Scuba Diving O-Rings

Scuba Diving O-rings

Many items of scuba diving equipment contain rubber O-rings that perish, dry out and develop cracks as time goes by. Even if the dive gear is not used, once it is a few years old, all the O-rings will need replacing.

An O-ring is a doughnut, or torus shaped seal typically used to prevent the passing of air or fluid. In other words, O-rings are used to keep fluid or air IN or OUT of a defined space. For example, an underwater camera housing uses O-rings to keep water out, and scuba regulators use O-rings to prevent precious air from escaping.

Just as barbed wire and duck tape seems to fix everything on land, O-rings and tie wraps seem to fix anything when you're at sea. These tiny rubber rings are crucial parts of a variety of scuba diving gear and equipment. O-rings prevent leaks at the seams of scuba gear and are a vital part of your life support equipment while diving. O-rings are used in scuba regulators, underwater lights and strobes, dive computers and cylinder/tank valves, and may often break due to pressure and wear and tear.

If you work on dive gear you know the importance of having the correct O-rings. Many of the O-rings used on cylinders, valves and regulator hoses are pretty much generic. Having a large selection of common O-rings is a must for the serious technical diver.

However, if you aren't well versed in the technical aspect of scuba gear, it's only advisable to attempt to change the O-ring on a scuba cylinder/tank valve (Yoke), or the face of your DIN regulator. Leave other O-rings for experienced professionals.

The information that follows should help you to know more about the O-rings used in various scuba diving applications.

O-Ring Sizing

In the USA the Society of Automotive Engineers (S.A.E.) publishes AS568B as an Aerospace Standard that specifies sizes for O-rings used in sealing applications. The equivalent British Standards Institution publication is BS1806, which lists all Imperial standard sizes. This standard includes all of the 5 main cross section groups in AS568, plus several sizes that are "between" AS568 sizes. In Australia BS1806 is widely referenced in many industries, including the dive industry.

The BS1806 number is a three-digit suffix that identifies the O-ring's size. Technically, an O-ring size is listed as BS1806-016, BS1806-112, etc., but most people use BS and the three-digit number (e.g. BS112), or just the three-digit number (e.g. 112). 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. However, you can download and print our Scuba O-Ring Sizes Chart (Adobe PDF | 356.37 KB) — Chart showing scuba diving O-ring sizes.

Please remember that 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 'user serviceable' SCUBA applications are fairly regular, so it's probably best to choose the size based upon the application.

BS1806- OD ID CS SCUBA Application Seal
214 1-1/4" 1"
1.000"
1/8"
0.139"
Cylinder with Large Neck/Valve (3/4" NPS)
(All Aluminum, most Steel cylinders)
Duro: NBR 90, FPM 90
116 15/16" 3/4"
0.750"
3/32"
0.103"
Cylinder with Small Neck/Valve (7/8" UNF)
("Genesis" 3500 psi Steel cylinders)
Duro: NBR 90, FPM 90
112 11/16" 1/2"
0.500"
3/32"
0.103"
Standard DIN Regulator/Valve
(Nearly all DIN regulators)
Duro: NBR 70/90, FPM 75
111 5/8" 7/16" 3/32"
0.103"
Small DIN Regulator/Valve and Old Yoke Valves (You know if you need this one)
Duro: NBR 70, FPM 70
110 9/16" 3/8" 3/32"
0.103"
MDE Yoke Valves
Duro: NBR 90
015 11/16" 9/16" 1/16"
0.070"
Cylinder Valve Bonnet Nut
Duro: NBR 70, FPM 70
014 5/8" 1/2"
0.500"
1/16"
0.070"
Standard Yoke Regulator/K-valve
Duro: NBR 90, FPM 70
013 9/16" 7/16" 1/16"
0.070"
Large Low-Pressure Port/Hose (1/2" UNF)
Duro: NBR 70, FPM 70
012 1/2" 3/8" 1/16"
0.070"
High-Pressure Port/Hose (7/16" UNF)
Manifold and Manifold Port Plugs
Duro: NBR 90, FPM 90
011 7/16" 5/16" 1/16"
0.070"
Standard Low-Pressure Port/Hose (3/8" UNF)
Duro: NBR 70, FPM 70
010 3/8" 1/4"
0.250"
1/16"
0.070"
Low-Pressure Hose/2nd Stage Regulator Cylinder Valve Stem
Duro: NBR 70, FPM 70
006 1/4" 1/8"
0.125"
1/16"
0.070"
BC Power Inflator
Duro: NBR 75, FPM 75
003 3/16" 1/16" 1/16"
0.070"
High-Pressure Hose/SPG swivel
Duro: NBR 90, FPM 90

 
O-Ring Materials

O-rings can be made of a very long list of exotic materials and 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
(FPM/FKM/Viton®)
O-rings made of FPM/FKM/Viton® have been the preferred choice for oxygen and nitrox compatibility in SCUBA diving applications. FPM/FKM/Viton® 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 FPM/FKM/Viton® O-rings outperform common Nitrile O-rings.
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.

