Diaphragm Design Guidebook

DIA·COM CORPORATION
The Diaphragm Company
Online Guidebook: www.diacom.com

603.880.1900
 DIA·COM CORPORATION
The Diaphragm Company 603.880.1900 · www.diacom.com

Providing Superior Solutions to Tough Sealing Problems in:

Automotive

Natural Gas

Aerospace
Industrial

Medical

Consumer
Products
Water Control
Irrigation
Food
Processing
The information contained herein is believed to be reliable, but no representations, guarantees or warranties of any kind are made as to its accuracy, suitability for
particular applications or the results to be obtained therefrom. Nothing contained herein is to be considered as permission, recommendation, nor as an inducement to
practice any patented invention without permission of the patent owner.

2 © 2018 DiaCom Corporation

 Why Choose DiaCom Corporation?
Since its founding in 1983, DiaCom has been committed to 2015 and ISO 9001 certification in 2016. We are constantly
a single goal: the design and production of the finest molded striving for continuous improvement. The AS-9100 standard
diaphragm seals available. Today, DiaCom is an industry- implements a strong focus on product quality, process control,
leading provider of innovative, cost-effective molded diaphragm and product conformity to specification. By encompassing our
solutions that are critical to the operation of essential equipment Engineering expertise and advanced manufacturing capabilities,
and systems in: Industrial, Automotive, Aerospace, Medical DiaCom is able to deliver engineered diaphragm solutions
Instrumentation, Food and Water processing, and Gas that are unsurpassed in performance. DiaCom uses our core
Regulator/Gas Metering Applications. Our reputation for expertise of bonding industrial fabrics, fluorinated films, plastics
solving the toughest sealing problems is based on our superior and metals to our custom engineered elastomers in a variety of
quality management system, our engineering expertise, and molded parts including: fabric reinforced diaphragms, molded
advanced manufacturing capabilities. DiaCom’s commitment diaphragms, rolling diaphragms, diaphragm seals, chemical
to quality is reflected in our latest AS9100 Certification in septums, bellows, accumulators, valve plungers and valve seats.

Molded Diaphragms - Ideal Solutions to Tough Sealing Problems

The molded elastomeric diaphragm is a tough, versatile, These molded diaphragm features ensure unmatched
dynamic seal that eliminates virtually all of the problems performance:
and limitations associated with other sealing methods
• Minimum hysteresis – accurate, repeatable positioning
such as U-Cups, O-Rings, metal bellows and flat,
die-cut diaphragms. Unlike alternative techniques, • No spring rate (rolling diaphragms)
molded diaphragms do not leak, offer no friction, have • Long stroke length capabilities
exceptional sensitivity, and display a hysteresis that is, in
most cases, negligible. They can withstand pressures up • No lubrication
to 6000 PSI over a temperature range of -65°F to 600°F, • No break-away or sliding friction
require no maintenance or lubrication, and are extremely
cost-effective in most applications. DiaCom molded • Long cycle life
diaphragms are available in two forms: contoured, annular • Effective in harsh environments
disks that provide high sensitivity and freedom of motion
in short-stroke applications, and rolling diaphragms for • Constant effective pressure area
frictionless, leak-proof sealing in cylinders and other • Low assembly and associated hardware costs
applications requiring a long piston stroke.

Table of Contents
DiaCom Rolling Diaphragm Theory...................................................................................................................................................4
Glossary of Terms ............................................................................................................................................................................5,6
Diaphragm Design Formulas .............................................................................................................................................................6
General Hardware Information ....................................................................................................................................................7,8,9
Rubber To Metal Bonding ..................................................................................................................................................................9
PTFE/Elastomeric Diaphragm Seals ................................................................................................................................................9
Diaphragm Life Design Considerations ......................................................................................................................................10,11
Bead and Groove Design Considerations .....................................................................................................................................12,13
Type F Diaphragms ......................................................................................................................................................................14,15
Type FC Diaphragms & FC Offset Diaphragms...........................................................................................................................16,17
Type D Diaphragms .....................................................................................................................................................................18,19
Type DC Diaphragms .......................................................................................................................................................................20
Type OA and O Diaphragms ............................................................................................................................................................21
Type OB Diaphragms .......................................................................................................................................................................22
Type P Diaphragms...........................................................................................................................................................................23
Typical Fabric Characteristics ..........................................................................................................................................................24
Chemical Compatibility Table...........................................................................................................................................................25
Application Data Form......................................................................................................................................................................26
The DiaCom Advantage....................................................................................................................................................................27
© 2018 DiaCom Corporation 3
 DiaCom Rolling Diaphragm Theory

Theory:
Figure 1 illustrates pressure reaction on the diaphragm. It can be seen that Where Ft is the tension force on the diaphragm sidewall for each unit of
almost the entire pressure load is supported by the piston head, and only circumferential length. Since tensile force Ft and fabric stress Sf are identical,
a small amount of the liquid or gas pressure is supported by the narrow equation 4 can be expressed in terms of fabric stress:
convolution of the diaphragm. Also note in Figure 1 that the lines of unit
pressure (acting in horizontal planes because they must be normal to the 5. Sf = Pr x C where
surface) force the diaphragm against the piston and cylinder sidewalls on that 2
portion of the diaphragm in contact with the cylinder wall and piston skirt. Sf = fabric stress (lbs. per inch)
The lines of force acting on that part of the diaphragm not in contact with Pr = normal loading or applied pressure (psi)
the cylinder or piston skirt (the semicircular segment of the convolution) C = convolution width (inches)
are shown in Figure 2. Each line of unit pressure (Pr) acts normal to the
semicircular segment; thus any one of the pressure lines can be replaced by Fabric stress can be computed using equation 5. For example,
its horizontal and vertical component. The horizontal components, acting in if a 3-inch diameter diaphragm with an effective pressure area
opposition, cancel out each other. of 6.35 sq. in. and a convolution width of .156 is subjected to a
loading pressure of 100 psi, the resulting total thrust is 635 lbs.
However, fabric stress on the narrow convolution is only:

