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Apeks O-rings

posted Mar 4, 2012, 12:05 AM by Derek Quek

This article 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

Only o-ring are listed here. Additional parts such as diaphrams and seats are not listed here.


There are several common materials used for SCUBA o-rings.

Acrylonitrile-Butadine Copolymers
(NBR, Nitrile or Bunan) 'N'
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 or Viton Fluorel) 'V'
O-rings made of FKM are more costly but are a 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 Dow's brand name for FKM. FKM has a higher heat tolerance, but emits a highly toxic gas if combusted.
Ethylene Propylene Diene Monomer
(EPDM) 'E'
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. EPDM is not recommended for use with petroleum derivatives.

Starting from 2001, Apeks o-rings are based on EPDM with a hardness rating of 80 Shore-A.


Most scuba o-rings are based on imperial British Standards (BS) using a three-digit identifier. The first digit denotes the O-ring cross section width: 0xx = 1/16-inch, 1xx = 3/32-inch, 2xx = 1/8-inch. The other 2 digits are used to reference the diameter of the o-ring.

Apeks IDBSCross SectionInner diam.SCUBA Application Seal
-0031/161/16High-Pressure Hose/SPG swivel
AP64030041/165/64High-Pressure Hose/SPG swivel (less common)
AP12990061/161/8Apeks HP seat (1st stage)
AP11540101/161/4Low-Pressure Hose/2nd Stage Regulator
Cylinder Valve Stem
Apeks crown (2nd stage)
AP14090111/165/16Standard 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
AP14450121/163/8High-Pressure Port/Hose (7/16 UNF)
Manifold and Manifold Port Plugs
AP14100131/167/16Large Low-Pressure Port/Hose (1/2 UNF)
Apeks balance plug inner (1st stage)
AP11590141/161/2Standard Yoke Regulator/K-valve
Apeks ATX adjuster screw (2nd stage)
AP12670151/169/16Apeks value spindle (2nd stage)
Cylinder Valve Bonnet Nut
AP14380191/1613/16Apeks Venturi (2nd stage)
Apeks turret bolt (1st stage)
AP14200241/161-1/8Apeks Turret (1st stage)
AP11661113/327/16Apeks DIN Regulator/Valve
Apeks Yoke spare (2nd stage)
Note:Yoke valves often use BS112 or BS014
-2141/81Cylinder with Large Neck/Valve
(3/4 NPS - All Aluminum, most Steel cylinders)
AP20412x1(606)1mm2mmApeks shuttle valve (2nd stage)
AP57112.5x1 (607)1mm2.5mmApeks ATX adjuster screw nib (2nd stage)
AP130015x1.51.5mm15mmApeks HP balance plug outer (1st stage)
-0062.9mm1.78mmPower Inflator spindle (Polyurethane)
-0121/163/8Power Inflator cylinder inner oring (Buna)
-1123/321/2Power Inflator cylinder outer oring (Buna)
-2041/83/8Power Inflator oral inflate oring (Buna)
Adjustments, servicing, disassembly and assembly of scuba equipment should be performed only by individuals who have attained appropriate training and certification by the equipment manufacturer.