 
The Difference between FPM, FKM and Viton®
The terms FPM, FKM and Viton® very often cause confusion and lead to incorrect interpretations. All of these designations actually stand for one single base material: fluoro rubber.

  • FPM is the international abbreviation according to DIN/ISO.
  • FKM is the short form for the fluoroelastomer category according to the American standard ASTM.
  • Viton® is the registered trade mark of DuPont Performance Elastomers.

O-Ring 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 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.

O-Ring Colour:

O-rings are available in nearly any colour, although most commonly seen in black. Most FPM/FKM/Viton® O-rings are black. The FPM/FKM/Viton® O-rings typically sold for scuba diving are brown, simply to make them easily distinguishable from Nitrile O-rings which are usually black and EPDM O-rings which are often purple. Just to be clear, the COLOUR of the O-ring is MEANINGLESS.

Some people believe there is a difference in quality based on colour, 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 colour alone, and independent testing supports that statement.

Some people also incorrectly believe a FPM/FKM/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 FPM/FKM/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.

How to Replace Your Cylinder/Tank Valve O-ring

Brass O-ring Tools Remove the old O-ring visible in the orifice of the tank's regulator valve. For this you should use a brass O-ring pick which looks similar to that of a dental pick (pictured right). This is because metal tweezers or other objects can damage the o-ring groove, and even the slightest dent of the groove can cause leaks. A plastic toothpick too is a safe tool to use if you don't have an O-ring pick.

Using the pick, scoop the old O-ring out and clean out the groove using the same plastic toothpick or professional pick. Look out for sand or debris and keep an eye out for any corrosion. If you spot any, you may want to have a professional take a look at it.

Check your replacement O-ring against the one you removed. Confirm they are of similar size and materials.

Push the new O-ring into the groove to replace the old one. It should slip in easily. If you have to stretch or force it, it's probably not the right size. Never use silicone grease. This is especially to be avoided if you are using a nitrox mix (a combination of nitrogen and oxygen). Silicone reacts with oxygen. Avoid using anything other than your finger or the back eraser end of a pencil to seat the O-ring.

Make sure the new o-ring you just put in doesn't have any nicks, cuts or stretch marks on it. If it does, replace it with a new one again.

Test the new O-ring, by attaching the first stage of your regulator like you would normally do. Slowly open the cylinder valve to pressurize the regulator. If you hear a loud pop or clap and air hissing out, the O-ring is not properly seated. Go back to the beginning and try again.

Trident Brass O-Ring 3 Piece Tool Set Trident Brass O-Ring 3 Piece Tool Set
RRP: $67, Our Price: $61, You Save $6 (9%).
This tool set combines three brass picks for the removal of O-rings from regulators, scuba tanks valves and so on.

Apeks O-rings

Apeks Regulator Travel Kit
Apeks Regulator Travel Kit

This table lists the O-Rings used for servicing Apeks regulators for the following models:
* First stages: US4, DS4, UST, DST, FST(ATX100), FSR(ATX200)
* Second stages: T20, TX40/50/100/200, AT20, ATX40/50/100/200