6. Sf = 100 x .156 = 7.8 lbs. per inch

2

Fabric materials are available in tensile strengths greater than 7.8 lbs.
per inch. Therfore the very narrow convolution widths with resulting
low stress values in the fabric fibers enable diaphragms to be used
in applications involving high working pressures. In effect, DiaCom
Rolling Diaphragms are pressure vessels having a variable volume

Figure 1
The sum of the vertical components of the unit pressures acting on this
semicircular segment add up to the total pressure force (F) and is equal to
the normal pressure on the projection of this segment.

Considering a unit (1 inch) of circumferential length of the diaphragm, the

foregoing is:

1. F = Pr x 1 x C or F = Pr x C where
F = total pressure force (lbs.)
Pr = normal loading or applied pressure (psi)
C = convolution width (inches)
Figure 2
The total force F is supported equally by the fabric reinforcement of the
diaphragm on the piston and cylinder wall (See figure 2). Therefore tension
force, Ft (lbs.), in either wall is simply one-half the value of F or and flexible moving sidewalls. As in any other pressure vessel, its
strength should be considered with respect to safety factors. Generally,
2. 2Ft = F or Ft = F diaphragms can be designed with a large safety factor. In effect, this
2 means the maximum safe working pressure will be a fraction of the
pressure that would cause failure in the convolution area. (In some
However, as aircraft applications where working pressures are as high as 1000 psi,
and total cycle requirements are low, safety factors are substantially
3. F = Pr x C then
increased.) Actual stress analysis and selection of fabrics will be
recommended by the DiaCom engineering department for each
4. Ft = Pr x C
application.
2

4 © 2018 DiaCom Corporation

 Glossary of Termsll

Hardware:
Convolution Width – 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. (See page 6 for standard convolution widths.)

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:
Cylinder Diameter – The diameter across the diaphragm
between the tangent points of the sidewall and cylinder radius.
Measured on the fabric or low pressure side of the diaphragm.

Fabric Side – Surface of single coat diaphragm where fabric

is visible. Always on low pressure side, generally on outside of
diaphragm.

Height – 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

Top Hat Diaphragm
the tangent points of the sidewall and piston radius. Measured
on the fabric or low pressure side of the diaphragm.

Preconvoluted – A diaphragm which has its convolution

molded in. No hand forming is necessary before installation.

Sidewall – 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 Preconvoluted Diaphragm

© 2018 DiaCom Corporation 5

Glossary of Terms (continued)

Bleed-through – 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.

Blow-through – 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 of an imaginary circle to the convolution midpoint on which
the pressure introduced is transmitted to the opposite side of the diaphragm.

Over-stroke – 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 on the high pressure side and fabric on the
low pressure side.

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

Strike-through – 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:

(Note: Please See Page 22 for Fabric Tensile Strength)

Cylinder Diameter .33 - .99 8.38 -25.15 1.0 - 2.5 24.50 - 63.50 2.51 - 4.00 63.75 - 101.60 4.01 - 8.00 203.20
* Safety Factor .60 1.52 .100 2.54 .120 3.05 .140 3.56

6 Millimeters in Red © 2018 DiaCom Corporation

 General Hardware Informationl

Diaphragm Strokes:

Down-Stroke Position Neutral Plane Position Up-Stroke Position

Piston and Standard Convolution Width Dimensions:

0.80

Piston Cap Dimensions:

Note: A piston cap is recommended for ALL applications. Required for fast cycle rates, long stroke and high pressure applications.

Bonnet Dimensions: Cylinder Dimensions:

© 2018 DiaCom Corporation Millimeters in Red 7

 General Hardware Information

Flange Retention Methods for Type F and FC Diaphragms:

Most common flange retention method. Lending itself to high volume/low cost, This method lends itself to high volume and
Bolt holes should be at least 15% larger the swaged lip resembles the crimp ring low cost manufacture. It utilizes a separate
than the bolt. Allow sufficient number in design except that the lip is an integral metal crimp ring and is assembled to unit
of bolt holes to eliminate bowing or part of the cylinder or bonnet. Lip should with special crimping tools. These crimp
distortion of flange, providing a tight seal be flexible and thin to insure proper flange rings are made of thin, ductile materials so
and preventing the diaphragm flange from retention that the force required to form the lip will not
pulling out between the bolts. over-compress the diaphragm flange area.

Flange Retention Methods for Type D and DC Diaphragms:

Provides quick assembly and disassembly. “V” style clamp rings can be disassembled Eliminates the need for flange bolts as a
The pivoted rocking bracket is attached quickly by removing a clamp lever. A beveled edge ring is snapped into a groove
to the housing flange and the central jam retainer plate is removed by turning it 90 in the extension of the cylinder housing
screw secures the bonnet against the mat- degrees where two“wings” and a retaining flange. This loads the bonnet assembly
ing flange. screw drop into a keyhole. onto the mating bead, generally producing
low clamping forces.

