Seals, Actuated, Air, Diaphragm, Pump, Valve, O Ring, Compressor, Seal, Viton, High Pressure, Actuator


Composite Diaphragms, High Strength Seal, Inserted Diaphragms, Pneumatic Actuated Diaphragm Valves, Top Hat Diaphragms

Dia•Com Diaphragm Glossary


Hardware | Diaphragm Definition | Diaphragm Function | Diaphragm Design Formulas | Diaphragm Strokes


Convolution Width

Diagram of diaphragm cut-away, showing piston diameter and placement of DiaCom's elastomer and fabric solution.

The clearance between the cylinder wall and piston skirt. By decreasing the convolution width, higher working pressures may be achieved. Generally, the convolution width should measure at least four times the diaphragm's sidewall thickness.


Cylinder Diameter (Bore)

The inside diameter of the cylinder into which the diaphragm will fit and by which the outside diameter of the convolution will be supported.

Cylinder Radius

The blend radius between the cylinder wall and the flange.

Piston Cap

A plate which attaches to the piston, sandwiching the piston area of the diaphragm insuring the diaphragm stays in convolution.

Piston Diameter

Diameter of the piston measured across piston head, including radius.

Piston Radius

The blending radius between the piston head and the piston skirt.

Piston Skirt

The sidewall area of the piston which supports the inside diameter of the convolution.

Diaphragm Definition

Cylinder Diameter

Graphic showing diaphragms being used within a cylinder using cut-aways

The diameter across the diaphragm between the tangent points of the sidewall and cylinder radius.

Fabric Side

Surface of single coat diaphragm where fabric is visible. Always on low pressure side, generally on outside of diaphragm.


The height of top hat and preconvoluted diaphragm is measured from the bottom of the flange to the top of the head or convolution.

Piston Diameter

The diameter across the diaphragm between the tangent points of the sidewall and piston radius. Measured on the fabric or low pressure side of the diaphragm.


A diaphragm which has its convolution molded in. No hand forming is necessary before installation.


That area of the diaphragm between the flange and piston areas.

Top Hat

A diaphragm molded in standard "hat" shape that must be formed into convolution before installation.


Diaphragm Function


A defect in a diaphragm caused during manufacturing where the fabric is pulled through the rubber to the high pressure side of the diaphragm. When pressure is put on the diaphragm, the rubber will be blown away from the fabric and rupture.


This occurs when the pressure on the diaphragm reaches a level high enough to blow a piece of the rubber through the threads of the fabric, causing a leak. This is the result of selecting a weave of fabric that is too open for the diaphragm's thickness.

Double Coat

This is a type of diaphragm construction where the fabric is inserted between two layers of rubber.

Effective Pressure Area

The area of the diaphragm inside an imaginary circle to the convolution midpoint on which the pressure introduced is transmitted to the opposite side of the diaphragm.


Exceeding the designed stroke of the diaphragm causing it to come out of convolution. This can be avoided by designing mechanical stops into your hardware.

Reverse Pressure

When the pressure on the low pressure side of the diaphragm exceeds the pressure on the high pressure side of the diaphragm. This will cause the convolution to collapse and wrinkle. This wrinkle will cause scrubbing and lead to premature failure.

Single Coat

This is a type of diaphragm construction where there is rubber in the high pressure side and fabric on the low presure side.

Spring Rate

This refers to the forces caused by the rubber trying to return to its as-molded position. This is generally found only in preconvoluted and dish-shaped diaphragms.


This refers to the amount of rubber that comes through the fabric to either fully or partially encapsulate the fabric during manufacturing.

Diaphragm Design Formulas


Burst Pressure (PSI) =

Fabric Tensile Strength x 2


Convolution Width




Effective Pressure Area =

Pi( Piston Diameter + Cylinder Diameter )2





Fabric Tensile Required =

Convolution Width x Burst Pressure






Half-Stroke (Preconvoluted) = 2 x Height - [2(Flange Radius) + Convolution Width]

Half-Stroke (Top Hat) = Height - [Flange Gauge + 2(Flange Radius) + 1.56(Convolution Width) + Safety Factor* ]

Height (Preconvoluted) = 1/2 [Convolution Width + 2(Flange Radius) + Flange Gauge + Half Stroke]

Piston Skirt Length =

Height + Half-Stroke




Safe Working Pressure (PSI) =

Burst Pressure







Inches mm Inches mm Inches mm Inches mm

Cylinder Diameter









*Safety Factor









Diaphragm Strokes

Animation showing diaphragm strokes.







Dia•Com is a leading international provider of innovative, cost-effective molded diaphragm solutions critical to the operation of essential systems and equipment in industrial, automotive, aerospace, medical instrumentation, and food and water processing applications. The company's reputation for excellence is based on superior quality in the design, manufacture and application of its high-performance, state-of-the-art, fabric-reinforced and homogeneous elastomeric rubber seals. Our custom engineered solutions are found in many products today, including diaphragm pumps, rubber seals, pneumatic diaphragm pumps, high pressure diaphragm pumps, viton gaskets, diaphragm carburetor, diaphragm pressure gauges, diaphragm vacuum pumps, diaphragm air compressors, diaphgram fuel pumps and diaphragm metering pumps.


home | diaphragm products | elastomer & fabric diaphragm data | diaphragm engineering | diaphragm markets
diaphragm software | about | quality | download catalog | news & events | contact | diaphragm glossary | inquiry | sitemap

Diagram of Seals, Actuated, Air, Diaphragm, Pump, Valve, O Ring, Compressor, Seal, Viton, High Pressure, Actuator, Rubber Seal, Diaphragm Pumps, Diaphragm Valve, Fluorosilicone, Rubber Seals.
web page design