Diaphragm Classes

Diaphragm Classes Class 3

Class 3

Class 3 Bellofram Rolling Diaphragms employ a beaded flange. The flange is similar to an “O”-Ring and seals the diaphragm via axial compression of the “D” shaped bead.

The bead is installed in a housing having mating groove. This design eliminates the need for any perforations in the diaphragm flange, since it is retained by squeezing the bead into its mating groove.

Because the “D” shaped bead loses some of its effectiveness at high pressures as a result of sidewall stress, this design is not recommended where differential pressures exceed 150 psi.

The convolution is formed by inverting the top head corner radius around its entire periphery during installation. To insure that the piston corner radius does not return to its “as-molded” shape, a curved lip retainer plate is generally recommended.

Class 3
DC .25 to .99 1.00 to 2.50 2.51 to 4.00 4.01 to 8.00 8.01 and up
H As required to yield design stroke (See standard size tables and Note 3 below.)
DC Tolerances on DC and DP are ± .010” per inch of diameter but the tolerance will be no less than ±.010" or greater than ±.060"
WH & WF .020 ± .005 .020 ± .005 .030 ± .005 .035 ± .005 .045 ± .007
Wsw .015 ± .003 (Code “B”) .017 ± .003 (Code “C”) .024 ± .004 (Code “D”) .035 ± .005 (Code “F”) .045 ± .007 (Code “H”)
.017 ± .003 1/16 R. 3/32 R. 1/8 R. 1/8 R.
A .025 Max. .025 Max. .035 Max. .040 Max. .056 Max.
B .025 Max. .025 Max. .035 Max. .040 Max. .056 Max.
E 3/32 R. 1/8 R. 5/32 R. 1/4 R. 1/4 R.
F 1/32 R. 1/16 R. 3/32 R. 1/8 R. 1/8 R.


  1. Standards are supplied with a button on the pressure side. 1/8” diameter x 3/32” high on bore sizes 1” and over.
  2. The radius is not the piston radius since the head corner will be inverted at assembly.
  3. Height should not exceed the bore (DC). Tolerance on height to be no less than ±.015” per inch of height.
  4. This “V” rib is for diaphragm processing only. It may not appear on all diaphragms. It is not functional and need not be completely filled. Rib is normally on rubber side of diaphragm.
  5. Two “V” ribs may be used on beads that are .25 or larger in width.
  6. Number, size, spacing and location of “V” ribs may be modified to suit specific beads, or may be left off altogether.
  7. Trim tolerances:
    Hole Diameter OD Trim
    Diameter Tolerances
    0-1.00” ±.010”
    1.01 - 3.00” ±.015”
    over 3.00” ±.020”
  8. Dimensions and tolerances pertain to Bellofram
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