Flange Retention Methods for Type O and OA Diaphragms:

Used in high volume, low cost applications, This common method provides minimum This method requires sufficient number of
this method eliminates typical flange con- clearance of the housing outside diameter. circumferential clamp bolts so distortion
struction and flange bolts. Male threads are machined on the cast does not occur between flange bolts. It is
bonnet to utilize drawn sheet metal cylinder advisable to make provisions for the bead
housings, reducing costs. groove in the cast or molded bonnet.

8 © 2018 DiaCom Corporation

 General Hardware Information

Rubber to Metal Bonding:

DiaCom has capabilities to bond metal or plastics to diaphragms during
the molding process. Mechanical bonding is generally the least expensive
and simplest method to achieve. This process is accomplished by designing
the insert with projections or holes. During the molding process the insert
becomes totally or partially encapsulated by the elastomer creating a strong
mechanical interlock. Figure 1 illustrates a mechanical bond.

Chemical or adhesive bonding utilizes a commercial adhesive applied to

the non-elastomeric component. The component is then attached to the
elastomer during or after vulcanization depending on the type of bond
required and geometry of the diaphragm. Figure 2 illustrates an adhesive
bond.

When designing the metal insert it is recommended to avoid sharp

projections extending into the elastomer or sharp corners at the junction
line between the two materials.
Figure 1
Steel is the most prevalent insert material used but brass, stainless steel,
aluminum, and nylon are also used. Certain elastomers and insert materials
can also develop a cohesive bond through molecular attraction. This is
most commonly accomplished with the use of brass and a sulfur-cured
nitrile.

By bonding inserts to diaphragms, costly assembly operations can be

reduced or eliminated. Additionally, rivet, screw or other fastening
methods which might create leak-paths through the diaphragm would be
eliminated with a bonded insert.
PTFE/Elastomeric Seals:
DiaCom has capabilities to design and manufacture that is compatible with these harsh environments without
composite diaphragms made from PTFE/ limiting the life and responsiveness of the diaphragm. For
Elastomeric materials capable of standing up to even the additional strength, fabric reinforcement may be added
most chemically agressive of environments. DiaCom’s to the PTFE/Elastomer composite. Bonded inserts of
process bonds PTFE, ranging in thickness from .002” up stainless steel, brass, plastic, and cold-rolled steel are often
to .040”, to rubbers of varying characteristics. DiaCom’s incorporated into these diaphragms to reduce process/
unique process and construction produces a diaphragm assembly steps and add value.

PTFE

Benefits of PTFE/Elastomeric Diaphragms include:

• Excellent Chemical Resistance • Low Permeation Rate

• Temperature Extremes (–45° to 400° F) • Low Co-Efficient of Friction

• FDA Approved Materials

© 2018 DiaCom Corporation 9
 Diaphragm Life Design Considerations
When designing a diaphragm a prime consideration is what
can be done to extend the life of the part. The factors that
contribute the most to early failure of a diaphragm are; sharp
edges, abrasion, back pressure, and circumferential
compression. The first step is in the hardware design itself.

The obvious considerations are the elimination of burrs and

sharp edges that may come in contact with the diaphragm.
These flaws will cut and tear at both fabric and elastomer
resulting in premature failure.
Reverse Pressure
Not so obvious is the finish of the hardware. When pressure
The second cause of this type of failure is back-pressure.
is constantly applied then relieved the diaphragm does
Generally, diaphragms can only take a high differential in one
rub against the supporting hardware. If the surface of the
direction If the pressure gets higher on the low pressure side
hardware is rough it can abrade the fabric causing an earlier
of the diaphragm the sidewall collapses causing failure. The
than expected failure. It is recommended that these surfaces be
problems with back-pressure usually occur when the user is
no rougher than 32 micro inches and if necessary be finished
unaware that it even exists. Since most diaphragm applications
to 16 micro inches in higher cycle applications. Although
are in closed actuators there must be a means to adjust for the
change in gas or fluid volume above and below the diaphragm as it
is stroked up and down. This is usually not a problem on the high
pressure side of the diaphragm since the change in volume here
is what is counted on for the apparatus to operate and perform
its function. The problem occurs on the low pressure side where
the volume of gas or fluid must be removed and replaced with
each stroke of the diaphragm. Vent holes must be sized correctly
to allow enough volume to pass through in the amount of time it
takes to stroke the diaphragm. It is also important to remember
this when actuation sequences are increased during accelerated
testing or simply faster cycling of your device.
Cocked Piston

diaphragms do not require lubrication they may be coated

with a molybdenum disulfide prior to installation to aid in the
reduction of abrasive wear. The piston may also be coated with
PTFE to reduce friction when the diaphragm shifts against it,
or with an elastomer coating which will prevent the diaphragm
from shifting resulting in the elimination of abrasion.

