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Valve Diaphragms, Seals & Discs – Types & Uses

Many people have been asking which type of diaphragm, seals and discs they should use with their AqMatic/AquaMatic valves, or need replacement parts for a valve they already have.

With a little bit of data we can determine what is the right kit to get.

I hope this helps.

General Uses

Buna-N = Standard operation for most liquids and air.

FKM = For high temperatures.

EPDM = For corrosive liquids.

Hycar = For air and gasses.

BUNA-N DIAPHRAGM, DISC & SEALS

Buna-N is Nitrile synthetic rubber, also known as Perbunan, acrylonitrile butadiene rubber, and NBR.

Buna-N is more oil, fuel and chemical resistant than normal rubber but is less flexible.  It also has a much higher working temperature ranging between −40 to 108 °C (−40 to 226 °F), however, for AqMatic/AquaMatic valves we recommend a maximum of 65°C (150°F) for the Buna-N seals and disc,  and 93°C (200°F) for the diaphragm if used with EPDM or FKM seals and disc.

 

FKM DIAPHRAGM, DISC & SEALS

FKM (by ASTM D1418 standard) (equivalent to FPM by ISO/DIN 1629 standard) is the designation for about 80% of fluoroelastomers as defined in ASTM D-1418.

Fluoroelastomers, while more expensive than Buna-N diaphragms, seals and disc, provide greater heat and chemical resistance.

FKM diaphragm, seals and disc have an operating temperature of 121°C (250°F)

 

EPDM DISC & SEALS

EPDM is a synthetic rubber conforming to ASTM D-1418.

The main properties of EPDM are its outstanding heat, ozone, and weather resistance. The resistance to polar substances and steam are also good.

It has good resistance to ketones, ordinary diluted acids, and alkalies.

EPDM exhibits satisfactory compatibility with fireproof hydraulic fluids, ketones, hot and cold water, and alkalis and exhibits unsatisfactory compatibility with most oils, gasoline, kerosene, aromatic and aliphatic hydrocarbons, halogenated solvents, and concentrated acids.

 

HYCAR DISCS

Hycar-OR is an oil-resistant synthetic rubber produced and sold by the Hydrocarbon Chemical and Rubber Company.

It is a nitrile rubber that has add carboxyl added in production.  This creates a higher oil, solvent, abrasion and heat resistance and lower gas permeability.

The Hycar operating temperature is only limited by the diaphragms and seals used with it.

Because of this, Hycar discs are used on all AqMatic/AquaMatic Air Diaphragm Valves and are provided as an option for the V42 Metal Diaphragm Valves.

 

References

Buna-N : https://en.wikipedia.org/wiki/Nitrile_rubber
FKM: https://en.wikipedia.org/wiki/FKM
EPDM: https://en.wikipedia.org/wiki/EPDM_rubber
Hycar: http://pubs.acs.org/doi/abs/10.1021/i460004a026

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