LineBacker® 61™ NSF Certified Isolating Gaskets/Kits


The LineBacker® 61™ sealing system uses a rectangular sealing element in combination with a unique groove design to effectively seal and isolate flanges for potable water and other low-pressure fluid piping applications

NSF/ANSI Standard 61 establishes minimum health effects requirements for the chemical contaminants and impurities that may be indirectly imparted to drinking water. The LineBacker® 61™ Sealing/Isolating gasket is certified to conform with all criteria associated with NSF health effects testing, certification and production facility inspections.

Of particular importance with respect to NSF/ANSI Standard 61, is the micro-exposure of the sealing element (EPDM) within the G-10 Epoxy Glass retainer material. In addition to providing positive sealing characteristics relative to the fluid flowing in the pipe, the sealing element is also fully encapsulated between the flange and GRE retainer, reducing exposure of the sealing element to harsh outside atmospheric conditions.

For more information regarding NSF, please contact GPT Engineering.


  • Guards against blowouts¹
  • Usable with any type of flange or combination of flanges
  • Lowest possible clamp and compressive load to effect a seal
  • High dielectric strength 800v / mil
  • Water absorption less than 0.10%
  • All standard ANSI and AWWA flange sizes from 1/2″ and above


Retainer Physical Properties

Max Temperature +302°F /+150°C


ASTMTest MethodG-10 Epoxy Glass
D149Dielectric Strength:Volts/Mil(Short Time):690
D229Water Absorption:0.22 %
D790Flexural Strength:LW 66,000 psi / CW 60,000 psi (413,685 kPa)
D785Hardness Rockwell “M”:99
D638Tensile Strength:LW 45,000 psi / CW 39,000 psi (310,264 kPa)
D732Shear Strength:19,000 psi (151,684 kPa)

Seal Element Physical Properties

Temperature RangeEPDM
Fahrenheit-40° to +212°
Celsius-40° to +100°



  • Potable water and other fluids



Materials for flange isolation kits on pipes containing drinking/potable water (up to 280ºF (138ºC)) shall consist of the following components:

Isolating and Sealing Gasket

The full faced, NSF 61 certified, isolating and sealing gasket shall be LineBacker® 61™ Sealing Gasket (LB61) – Type “E”, 1/8” thick, G-10 retainer containing a precision tapered groove to accommodate the controlled compression of a EPDM quad-ring sealing element. Sealing element placement shall accommodate either flat, raised face or RTJ flanges. The quad-ring seal shall be pressure energized. The G-10 retainer shall have a 550 volts/mil dielectric strength and a minimum 50,000 psi compressive strength. The full-faced flange isolating gasket (weld-neck) shall be equal to or slightly smaller than the bore of the flange; (slip-on) shall be equal to or smaller than the I.D. of mating pipe.

Full Length Bolt Isolating Sleeves

One full length G-10 sleeve (extending half way into both steel washers) for each flange bolt. The G-10 shall be a 1/32” thick tube with a 400 volts/mil dielectric strength and water absorption of 0.10% or less.


Two, 1/8” thick, G-10 isolating washers for each bolt. Their compressive strength shall be 50,000 psi, dielectric strength 550 volts/mil and water absorption 0.10% or less. Two, 1/8″ thick zinc plated, hot-rolled steel washers for each bolt. The I.D. of all washers shall fit over the isolating sleeve and both the steel and isolating washers shall have a same I.D. and O.D.

Quality – (Made in U.S.A – A.R.R.A Compliant)

Flange isolating kits shall be manufactured at a facility that has a registered ISO 9001 Quality Management System. Submittals shall include copy of valid ISO registration and NSF 61 certification.

Before Tightening

The flange faces come into contact with the sealing elements, which extend slightly above the surface of the retainer. As the flange is tightened the sealing elements are compressed and move sideways into the inclined portion of the groove, developing a high unit pressure against the flange faces.

After Tightening

The flange faces have come into firm contact with the retainer, thus encapsulating the sealing elements within grooves. At the same time, the unique LineBacker® seal configuration provides elastic memory for elastomers not normally associated with this characteristic – resulting in a simple flat gasket with extremely high loading and self energizing characteristics without adverse cold flow problems.


The gasket retainer extends out to the O.D. of the flange. Holes are cut at the bolt circle to accommodate threaded studs or bolts.  If in doubt about whether to use an “E” type gasket or an “F” type gasket, select an “E” type gasket as it will perform well in both flange types.  An “F” type gasket only performs well in “F” type flange design.


The gasket retainer extends out to the I.D. of the bolt circle.