The quickest failure occurs when the sidewall of the diaphragm

comes in contact with itself. When this happens the two
rubber surfaces lock together while the piston continues to
Over Clamping
travel. This generally results in the sidewall of the diaphragm
being jammed between the piston and cylinder wall with the
Another cause of failure is over-clamping the diaphragm
elastomer and fabric torn. There are generally two causes for
in the hardware during assembly. For the diaphragm to seal
this. The first is the alignment between the piston and
properly, compression of the diaphragm material is expected
cylinder. There is usually no problem at high pressure where
and required. Care must be taken, however, as rubber material
the pressure itself equalizes on the diaphragm helping to center
will act as an incompressible fluid and your design must allow
the piston. However, at low pressure gravity can take over and
for this condition. With proper diaphragm design and assembly
pull the piston to one side causing a problem. This can be
techniques, this condition is not a concern. If over-clamping
avoided with a bushing for the piston or some other way of
exists, the rubber material may bulge into the working area of
keeping the piston centered throughout its stroke.
the diaphragm, precipitating early diaphragm failure.
10 © 2018 DiaCom Corporation
 Observing prudent guidelines can greatly extend service cyclesl
The final cause of failure is circumferential compression. There are several ways to reduce this circumferential
This is a term used to describe the larger diameter sections of compression. The first, is to only use the bottom half of the
the diaphragm sidewall being compressed around the piston. diaphragm’s stroke. Using the bottom half of the stroke limits
As seen in the diaphragm sketches below, a ring section of the section of the sidewall that must be compressed around
material in view A is larger in diameter than the same ring the piston to the top. This is the section of the sidewall with
section in view B. In view A, the diaphragm is rolling onto the the smallest circumference difference with the piston which
cylinder wall while in view B, the diaphragm is rolling onto the means the folds will be smaller and not as sharp. The result
piston skirt. It appears that the ring of material is smaller when of this is longer diaphragm life.
the diaphragm is rolling onto the piston skirt.
Another way to accomplish this and still keep the total
stroke capability of the diaphragm, is the double-tapered
A. diaphragm. On a standard top hat diaphragm, the
sidewall of the diaphragm is a straight line tangent
to the flange and piston radii. On a double tapered
top hat, the sidewall is a line tangent to the cylinder
radius running at a 45 to 60 degree angle to a point
B. approximately 60% of the way through the convolution
width. At this point, it wraps around a small radius
then straight to a point tangent to the piston radius.
This makes the sidewall a much steeper angle for the
usable length of the sidewall which in turn reduces the
circumference. The same effect can also be obtained
by molding the offset into a preconvolulted diaphragm.
In actuality, the ring of material doesn’t vary in size. As the Basically, this is a preconvoluted diaphragm molded
ring of material rolls onto the piston, it forms an axial fold in the full up position. This puts the total amount of
in the sidewall, allowing the diaphragm to conform to the working sidewall at the piston circumference virtually
piston. Because the fabric used for support has a square eliminating circumferential compression.
pattern the folds occur at the four points that the warp
and fill threads are perpendicular to the convolution. This
condition can be seen in the sketch below which shows a
top view of the ring of material when the diaphragm has
rolled onto the piston. This condition is most often referred
to as “four-cornering”, and is not something that can be
eliminated but rather controlled. The continuous folding
at the same location eventually leads to a break in a cross
thread, ultimately leading to a rupture of the elastomer.

Double-Tapered Diaphragm

The final means of reducing the circumferential

compression is with a tapered piston. This simply
increases the piston circumference as the sidewall
circumference increases. This is probably the least
desirable means to solving the problem because while
adjusting the circumference helps it also decreases the
effective pressure as the pressure decreases and tightens
the convolution width as the pressure increases. Both
of these effects must be considered and tested before
Four -Cornering
this solution is used.
© 2018 DiaCom Corporation 11
 Bead Design Considerations

A simple and effective solution, but fit must be precise

One of the most popular flange designs in diaphragms is the Beaded Figure 2
Type. This style of flange enables the designer to control the amount
of squeeze applied to the diaphragm’s flange without concern for the
amount of force applied to the flange during assembly. Controlling
this squeeze avoids the three most common types of premature
failures; 1.) Not enough squeeze resulting in flange leakage, 2.) Over-
squeezing the flange and cutting the diaphragm, or, 3.) Flowing
the elastomer into the working area of the diaphragm causing the
diaphragm to distort and fail prematurely. These benefits can be lost
if the bead and the bead groove are not designed in conjunction with
each other.
Figure 1
Another point to consider when designing beads on diaphragms is
to make them as manufacturable as possible. This will insure a better
product as well as more price stability. The main problem experienced
in the manufacture of beaded diaphragms, is air entrapment. This
“trapped air” displaces elastomer in the bead resulting in a reduction
of bead volume. Generally, air entrapment is not a problem on
standard “D-Bead” parts where the fabric is on the same side of the
part as the bead. The reason for this is that the fabric acts as a leak
path out of the mold for the air, enabling the elastomer to completely
fill the bead area.

