News & Tech Tips

How to Choose Rubber Gasket Thickness

When choosing the gasket thickness for compressed materials,  remember that thinner is better.  Most compressed sheet gasketing sealing values are based on 1/16” thickness.  Thicker materials require a greater compressive force to seal and have lower pressure ratings. The use of 1/16” thick gaskets will provide better sealing with lower bolt loading than 1/8” thick gaskets.  Thinner is better! 

Do you know your Viton®?

Many rubber materials claim to be Viton®, but are generic fluoroelastomers, or blends of other compounds with some Viton®. Blends generally have lower fluorine content and will not withstand exposure to many fluids and elevated temperatures the same way as genuine Viton®. All of the Viton® gaskets and sheet goods we provide are 100% Chemours Viton®. Count on Expert Gasket & Seal to provide the proper grade of genuine Viton® for your severe sealing application.

Durlon 9000 vs Virgin Teflon®?

Durlon 9000 will seal better than Virgin Teflon® (PTFE) in typical flange gasket service.  This is due to its construction, combining inorganic fillers with pure PTFE resins.  The result is a PTFE material that does not cold flow, yet retains the inert properties of Virgin PTFE.

Durlon 9000 is also easier to fabricate than Virgin PTFE, can be factory welded into large single piece gaskets, and is excellent for chemical, FDA, and pharmaceutical environments.

Please ask us about improving your Virgin PTFE application using Durlon 9000.

Spiral Wound Gaskets Color Codes

Spiral wound metallic gaskets used on standard ANSI pipe flanges are color coded on the OD edge to identify their winding & filler materials.  The most common is a yellow painted edge with a pink stripe.  This signifies a 304 stainless steel winding and Mica-Graphite filler.

Another common winding is 316 stainless steel with a flexible graphite filler.  Its color code is a green painted edge with a gray stripe.  There are many others spiral wound gasket color codes.   Please contact us for a color code chart that identifies the various combinations.

Rubber Hardness for Rubber Gaskets, Seals & O-Rings

Rubber hardness is expressed on the Shore A scale, and is measured with a durometer. The number may be specified as “60 Shore A”, or commonly as “60 durometer”. The number, itself, signifies the relative hardness within the A scale. Typically, the hardness of calendered rubber sheet ranges from 40A (soft) to 90A (very hard) in 10 point increments. Hardnesses below 40A are also available, though these sheets might be molded rather than calendered.

The most common rubber gasket hardness for Neoprene, Nitrile, and EPDM compounds fabricated from sheet is 60A, though softer and harder grades are also available. Red SBR (red rubber) is generally 75-80A, and Viton is typically 75A. Molded rubber products are available in hardnesses from 20A to 90A. O-ring hardness is usually 70A and, as with all rubber products, options are available.

All hardnesses have a tolerance of +/- 5 points. This means a 70A rubber can measure 65A, and a 60A rubber can also measure 65A; both would be acceptable. Because of the tolerance, it might be advisable to consider at least 20 point changes when testing the effect of particular hardnesses.

Please contact Expert Gasket & Seal with questions regarding rubber hardness for your rubber gasket, rubber seals, or rubber o-ring applications.

FDA Rubber Gaskets

FDA rubber gaskets are fabricated from rubber sheet that is made from FDA approved ingredients in compliance with Title 21CFR177.2600.  The gaskets, and the sheet from which they are made are not FDA approved – it is the ingredients used to produce the sheet that meet the requirements of Title CFR177.2600.  This regulation for rubber materials includes many compounds, such as Nitrile, Neoprene, Viton, Silicone, and others.  FDA gaskets are required in applications where the gasket comes in contact with food products.

Expert Gasket & Seal stocks FDA Nitrile & FDA Silicone in several thicknesses and can provide FDA rubber gaskets from other compounds as well.  Expert Gasket & Seal also provides non-rubber FDA gaskets from Teflon® and PTFE based materials such as Durlon 9000 & Durlon 9600.  Please contact us for assistance with your FDA application.

Boiler Handhole & Manhole gaskets

Handhole and Manhole gaskets for boilers are typically found in two shapes. Elliptical gaskets are an oval shape with a continuous curve and no straight sides. Obround gaskets have radius ends with parallel straight sides. Boiler gaskets are available in a number of materials. The most common rubber gasket is EPDM, suitable for hot water and steam up to 380º F. Expert Gasket & Seal provides EPDM Handhole and Manhole gaskets die-cut and molded in a variety of sizes.

Boiler Handhole and Manhole gaskets are also available in wire-inserted and plain woven fiberglass coated with a white SBR rubber for service up to 500º F. Also available are Spiral wound metallic gaskets that are used for higher temperature and pressure applications. These are provided in a wide range of metal and filler combinations; the most common are 304 stainless with a mica-graphite filler and 316 stainless with a Grafoil® filler.

Handhole and Manhole gaskets are specified by their inside length x width x flange width x thickness. Please contact Expert Gasket & Seal for assistance in choosing the correct Handhole and Manhole gasket for your boiler application.

