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 flangeconnection, although it wastes material and may make tightening more difficult due to interference with nearby system components.
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 torque.
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 continueinstallation. 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 1/8�.
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 before proceeding.
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 two holing procedure.
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 anti seize 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 hand tighten all of the nuts until none remain loose. Now the flange assembly will remain in place as you prepare to fully tighten it.
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 ANSI B16.5:
For the installer�s convenience, the pattern is also indicated by numbers molded into the vinyl flange next to each bolt hole.
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 isgiven 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 whiletightening 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 GF representative.
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-to flange 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 maximumlisted 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 pressure testing.
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 after installation.
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