However, when there is no fabric in the bead (as in a homogeneous

part, or one that the bead is designed onto the elastomer side of the
diaphragm) there is no way of insuring that all the air will be forced out
of the bead. This is due to the fact that the bead’s geometry prevents
The first consideration is how much to deflect the rubber to effect
the elastomer from moving in a straight path (Fig. 2) keeping the air in
a seal. This number may change for some compounds but generally
we recommend a minimum of 20% deflection of the elastomer front of it. To solve this problem we recommend moving the parting
(B dim Fig.1). This number insures that the seal will be maintained line to the opposite side of the bead (Fig. 3). This enables the elastomer
even after the elastomer takes its compression set. Since the flange to move in a straight path keeping all the air in front it and insuring
thickness and the hardware dimensions need tolerances, the design
that the volume and height of your bead remain constant. There are no
should be calculated at 25% +/- 5%. This generally is enough to
allow for normal tolerancing of the hardware to insure a good seal. special bead groove requirements for this because there is no increase
However, there are those situations where the variation in elastomer in volume of elastomer. It is important to remember that you are
thickness, or hardware dimensioning is such that it is impossible to obtaining the seal by deflecting the bead from top to bottom, not side
keep everything in the range to maintain the 20% to 30% deflection.
to side.
In cases such as these we recommend that the deflection exceeds the
30% rather than go below the 20%. Figure 2

The key point that must be remembered when designing a bead

and bead groove, is that the elastomer is incompressible. When you
deflect it 25% to form a seal the elastomer needs a place to go. If
you haven’t provided that room in the groove area of your hardware,
then the elastomer will flow out of the groove into the working area
of the diaphragm. This can cause cracking in the flange radius area
of the diaphragm, or enough distortion in the diaphragm to cause
the two sidewalls to come together, resulting in failure. To avoid
these problems, simply design your bead groove so that when the
hardware is assembled the volume of the groove is such that it can
contain the largest bead the spec will allow (A, Fig.1).

12 © 2018 DiaCom Corporation

 Beadse

Beads can be added to the diaphragm in an almost infinite variety of shapes and sizes. However, there are many things to consider before
adding beads to the diaphragm design. Not the least of which, is the impact on the cost of the diaphragm. Most beads are added to a
diaphragm to be used as the sealing mechanism in the final application.

Beads are formed during the molding operation by flowing rubber into the mold cavity, filling the bead area while driving out the air. There
are several limitations on bead design that must be considered due to this rubber flow. Bead location, shape, size, mold parting line, and etc.
must all be carefully considered. The examples below illustrate some of the changes that can improve the quality of the diaphragms. These
design changes are often driven by the location of the fabric reinforcement (the location of the fabric is shown below by the F symbol), but
these design recommendations also apply to homogeneous (all-rubber) as well as double-coated diaphragms.

As Designed Recommended

© 2018 DiaCom Corporation 13

 Type F Diaphragms

General Description
The Type F diaphragm is commonly referred to as the “top The flange of the Type F diaphragm is designed to seal like a
hat” diaphragm (Figure 2). It exhibits all of the benefits that gasket between the two flat surfaces of the cylinder and bonnet.
are associated with rolling diaphragms. These diaphragms The outside edge and bolt holes can be cut into any configuration
have the longest stroke-to-bore ratio, zero spring rate, no desired. An effective seal should be obtained by compressing the
break away friction, constant effective pressure area, and flange area 20 – 30% by thickness.
long life. Some of the drawbacks to Type F diaphragms are:
additional assembly time required when inverting the top To extend cycle life and reduce “four cornering” of the diaphragm,
head corner radius during installation, and an inability to a double taper design may be utilized (see Figure 1). This design
withstand reverse pressure. reduces the diameter of the bottom end of the diaphragm which
minimizes excess material in this area and relieves circumferential
Dimensions and Tolerances compressive stress.

Double Taper Diaphragm - Figure 1 Top Hat Diaphragm - Figure 2

Head

Millimeters in Red

Hole Spacing for Type F and FC Diaphragms

Hole Spacing:
Perforations through the head or the flange should be located so that there is at least
.100 inches minimum between the edges of holes. Also, holes should be located so
that there is at least .125 inches between the edge of a hole and the trim periphery.
It is also important to arrange the hole pattern so that the radial distance from the
edge of the hole to the start of the blend radius at either the piston head or cylinder
clamp flange is at least as far as indicated in the chart above.
14 Millimeters in Red © 2018 DiaCom Corporation
 Available Sizes Type F Diaphragmsl

© 2018 DiaCom Corporation Millimeters in Red/*Metric Effective Pressure Area shown in Square Centimeters 15
 Type FC Diaphragms

General Description
In this style, the piston and the flange are molded on the to-bore ratio. To improve this ratio, an offset preconvoluted
same plane. The benefit of this style is that the handwork of diaphragm can be designed (see FC Offset figure at bottom
forming the convolution is eliminated, which greatly reduces of page). In this shape, the piston head and flange are molded
the assembly time. This would be of importance in high volume offset to each other, thereby putting all the additional stroke
applications. The drawbacks to this type of diaphragm are: a capabilities on one side of the convolution. This provides a
built-in spring rate, due to the molded-in convolution, which longer stroking diaphragm which still maintains the assembly
must be considered during the design stage, and a limited stroke- ease of a preconvoluted diaphragm.

Dimensions and Tolerances

0.38

0.38
Head

Note: Please See Page 14 Type F Diaphragms) for Hole Spacing Information.

FC Offset

16 Millimeters in Red © 2018 DiaCom Corporation

 Available Sizes Type FC DIaphragmsl

© 2018 DiaCom Corporation Millimeters in Red / *Metric Effective Pressure Area shown in Square Centimeters 17
 Type D Diaphragms

General Description
This style diaphragm is the same as the Type F in all respects the bead into a properly-sized groove (see table at bottom of
except flange mounting. The parts are molded with what equates page). The cylinder and bonnet can then be designed to make
to half of an O-ring on the flange rather than a large flat positive contact when assembled, eliminating the need for a
surface. This O-Ring half fits into a groove machined into the closely controlled assembly torque. It also reduces the overall
cylinder half of the hardware. Sealing is achieved by squeezing diameter of the diaphragm, reducing the hardware diameter.