Apeks ID BS Cross Sectn. Inner diam. SCUBA Application Seal
- 003 1/16 1/16 High-Pressure Hose/SPG swivel
AP6403 004 1/16 5/64 High-Pressure Hose/SPG swivel (less common)
AP1299 006 1/16 1/8 Apeks HP seat (1st stage)
AP1154 010 1/16 1/4 Low-Pressure Hose/2nd Stage Regulator
Cylinder Valve Stem
Apeks crown (2nd stage)
AP1409 011 1/16 5/16 Standard Low-Pressure Port/Hose (3/8 UNF)
Apeks adjusting screw (2nd stage)
Apeks conical filter (1st Stage)
Apeks FSR HP crown (1st stage)
Power Inflator quick disconnect oring
AP1445 012 1/16 3/8 High-Pressure Port/Hose (7/16 UNF)
Manifold and Manifold Port Plugs
AP1410 013 1/16 7/16 Large Low-Pressure Port/Hose (1/2 UNF)
Apeks balance plug inner (1st stage)
AP1159 014 1/16 1/2 Standard Yoke Regulator/K-valve
Apeks ATX adjuster screw (2nd stage)
AP1267 015 1/16 9/16 Apeks value spindle (2nd stage)
Cylinder Valve Bonnet Nut
AP1438 019 1/16 13/16 Apeks Venturi (2nd stage)
Apeks turret bolt (1st stage)
AP1420 024 1/16 1-1/8 Apeks Turret (1st stage)
AP1166 111 3/32 7/16 Apeks DIN Regulator/Valve
Apeks Yoke spare (2nd stage)
Note: Yoke valves often use BS112 or BS014
- 214 1/8 1 Cylinder with Large Neck/Valve
(3/4 NPS - All Aluminum, most Steel cylinders)
AP2041 2x1
(606)
1mm 2mm Apeks shuttle valve (2nd stage)
AP5711 2.5x1
(607)
1mm 2.5mm Apeks ATX adjuster screw nib (2nd stage)
AP1300 15x1.5 1.5mm 15mm Apeks HP balance plug outer (1st stage)
- 006 2.9mm 1.78mm Power Inflator spindle (Polyurethane)
- 012 1/16 3/8 Power Inflator cylinder inner oring (Buna)
- 112 3/32 1/2 Power Inflator cylinder outer oring (Buna)
- 204 1/8 3/8 Power Inflator oral inflate oring (Buna)

 
Please download/view the Apeks Spare Parts and O-Ring Identification Chart (Adobe PDF | 308.83 KB).

Scubapro O-Rings

Please download/view the Scubapro O-Rings Chart (Adobe PDF | 59.32 KB).

Tech Tip:
SCUBA Regulator DIN Connector O-ring Sizes

The ISO 12209 standard specification for dimensions of the O-ring groove in the nose of the 232 bar and 300 bar DIN connectors for compressed air has an inside dimension of 12 mm and an outside dimension of 17 mm. In 2003, the standard depth for the groove was revised from the original 1.9 mm to a slightly deeper 2 mm. The specification for the sealing O-ring itself is an inside diameter of 11.2 mm with a cross section of 2.65 mm. From what we have been able to determine, not all SCUBA regulator manufacturers seem to use the current standard groove and O-ring in the universal DIN fittings found on their first stages.

The sealing O-ring in the nose of the DIN connector groove we find on most SCUBA regulator first stages is commonly an SAE AS568 and BS ISO 3601 imperial standard 112 size that is equivalent to 12.37 X 2.62 metric dimensions. In the case of a few regulators (notably Apeks, Atomic, and ScubaPro brands) their groove better accepts the next smaller 111 size O-ring that is equivalent to 10.77 X 2.62 metric dimensions. Both the 112 and 111 size O-rings are very common sizes available in a variety of choices for material and durometer.

The groove in the Cressi and Poseidon brand regulator DIN connectors measures closest to the original standard, best accepting a BS ISO 3601 metric size O-ring with 11.3 X 2.4 dimensions for which there is no imperial standard equivalent. The M2.4X11.3 size O-ring is uncommon, especially in a material suitable for use with Nitrox. (FYI, the O-ring in Yoke K-valves is easy, it is always an 014 size.)

Compared to the 111 size, the M2.4X11.3 size is slightly smaller cross section and slightly larger diameter with a good fit for the O-ring groove of the DIN connectors on Cressi and Poseidon regulators. Because of availability, most Nitrox and technical divers make do with a 111 size O-ring for their Cressi and Poseidon regulators, but the 111 is not as good a fit for the connector of those two brands.

In the European Union nations, the EN 144-3:2003 standard requires a valve outlet known as M26x2 to be used on dive cylinders containing oxygen or Nitrox mixtures with greater than 22% oxygen. The M26x2 outlet is similar in appearance but slightly larger than the standard DIN outlet, and thus incompatible with the standard DIN connector found on SCUBA regulators. The purpose of this incompatible valve outlet is to force the dedication of cylinders, regulators and fill stations to Nitrox use. The sealing O-ring in the nose of the M26x2 connector is 13.9 X 2.6 metric dimensions, equivalent to the 113 size. The M26x2 outlet and connector for Nitrox and oxygen is very rarely seen outside the EU.

