are for flange-toflange
connections in which the full faces of the flanges
are in contact. For other types of connections, such as
between a flange and a butterfly valve, where the full face
of the flange is not in contact with the mating component,
less torque will be required. Do not apply the maximum
listed torque to the bolts in such connections, which may
cause deformation or cracking, since the flange is not fully
supported by the mating component. Instead, start with
approximately two-thirds of the listed maximum torque and
increase as necessary to make the system leak-free after
Keep Instructions Available
Provide a copy of these instructions to every installer on the
job site prior to beginning installation. Installers who have
worked primarily with metal flanges often make critical
mistakes when installing vinyl flanges. Even experienced
vinyl installers will benefit from a quick review of good
installation practices before starting a new job.
Best practices include tagging each flange with
• installer’s initials
• installation date
• final torque value (e.g., “29.2-31.5”)
• confirmation of 24-hour torque check (“y” or “n”)
This information can be recorded on pre-printed stickers,
as shown below, and placed on each flange immediately
Experience has shown that installation tags speed up
the process of resolving system leaks and product
failures, improve communication between the contractor
and distributor or manufacturer, highlight training
opportunities, and promote worker diligence.
© Georg Fischer LLC 2009 Link to original data
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