Dimensions and Tolerances

Hardware Recommendations

18 Millimeters in Red © 2018 DiaCom Corporation

 Available Sizes Type D Diaphragmsl

© 2018 DiaCom Corporation Millimeters in Red/*Metric Effective Pressure Area shown in Square Centimeters 19
Type DC Diaphragms

General Description
This style diaphragm is similar in function to the Type FC diaphragm, while the sealing and hardware designs are the same as
the Type D.

Dimensions and Tolerances

Hardware Recommendations

Available Sizes

20 Millimeters in Red/*Metric Effective Pressure Area shown in Square Centimeters © 2018 DiaCom Corporation
 Type O and OA Diaphragmsl

General Description
Type O – This type of diaphragm has no flange. An O-ring is molded Type OA – This diaphragm type is a second generation to the Type O
to the bottom of the sidewall. Unlike the other types of diaphragms, and fits into identical hardware. It differs from the Type O in that its
the Type O is put into convolution by folding the sidewall back onto sidewall attaches to the inside diameter of the O-ring and the fabric
itself. The bead is then squeezed into a groove machined into the is on the outside, requiring the head corner radius to be inverted for
bonnet half of the hardware. This type enables the greatest reduction installation. The Type OA tends to be easier to install, but basically the
in hardware diameter, while keeping a full stroke potential. difference is personal preference.
Dimensions and Tolerances
TYPE O TYPE OA

Hardware Design

Available Sizes

© 2018 DiaCom Corporation Millimeters in Red/*Metric Effective Pressure Area shown in Square Centimeters 21
Type OB Diaphragms

General Description
Type OB diaphragms have a rectangular bead molded inside same height. Because the clamping and sealing of this style diaphragm
their cylinder wall. This design requires the smallest hardware is against the inside wall of the cylinder, the stroke is restricted to the
diameter of any diaphragm type. The Type OB diaphragm has lower half of the diaphragm.
only half the stroke capability of other diaphragm styles of the
Hardware Design Dimensions and Tolerances
Stamped Retainer Plate
Sealing Via
Axial Compression

Cast Machined Retainer Plate

Sealing Via
Radial Compression

Available Sizes

22 Millimeters in Red/*Metric Effective Pressure Area shown in Square Centimeters © 2018 DiaCom Corporation
 Type P Diaphragmsl

General Description
This diaphragm type, commonly referred to as dish-shaped, coated to take pressure in both directions. Due to its wide
has a sidewall that slopes gradually from the cylinder convolution and gradual sidewall slope, the total travel
to the piston. This diaphragm is designed to be flexed and ability to withstand high pressures are limited. The
in both directions to its full height. It may be double- effective pressure also varies through its stroke.
Dimensions and Tolerances

Available Sizes

Elastomer & Fabric Data

Fabric Data Elastomer Data
G e n e r a l l y, f a b r i c r e i n f o r c e m e n t i s r e q u i r e d w h e n The chart on page 25 lists common elastomers, some
p r e s s u r e d i f f e r e n t i a l s e xc e e d 5 p s i a c r o s s t h e d i a p h r a g m . physical properties, and compatibility to common
S o m e a p p l i c a t i o n s m ay r e q u i r e e l a s t o m e r i c c o a t i n g s o n chemicals. Other DiaCom specialty elastomer compounds
b o t h s i d e s o f t h e f a b r i c. T h e s e m a t e r i a l s a r e ava i l a b l e are available. These include FDA, NSF, and UL-approved
f r o m s t o ck . D u e t o t h e m a n y a p p l i c a t i o n va r i a b l e s, compounds used in potable water, food, dr ug, propane
i t i s r e c o m m e n d e d t h a t a D i a C o m r e p r e s e n t a t ive b e and natural gas applications. Additionally, elastomeric
c o n s u l t e d t o e n s u r e p r o p e r s e l e c t i o n . T h e ch a r t o n silicone/fluorosilicone blends are available for automotive
p a g e 2 4 l i s t s s o m e o f D i a C o m ’s c o m m o n f a b r i c s t y l e s, use. This is a general chart and is in no way intended as
a s we l l a s s o m e g e n e r a l p hy s i c a l ch a r a c t e r i s t i c s o f the final guide to material selection. Contact a DiaCom
va r i o u s f a b r i c f i b e r s. representative for proper elastomer selection.