O-rings Available from The Scuba Doctor

At The Scuba Doctor Dive Shop we keep the following O-rings commonly used on the face of DIN regulators and cylinder/tank valves in stock for purchase in-store as emergency replacements:

  • N70-112 - Oring Black NBR 70 Duro BS112, 0.487 x 0.103"
    N90-112 - Oring Black NBR 90 Duro BS112, 0.487 x 0.103"
    V75-112 - Oring Brown FPM 75 Duro BS112, 0.487 x 0.103"
    Used as the Standard for most DIN First Stage Regulators, plus most DIN Valve inserts (e.g. those on the Faber/San-o-Sub DIN/K valves).
  • N70-111 - Oring Black NBR 70 Duro BS111, 0.424 x 0.103"
    Used on Small DIN First Stage Regulators (e.g. Apeks and Scubapro), plus some DIN Valve inserts, and Old Yoke Valves
  • N90-110 - Oring Black NBR 90 Duro BS110, 0.362 x 0.103"
  • N90-014 - Oring Black NBR 90 Duro BS014, 0.489 x 0.070"

Sonar DIN O-Rings for Cressi and Poseidon First Stages (10 Pack) Sonar DIN O-Rings for Cressi and Poseidon First Stages (10 Pack)
RRP: $12, Our Price: $9, You Save $3 (25%).
The Sonar DIN O-Rings for Cressi and Poseidon First Stage Regulators are a great save a dive kit item. The O-rings in this pack of 10 are coloured Yellow which makes it easy to identify them.

Sonar DIN O-Rings for Apeks and Scubapro First Stages (10 Pack) Sonar DIN O-Rings for Apeks and Scubapro First Stages (10 Pack)
RRP: $12, Our Price: $9, You Save $3 (25%).
The Sonar DIN O-Rings for Apeks and Scubapro First Stage Regulators are a great save a dive kit item. The O-rings in this pack of 10 are coloured Red which makes it easy to identify them.

Sonar DIN O-Rings for Mares First Stages (10 Pack) Sonar DIN O-Rings for Mares First Stages (10 Pack)
RRP: $12, Our Price: $9, You Save $3 (25%).
The Sonar DIN O-Rings for Mares First Stage Regulators are a great save a dive kit item. The O-rings in this pack of 10 are coloured Blue which makes it easy to identify them.

Sonar Scuba O-Ring - 112 NBR 90 Duro - Black (10 Pack) Sonar Scuba O-Ring - 112 NBR 90 Duro - Black (10 Pack)
RRP: $10, Our Price: $8, You Save $2 (20%).
This is the O-ring size typically used at the front and back of the DIN insert used to convert standard DIN valves to INT/Yoke valves. These are the O-rings we prefer to use on the Faber / San-o-Sub DIN/K valves on Faber steel cylinders. We prefer these harder 90 durometer O-rings over the softer 70 duro ones commonly used.

Sonar Scuba O-Ring - 112 Viton/FPM 75 Duro - Brown (5 Pack) Sonar Scuba O-Ring - 112 Viton/FPM 75 Duro - Brown (5 Pack)
RRP: $15, Our Price: $11.50, You Save $3.50 (23%).
This is the O-ring size typically used at the front and back of the DIN insert used to convert standard DIN valves to INT/Yoke valves. These are the O-rings we prefer to use on the Faber / San-o-Sub DIN/K valves on Faber steel cylinders that are being used for Nitrox or Oxygen.

Trident O-Ring Kit and Pick Trident O-Ring Kit and Pick
RRP: $29, Our Price: $26, You Save $3 (10%).
A mini scuba cylinder/tank container with Brass Pick and 10 popular diver O-Rings. A must for any diver's spares kit!

We have a range of O-Rings and Lubricants available for purchase from our online dive shop.

