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Viton® Oxygen-Compatible O-Rings

Dive Rite Express stocks a variety of DuPont Performance Elastomers Viton® brand O-rings
suitable for use in SCUBA applications.

Sizing -- Society of Automotive Engineers AS568B is an Aerospace Standard that specifies sizes for O-rings used in sealing applications. An AS568B number is a three-digit suffix that identifies the O-ring's size. Technically, an O-ring size is listed as AS568B-016, AS568B-112, etc., but most people use just the three-digit number. The first digit denotes the O-ring cross section width: 0xx = 1/16-inch, 1xx = 3/32-inch, 2xx = 1/8-inch. While it might seem convenient to provide a picture sizing chart, we've never seen an online version that could be reproduced exactly in a Web browser. Also, sizing an existing O-ring that has been in service can be error prone because O-rings can take a set that changes their dimensions enough to be misleading. Luckily, the sizes used in SCUBA applications are fairly regular, so it's probably best to choose the size based upon the application.

AS568B-	Outside Diameter	SCUBA Application Seal
214	1-1/4	Cylinder with Large Neck/Valve (3/4 NPS - All Aluminum, most Steel cylinders)
116	15/16	Cylinder with Small Neck/Valve (7/8 UNF - "Genesis" 3500 psi Steel cylinders)
112	11/16	Standard DIN Regulator/Valve (Nearly all DIN regulators)
111	5/8	Small DIN Regulator/Valve (You know if you need this one)
015	11/16	Cylinder Valve Bonnet Nut
014	5/8	Standard Yoke Regulator/K-valve
013	9/16	Large Low-Pressure Port/Hose (1/2 UNF)
012	1/2	High-Pressure Port/Hose (7/16 UNF) Manifold and Manifold Port Plugs
011	7/16	Standard Low-Pressure Port/Hose (3/8 UNF)
010	3/8	Low-Pressure Hose/2nd Stage Regulator Cylinder Valve Stem
003	3/16	High-Pressure Hose/SPG swivel

Materials -- O-rings can be made of a very long list of exotic materials; most are inappropriate for SCUBA applications. The materials commonly used in SCUBA applications appear in the following table.

Material	Description
Acrylonitrile-Butadine Copolymers (NBR or Nitrile)	Most O-rings used in SCUBA are made from Nitrile, a hydrocarbon based synthetic rubber. Nitrile offers excellent resistance to many oils and acids and has good physical properties. However, Nitrile is not a very oxygen resistant material and is not considered oxygen compatible. Nitrile is also often referred to as Buna-N.
Fluorocarbon Elastomers (FKM)	O-rings made of FKM have been the preferred choice for oxygen and nitrox compatibility in SCUBA diving applications. FKM is an elastomer with excellent oil and oxygen resistance at high and low temperatures, very good chemical resistance. Even for use with ordinary air, most experts agree that FKM O-rings outperform common Nitrile O-rings. Viton is DuPont Performance Elastomer's brand name for FKM.
Polyurethane (PUR)	The milky white O-ring occasionally seen in the face of K-valves, sometimes called a 10,000 psi O-ring, is made of Polyurethane. Polyurethane is very abrasion-resistant, but it is sensitive to UV light (sunlight).
Ethylene Propylene Diene Monomer (EPDM)	EPDM O-rings are becoming more common in SCUBA because some people feel it's a safer material for use in breathing air systems. EPDM is a elastomer with excellent weatherability, heat resistance, dielectric qualities and odor-free characteristics. However, EPDM is less resilient and is not recommended for use with petroleum derivatives.

Viton Brand FKM -- Viton is DuPont Performance Elastomer's brand name for fluorocarbon based elastomers (FKM). The Viton O-rings sold at Dive Rite Express are 100% virgin Viton family type "A." However, DuPont Performance Elastomers is not the only company that manufactures FKM products. Bear in mind that not all FKMs are equivalent, and there are even different types of Viton O-rings intended for various different applications. Many people incorrectly refer to any and all FKM O-rings or even generic "oxygen-compatible" O-rings as Viton. As a result, you could end up with O-rings that are not the type of Viton you need, let alone a Viton O-ring at all. Products not made from Viton may fall short of the expected performance.