© 2018 DiaCom Corporation Millimeters in Red/*Metric Effective Pressure Area shown in Square Centimeters 23
 Typical Fabric Characteristics
Maximum Recom- Fabric
DiaCom Fabric Gauge
Fabric Type mended Operating Tensile Strength General Physical Properties
Fabric Style (Inches)
Temperature (Pounds/Inch)
FA-0321 Polyester .0031-.0040 150°C (302°F) 34 Light weight, special applications
FA-0503 Polyester .0020 -.0052 150°C (302°F) 66 General purpose, high stability, good processability
FA-0708 Polyester .0078 -.0086 150°C (302°F) 154 Heavy duty, high stability
FA-0801 Polyester .0085 -.0105 150°C (302°F) 35 Light to medium duty, good formability
FA-0806 Polyester .0085 -.0105 150°C (302°F) 35 Light to medium duty, good formability
FA-0919 Polyester .0075 -.0095 150°C (302°F) 80 Tight weave, high-strength
FA-0920 Polyester .0075 -.0095 150°C (302°F) 80 Tight weave, high-strength
FA-1202 Polyester .0088 -.0128 150°C (302°F) 114 Heavy duty, good formability
FA-1601 Polyester .0140 -.0160 150°C (302°F) 70 Medium duty, good formability
FA-2309 Polyester .0220 -.0250 150°C (302­°F) 390 Open weave, heavy duty, good formability
FB-1111 Nylon .0142 - .0154 120­°C (250°F) 275 High strength, good formability
FB-2004 Nylon .0260 - 0.280 120­°C (250°F) 862 High strength, average forming capability
FB-2806 Nylon .0250 - .0280 120­°C (250°F) 825 Extreme heavy duty, good abrasion resistance
FB-3701 Nylon .0355 - .0395 120­°C (250°F) 825 High strength, average forming capability
FC-0604 Nomex .0068 - .0077 260°C (500­°F) 115 High temperature, heavy duty
FC-0702 Nomex .0073 -.0091 260°C (500­°F) 42 High temperature, light to medium duty, good formability
FC-0905 Nomex .0084. - .0096 260°C (500­°F) 105 High temperature, heavy duty, limited formability
FV-1001B Dia·Tuff™ .0090 -.0130 260°C (500­°F) 600 Extreme heavy duty, good formability
FCDA-1015 Viton® Coated Polyester .0090 -.0120 150°C (302°F) 50 Medium duty, good chemical resistance
FCGB-0806 Nitrile Coated Nylon .0075 -.0085 120°C (250­°F) 150 Medium duty, good formability
FCGB-1325 Nitrile Coated Nylon .0110 - .0150 120°C (250­°F) 150 Medium duty, good formability
FCGB-1330 Nitrile Coated Nylon .0110 - .0150 120°C (250­°F) 150 Medium duty, good formability
FCGB-1251 Nitrile Coated Nylon .1130 - .1370 120°C (250­°F) 350 High strength, good formability
FCGB-8513 Nitrile Coated Nylon .0820 - .0900 120°C (250­°F) 350 High strength, limited form-bilty
FCGD-0602 Nitrile Coated Silk .0050 - .0065 100°C (212­°F) 28 Ultra sensitive, fuel resistant
FCGE-1032 Nitrile Coated Cotton .0080 - .0120 150°C (302­°F) 55 Medium Duty, good formbility
FCGA-0605 Nitrile Coated Polyester .0050 -.0070 120°C (250­°F) 100 Medium Duty, good formability

GENERAL CHEMICAL COMPATIBILITY

PROPERTY: SILK COTTON NYLON POLYESTER NOMEX Dia·Tuff™

RELATIVE TENSILE STRENGTH Moderate Moderate Very High High High Extreme

RESISTANCE TO:
HEAT DEGRADATION LOW GOOD VERY GOOD VERY GOOD EXCELLENT EXCELLENT
MILDEW FAIR POOR-FAIR GOOD GOOD EXCELLENT EXCELLENT
ALKALIS POOR GOOD GOOD FAIR GOOD GOOD
WEAK ACIDS FAIR GOOD FAIR GOOD FAIR GOOD
STRONG ACIDS POOR POOR POOR FAIR-GOOD POOR EXCELLENT
OXIDIZING AGENTS POOR FAIR FAIR GOOD POOR EXCELLENT
ORGANIC SOLVENTS POOR EXCELLENT VERY GOOD GOOD GOOD EXCELLENT
RELATIVE COST MOD-HIGH MODERATE MODERATE MODERATE HIGH VERY HIGH
The data shown in these charts and tables is based upon information from material suppliers and careful examination of available publications and is believed to be accurate and reliable; however, it is the user’s responsibility to determine suitability for use. You should thoroughly test any proposed
use of our materials and independently conclude satisfactory performance in your application. For more information call the DiaCom Corporation, 5 Howe Drive, Amherst, NH 03031 - Tel. 603-880-1900

24 © 2018 DiaCom Corporation

 25
Chemical Compatibility Table

© 2018 DiaCom Corporation

 Diaphragm Seals
Application Data Form
Thank you for your request for engineering assistance. Answers to the following questions will provide our Engineering department with
information to assist in the analysis of your specific application. Please make sure to provide as much information as available. Where
possible, please provide prints, layouts, or sketches of the proposed diaphragm and installation.

Type of mounting inches Cylinder Bore Diameter inches

Piston Diameter inches Height inches
Up-Stroke inches Minimum Operating Temperature ºF
Down-Stroke* inches Normal Operating Temperature ºF
Total Stroke inches Maximum Temperature ºF
Minimum Pressure psi Time Interval at High Temperature:
Normal Pressure psi
Maximum Pressure** psi * Stroke as measured from Flange
Reverse Pressure psi ** Operating and Surge
Pressure Differential: psi

Fluid or gas in contact with Diaphragm on High Pressure Side: ________________________________________________

Fluid or Gas in contact with Diaphragm on Low Pressure Side: ________________________________________________
Estimated # of Cycles Required for Satisfactory Performance: ________________ Approximate Cycle Rate: ____________
Trim & Perforation Requirements: ______________________________________________________________________
Submit sketch or drawing if special trim/perforation requirements.)
Annual Quantity Requirements: ____________________ Delivery/Release Requirements: ___________________________
Customer Part or Print Number: ___________________

(If this is a current production part, please indicate any quality or performance problems you are encountering. If appropriate, submit a sample part for
Engineering evaluation.)

