Diaphragm Materials & Construction

Molded diaphragms are composed of tough, flexible, carefully engineered laminates made up of elastomers and fabrics. The elastomer component is one or two pressure-tight layers of tough elastomeric (synthetic rubber) material selected (or specially compounded) for long life under a specific set of operations (fluid type, temperatures, etc). Depending on the application, the elastomer is bonded to one or both sides of a fabric base. The fabric is a high tensile strength base layer of specially woven material designed to withstand the stresses induced by high pressures. Diapgragm construction may also include an aluminum or plastic insert to serve as a valve seat. In some cases, a Telflon layer is added to improve resistance to harsh chemicals and abrasion.

Elastomers / Compounds

The elastomer layer must be extremely thin (for maximum flexibility), very tough (to withstand repeated flexing over a long lifetime), able to handle anticipated operating temperatures, and resistant to whatever chemicals, fluids or gases it may be contacting.

A number of standard elastomers are available, one of which usually meets the application requirements. RPP material specialists also work closely with our synthetic rubber compounders to develop custom materials to meet specific customer needs.RPP’s new proprietary EPDM elastomer comes in three colors, white, purple and standard black. Its high degree of inertness and robust physical properties makes it ideal for harsh water environments with high chloromine & chlorine levels. A new low cost Type A FKM is a popular choice for the toughest chemical applications.The following elastomers are typical of those frequently used in molded diaphragm construction.The elastomers listed in the table below are typical of those frequently used in molded diaphrams contruction. RPP utilizes over standard and counstom compounds base on these elastomers additionally, because RPP manufactures it's own coated fabrics, diaphragms can be produced with almost any combination of elastomers and fabrics. RPP can even produce coated fabric with different elastomer on each side of the fabric.


RPP Utilizes over 40 Standard and Custom Compounds Based on These Elastomers

Elastomer Temperature Range Air
Permeability
Generally Resistant To.. Generally Attacked By...
Nitrile (NBR)
-40F to 250F
-40C to 121C
0.80
Petroleum-Based Oils
Esters and Chlorinated Solvents
                                                                                                                                                                                                                                   ____
Neoprene (CR)
-25F to 250F
-32C to 121C
1.40
Weather and Ozone
Esters and Chlorinated Solvents
____                                                                                                                                                                                                                                   
Ethylene Propylene EPDM)
-40F to 300F
-40C to 149C
10.00
Weather and Ozone
Aromatic Hydrocarbons
____                                                                                                                                                                                                                                   
Epichlorohydrin (CO/ECO)
-20F to 300F
-29C to 149C
0.40
Petroleum-Based Oils
Esters and Chlorinated Solvents
                                                                                                                                                                                                                                   ____
Silicone (SI)
-85F to 500F
-65C to 260C
175.00
Weather and Ozone
Gasoline and Chlorinated Solvents
                                                                                                                                                                                                                                ____   
Fluorosilicone
(FSI)
-85F to 450F
-65C to 232C
85.00
Petroleum-Based Oils and Ozone
Ketones and some Hydraulic Fluids
                                                                                                                                                                                                                                    ____
Fluorocarbon
(FKM) (Viton)
10F to 550F
-12C to 288C
0.30
Gasoline and Chlorinated Solvents
Ketones and some Esters
                                                                                                                                                                                                                                   ____
Polyacrylate (ACM)
-20F to 350F
-29C to 177C
1.50
Hot Oil, Ozone Pentroleum Solvents
Water, Esters and Aromatic Hydrocarbons
                                                                                                                                                                                                                                  ____ 
Polyruethane (PUR)
-40F to 250F
-40C to 121C
0.40
Goog Abrasion & Ozone Resistance
Acids, Ketones, esters Chlorinated & Nitro hydrocarbons
                                                                                                                                                                                                                                ____   

Note:  RPP Corporation also has several specialty compounds for applications requiring AFLAS, Saturated Nitrile, and low cost nitriles, silicones and fluoro carbons

 

Diaphragm Seal Fabrics

The fabric used in molded diaphragms employs a specially developed weave pattern with a unique property. 

In one direction, it stretches easily, allowing for the radial flexing of the diaphragm convolution.  In the other (axial) direction, it provides high resistance to elongation and furnishes the tensile strength that enables the seal to withstand high differential pressures and transmit force to the piston head. 

A variety of diaphragm fabrics, woven specially for RPP, are available.  RPP has developed over 20 unique varieties of fabric designed to meet specific operating conditions. Special, low cost knit versions are also available for high volume and low hysteresis (for more sensitive applications).

 

Fabric Type Maximum 
Temperaturee
Typical Usage
Polyester
325F / 163C
Generally used for single-coated diaphragms Medium to high strength
                                                                                                                                                                                                                                   
Polyamide
275F / 135C
Generally used for double-coated diaphragms High Strength
                                                                                                                                                                                                                                   
High-Temp Polyamide / Meta-Aramid
500F / 260C
Used in high-temperature, single and double-coated applications. Medium to high strength
                                                                                                                                                                                                                                   
Liquid Crystal 
Polymer based fabrics
500F / 260C
High temperature,extremely high tensile strength application.
                                                                                                                                                                                                                                   

RPP Engineers have developed less costly material equivalents for high temperature / high strength fabrics such as Nomex® and Vectran®

Document Download files

 

Elastomer and Media Compatibility Chart (2,000KB PDF)   RPP Elastomer Physical Properties (795KB PDF)