Hardness -- O-rings are normally available with a hardness rating, as measured by an ASTM type-A durometer, of 70 (the "soft" kind) or more rarely a rating of 90 (the "stiff" kind). The O-rings sold on this page are 90-duro (except for the -003 SPG O-ring), and well suited for the SCUBA applications we describe. The soft O-rings are appropriate for dynamic applications where the O-ring is providing a seal with a constantly moving part, such as inside regulators. The stiff O-rings are more durable in static applications where the O-ring is providing a seal with stationary or occasionally moving parts, such as a valve.

Color -- O-rings are available in nearly any color, although most commonly seen in black. The Viton O-rings sold on this page are brown, simply to make them easily distinguishable from Nitrile O-rings which are usually black and EPDM O-rings which are often purple. Some people believe there is a difference in quality based on color, but that is more likely attributed to unknowingly using soft dynamic O-rings in static applications. Our O-ring manufacturer states there is little difference in quality for O-rings based on color alone, and independent testing supports that statement. Some people also incorrectly believe a Viton O-ring can be distinguished from a Nitrile O-ring by the surface appearance. Nitrile O-rings are said to have a shiny surface, and Viton O-rings are said to have a matte surface. This is not a reliable indicator, and certainly not true if the O-ring has been lubricated.

OEM-Supplied O-Rings -- Designers of SCUBA equipment often specify O-rings with special properties and materials for specific uses inside their equipment, particularly regulator internal o-rings. Substituting any other O-ring just because it's the right size can cause difficult-to-diagnose problems and degrade performance.

We are sometimes asked why we price most of our O-rings the same regardless of size. The reality is the bulk wholesale cost of a specific size O-ring is insignificant when we sell them to you one-at-a-time. What actually determines the price is the inventory investment and handling labor to sell a package of five O-rings.

[ Click for Prices ]

CHRISTO-LUBE® Oxygen-Compatible Lubricant

The preferred oxygen-compatible lubricant for SCUBA diving applications is CHRISTO-LUBE®. CHRISTO-LUBE MCG 111 is often specified where oxygen compatibility is required in dynamic O-ring lubrication; however, this lubricant actually works better than silicone grease (which is not oxygen-compatible) for nearly every type of SCUBA application. Dive Rite repackages CHRISTO-LUBE MCG 111 into cost-effective 0.5-ounce containers, a lifetime supply for most individuals.

Tek Tip

How Much and Where to Use Lubricant Some people very sparingly lubricate the SPG swivel O-ring. Some people also sparingly lubricate the threads of valves before they are installed in the cylinder neck. Do NOT lubricate the neck O-ring itself, and absolutely positively do not lubricate the valve/regulator seal O-ring or DIN threads. Most lubricant is used with dynamic seals in regulators and valves. As a general rule, the O-rings used with static seals in SCUBA applications should not be lubricated at all. The lubricant just causes contamination to stick to the surface of the O-ring and results in more problems with a static seal than any dubious benefit the lubricant might provide.

This three piece brass o-ring pick set is specifically designed for removal and placement of o-rings, but at Dive Rite Express we use them for all sorts of other tasks. The brass tips won't scratch soft seating surfaces in valves, regulators or other equipment and the color coded plastic handles have a comfortable ridged grip. Two of the tools have a sharp point and work well for removal, the third has a tiny ball on the end and is nice for placement. The set of three tools are in a re-sealable plastic package to help keep them organized and clean.

Image	Item		Description	Style	Ship	Price
	VA2564.5		Lubricant, Oxygen Compatible, 0.5-Ounce (CHRISTO-LUBE MCG 111)		Today	$17.50
	RB0894		Brass O-ring Pick Set, 3-piece		1-2 Days	$12.95
	V i t o n   B r a n d   O - r i n g s
	V568A-KIT		Viton O-ring kit, 50 pieces total, five each of 003,010,011,012,013,014,015,111,112,214		Today	$29.00
	V568A		Viton O-ring, brown, 90 duro, package of five	-214	Today	$3.00
				-116	Today	$3.00
				-112	Today	$3.00
				-111	Today	$3.00
				-015	Today	$3.00
				-014	Today	$3.00
				-013	Today	$3.00
				-012	Today	$3.00
				-011	Today	$3.00
				-010	Today	$3.00
				-008	Today	$3.00
				-007	Today	$3.00
				-006	Today	$3.00
	V568A -003		Viton O-ring, brown, 75 duro, package of five	-003	Today	$3.00
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