Basic Rubber Compounds for Gaskets

Expert Gasket & Seal provides rubber gaskets for many types of service and applications. Here is a brief explanation of the most common rubber materials for gaskets and their intended usage.

Synthetic rubber is available in a variety of compounds for many different types of service. The most common of these are Neoprene®, Nitrile (Buna-N), EPDM, SBR (Styrene-Butadiene), Viton® (FKM), and Silicone.

Neoprene® (Chloroprene) is the most widely known synthetic rubber. Most chloroprene rubber compounds can be used in temperatures from -20°F to + 225°F, and in applications such as water, refrigerants, some mineral oils, and ammonia.

Nitrile (Buna-N, NBR, Acrylonitrile-butadiene) is designed for service in petroleum based fluids generally to 212°F. It is the material of choice for most mineral oils, some fuels, and petroleum based oils & grease. Nitrile is not compatible with glycol based brake fluid, phosphate-ester fluids, and high aromatic content fuels.

EPDM (Ethylene Propylene) is generally good within a temperature range of -50°F to +300°F and is the preferred compound for hot water, steam, glycol based brake fluids, alcohols, ketones, and phosphate-ester hydraulic fluids. EPDM is not compatible with petroleum based fluids.

SBR (Styrene-Butadiene) is the oldest synthetic rubber and was designed to replace natural rubber. It has a temperature range of -40°F to +180°F and is most commonly used in water applications. The most well known form of SBR used in gaskets is known as “Red Rubber”, named for it’s reddish-brown color.

Viton® (FKM, Flurocarbon) has excellent resistance to a wide variety of chemicals within a temperature range of -20°F to +400°F. Viton® is compatible with some acids, aromatic hydrocarbons (benzene, toluene) and methanol based fuels. Viton® also works well in high vacuum applications.

Silicone Rubber has excellent low and high temperature resistance (-75°F to +450°F) and is particularly ozone and weather resistant.

There are other compounds, besides these, available for gasket usage. Please contact Expert Gasket & Seal before choosing a rubber gasket. We will make sure you have the best, and most cost-effective compound for your rubber gasket application.

Selecting Custom Foam/Sponge Gaskets

The most common sponge gasket is a closed-cell rubber blend material. This material is reasonably resilient, has moderately good recovery, and is inexpensive. It can be provided plain, or with a pressure-sensitive adhesive on one side. Closed-cell sponges are available in a variety of elastomers for a wide range of applications. These materials work well in many situations, particularly those that have a constant squeeze on the gasket material.

Applications with alternating squeeze, such as doors that open and close, will benefit from using microcellular urethanes as gaskets. These materials exhibit almost zero compression set, have superior recovery, and are well suited for gaskets that have variable loads. They are particularly useful for electrical boxes and enclosures, and are available in UL listed grades for such applications. These materials, while somewhat more costly, out-perform typical closed-cell blended sponges where a seal must be maintained under imperfect seating conditions. They, too, can be provided plain or with a pressure-sensitive adhesive backing.

We stock a variety of sponge gasket materials, including Poron® and Griswold microcellular urethanes. Please contact us to discuss your application and be provided with a cost-effective solution for your sealing problem.

Choosing Basic Compressed Gasket Materials

There are several types of compressed gasket materials from which we fabricate gaskets, or provide the sheet for those wanting to make their own.

The most commonly used material we offer is Durlon® 8500, a green colored NBR binder/Aramid-Inorganic fiber compressed sheet.  Durlon® 8500 is excellent in steam, natural gas, and many petroleum based fluids, and covers a temperature range of -100 to 700ºF, with a continuous max of 548ºF.  For much of the same types of service, we offer a less costly alternate, Durlon® 7900.  Durlon® 7900 is an off-white colored NBR binder/Aramid fiber sheet with a max continuous temperature of 400º and is appropriate when service conditions are less severe.

For higher temperature steam and hot water service, we recommend Durlon® 8600, a white colored SBR binder/Aramid-Inorganic fiber sheet with a termperature range of -100 to 700ºF with a continuous max of 548ºF.

When a wider pH range is required, Durlon® 8400, a gold colored NBR binder/Phenolic fiber sheet is the logical choice.  Durlon® 8400 has a temperature range of -100 to 800ºF, with a continuous max temperature of 554ºF.   Durlon® 8400 is excellent in chemical, pulp and paper, and other industrial applications.

With the highest continuous max temperature of 600ºF, Durlon® 8300 should be considered for steam and hydrocarbon services in refining, petrochemical, and power generation industries.  Durlon® 8300, black in color, and with a NBR binder/Carbon fiber system, has a temperature range of -100 to 800ºF.

Durlon® 8700, blue in color, a CR (neoprene) binder/Aramid-Inorganic fiber sheet has the same temperature range as Durlon® 8500, but is used for refrigerants and other service requiring a neoprene binder.

There are many factors for each gasket application to consider before choosing a compressed gasket material.  Some of those include system pressure, media, temperature range, flange material and condition, flange design, and bolting.

Please contact Expert Gasket & Seal for additional assistance with your application.