Scuba O-Ring Application Guide

Products Indicative Application Guide
003 Submersible pressure gauge/consoles: internal swivel seal
004 Older internal swivel seal models; AT-PAC BC's Power inflator control Sherwood 6121-122, Apeks id: AP6403
005 Seal used in older depth and tank stem gauges
006 Common seal in regulator balance chambers; Power inflator stems; CO2 detonators; SAS gland seal. Sherwood 5121-101,6500-118, Scubpro 1.050.117, Mares 46110101, Apeks ID: AP1299
007 Regulator piston ring; small HP seal, Sherwood G007A
008 Sonic regulators; Regulator piston ring; small HP sea, Sherwood 6110-129, Scubapro 1,050,126
009 Seal in open-tube depth gauges, Sherwood 6121-135,6400-113
010 Regulator hose: swivel end; Piston barrel HP seal; 2nd stage orifIce seal; Valve stem seals; Early Calupso Regulators; Power inflators stems; Sherwood 5121-104,6110-119,6161-101,6121-137, Scubapro 1,050,351, Mares 46110107, Apeks ID: AP1154
011 Regulator hose: male end; Regulator port plugs LP; Hose adapters; J-regulators; Early replacement HP seats; Captured HP outlets; Piston HP barrel BC hose coupler, Scubapro 1,050,351, Mares 46110107, Sherwood 5121-103, Apeks: AP1409
012 Console/gauge hoses: male end; Underneath filter; Hose adapters; HP seat seal; LP swivel cap; HP port plugs, Scubapro 1,050,145, Mares 46110108, 46110110, Apeks: AP1445
013 Piston seat seal; Survivair manifolds; Power inflator seals; Common in aluminium cylinder valve to yoke regulator seals Sherwood 6400-115, Scubapro 1,050,147, Mares 46110215, Apeks: AP1410
014 + 2nd stage inlet fittings; J-regulators; Common in aluminium cylinder valve to yoke regulator, Sherwood 5121-105, Scubapro 1,050,347, Mares 46110211, Apeks: AP1159
015 1st stage inlet fittings; HP seal retainer seal; J valve module; Valve HP plugs; 2nd stage barrel and housing plug seals, Shewood 5121-106, Scubapro 1,050,158, Apeks: AP1267
016 Old 1/2-inch NPS valves; 2nd stage inlet fittings; SAS LP seats; J-regulators; HP module seal; Valve HP plugs; 2nd stage barrel and housing plug seals; Paintball Guns; M18X1, 5 Valves, Sherwood 6400-125, 6500-129, Scubapro 1, 050, 160
017 Regulator piston ring and cap; Dacor HP module, Scubapro 1, 050,160, 1,050, 162, Mares 46110225
018 Regulator piston ring (1970's); 2nd stage inlet seal; Body plug seal
019 Healthway / USD / Sherwood industrial piston regulator, Apeks: AP1438
020 Regulator piston ring (USD & SAS) Sherwood 6400-102
021 Regulator piston ring
022 Common regulator piston ring; Body plug seals; Paintball guns, Sherwood 5110-107, Scubapro 1,050,177
023 Regulator LP swivel seal; Body plug seals Sherwood 6110-131,6400-107
024 Piston cap seals (USD); SAS 1st stage Sherwood 6110-125, Apeks: AP1420
025 Gauge lenses, Sherwood 5110-109
026 For Suunto C3, Cobra,EON, VIPER, FAVOUR, AIR LUX Computers
027 Scubapro part no 1,050,164
106 Sherwood part no 5121-102
107 Sherwood part no 6121-129
109 Scubapro part no 1,050,385
110 Old double manifolds; Spearguns
111 Australian / Nemrod valves; BC inflators; DIN regulator seals Sherwood 6400-138, Scubapro 1,050,193;1,050,428, Mares 46110247, Apeks: AP1166
112 Steel tank valve; Basal DIN seal, Scubapro 11,361,115
113 Aquarius piston ring / cap seal; Healthway regulators
114 Early piston models; Paintball Guns
115 AMF HP module; BC fittings
116 Genesis tank valve; BCD Inflator Mechanisms; Paintball Guns
211 Early BC fittings
213 Early BC fittings
214 Cylinder to 3/4-inch valve seal; Cylinder to M25X2 valve Seals
215 Cylinder to M25X2 valve Seals
610 BCD internal hose O-ring clip end
2,4 x 1,9 RO Scubapro part no 1,050,317
24 X 2 For Suunto C6, Zander
36 X1.5 For Suunto C9 and D9
39 X 1 For SUUNTO C1, Stinger, Spider computers
39 X 1.50 For Suunto C8 and D4
15 X 4.00 Mares part no 46200559
902 Scubapro part no 1,050,293
903 Sherwood part no 6121-141
905 Sherwood part no 6400-135
906 Sherwood part no 6110-115 & 6121-104
119 Mares Spear Gun
123
27 x 1,3 For Aeris F10 diving watch
1,7 x 1.0 For Apeks regulators
1.95 X 1.0 Sherwood part no 6500-112
2.20 X 1.0 Scubapro part no 1,050,363
2,5 x 1.0 For Apeks regulators

WARNING:
Designers of modern SCUBA equipment often specify O-rings with special properties and materials for specific uses inside their equipment. The special o-rings are supplied as part of original equipment manufacturer (OEM) service parts kits. Substituting any other generic O-ring just because it's the right size can cause difficult-to-diagnose problems and degrade performance. Improper service could cause a failure which would have serious and life threatening consequences.

The Scuba Doctor Online Dive Shop