Please list any special requirements or environmental considerations not listed above: ______________________________________________________
________________________________________________________________________________________________________________________
Please Print Below:
Date:
Name:_____________________________________________ Title: _____________________________
Company: __________________________________________ Phone: ____________________________
Street Address: ______________________________________ Fax: ______________________________
City: ___________________________ State: _______ Country: _________________

Diaphragm Design & Manufacturing Leader

DiaCom Corporation, an ISO 9001 and AS9100 certified company, is a recognized leader in the design, manufacture
and application of innovative, high performance molded diaphragm seals. DiaCom serves a variety of markets world-
wide including industrial, automotive, aerospace, food processing, water controls, medical instrumentation, appliances
and others. DiaCom offers state-of-the-art diaphragms designed for cost effectiveness, ease of installation, durability,
and high performance characteristics.

DIA·COM CORPORATION
The Diaphragm Company
Online Guidebook: www.diacom.com

5 Howe Drive Amherst, NH 03031 USA

Phone: 800.632.5681 603.880.1900 Fax: 603.880.7616
Internet: www.diacom.com Email: sales@diacom.com

The information shown is based upon information from material suppliers and careful examination of available publications and is believed to be accurate and reliable; however, it is the user’s responsibility
to determine suitability for use. You should thoroughly test any proposed use of our materials and independently conclude satisfactory performance in your application.

26 © 2018 DiaCom Corporation

 The DiaCom Advantagel
Quality Management
DiaCom’s Quality Systems are certified to AS-9100 Quality Management System, an International
Standard developed to assure customer satisfaction. AS-9100 uses a process approach when developing,
implementing, and improving the effectiveness of a quality management system. Diacom’s “DiaTrac”
system enables 100% lot traceability. SPC, FMEA’s, 8-D analysis, Process Control Plans, and Process
Capability Studies are routinely used in accordance with manufacturing requirements. Zero-defect
sampling and continual in-process quality audits insure dimensional and material integrity.

State-of-the-Art Production Facilities

Microprocessor-controlled production presses designed specifically for the
production of fabric-reinforced and homogeneous elastomeric diaphragms.
Our new production presses are built with high-strength components. The
microprocessors closely control the vulcanization process, thus assuring
precise, repeatable control of the molding process. The result is high quality,
low cost diaphragm production. DiaCom utilizes unique compression and
transfer molding processes to maximize efficiencies and insure the dimensional
integrity of each part.

In-House Design
Computer Aided Drafting electronically enhances DiaCom’s abilities to
provide accurate customer tooling designs on a timely basis. DiaCom’s
application engineers routinely assist customers in the design of 3-D
drawings, standard, or special diaphragm. We are able to accept most
popular formats of CAD drawings, including: Solid Edge, STEP, IGES,
DXF and others. DiaCom uses only high strength steel for production
and prototype molds. DiaCom’s internal tool shop has complete CNC
machining capabilities that allows for quick turnaround on prototype and
production tooling.

Engineering Experience
DiaCom Engineers routinely work with our customer engineering personnel to
transform application concepts first into fully functioning prototypes, and ultimately,
into production units. Our experience and background allow us to cost-effectively
provide a diaphragm that meets or exceeds all customer’s diaphragm expectations.
Using Auto-Cad drafting software, we are able to communicate electronically with our
customers to accelerate the design process. Existing diaphragm applications sometimes
do not perform as well as intended. Our technical staff is available as an aid to our
customers to analyze performance issues, offer hardware recommendations, and to
assist in root cause analysis and the implementation of permanent corrective actions.

In-House Rubber Materials Laboratory

Constantly striving to improve existing applications, meeting the demands of new programs,
and trouble shooting application issues, DiaCom has established a Rubber Materials Lab that
gives us significant rubber testing capabilities. Using ASTM standard procedures, we are able
to obtain physical properties, such as, tensile strength, elongation, modulus, durometer, tear
strength, compression set, and rheology data, such as viscosity, cure times, scorch date and
etc. We are also capable of running a variety of chemical compatibility testing, heat aging,
volume swells, etc. using ASTM standard testing procedures, and we can run customer-specific
tests. DiaCom can custom formulate materials to meet virtually any application environment.
Combining this test capability with our technical expertise allows us to provide materials that
meet customer specifications, ASTM material call-out and other certification bodies, such as
UL or NSF.

© 2018 DiaCom Corporation 27

 Molded Diaphragms: Ideal solutions to tough sealing problems.

The Diaphragm Company

Corporate Headquarters:
5 Howe Drive Amherst, NH 03031 USA

Phone (US Only): 800.632.5681 603.880.1900 Fax: 603.880.7616

Internet: www.diacom.com Email: sales@diacom.com

The information contained herein is believed to be reliable, but no representations, guarantees or warranties of any kind are made as to its accuracy, suitability for
particular applications or the results to be obtained therefrom. Nothing contained herein is to be considered as permission, recommendation, nor as an inducement to
practice any patented invention without permission of the patent owner.