Rubber diaphragms are flexible and airtight components which are employed to divide two chambers with variable volume and pressure.  

Cervellati manufactures three different types of diaphragms:    
–  diaphragms in 100% rubber;
–  diaphragms in rubber-coated fabric;
–  reinforced diaphragms in rubber + fabric insert
which guarantee higher resistance to pressure and to corrosive fluids than all-rubber diaphragms. Their elastic stretching is restrained.rubber diaphragm



Diaphragms advantages:

Compared to pistons or radial seal (Fig. 1), the application of diaphragms offers the following advantages:     
– Perfect airtight seal;   
– Simple assembly;      
– Modest production tolerances and surface finishing;  
– No sliding and static friction; 
– Minimal hysteresis and high degree of sensitivity;      
– No need of lubrication.          




These  diaphragms  are  made   in  a  rubber-coated  fabric and  drawn  by  means  of  a thermoforming  process.  The  rubber-coated  fabric consists  of  a  fabric  insert  coated on both sides by a thin sheet of rubber (Fig. 2).

Compared to the concave membranes, these diaphragms can work at higher pressures.

rubber coated fabric

Technical features:

Available fabric inserts in:  nylon, polyester, cotton, viscose, and polyaramide fibres (for  high temperatures);

Available  rubber coating:  nitrile  rubber,  neoprene,  or  FKM  (for  special applications).

Thickness: normally, between 0.2mm to 1mm.

Addition seal available  in the flanging area  (to make the thin rubber sheet  stronger):   the seal can be obtained with a O-ring type rubber section (Fig. 3) or with gasket in cellulose fibre (Fig. 4)

rubber diaphragm

Rubber-Coated Fabric 


Have a look to the rubber-coated fabrics that Cervellati sells, clicking here!




While  the  diaphragms with  rubber-coated fabric  are made  by shaping  the fabric, the reinforced diaphragms are made by moulding and attaching a fabric insert to the rubber. Cervellati can  produce diaphragms with  rubber and fabric  insert which best suit to the
customers’ needs.  Thickness and shape can vary according to the client’s drawing, so that no additional cardboard gaskets are required.

reinforced diaphragm

The  illustrations  from Fig.10 to Fig.13  show  some  characteristic shapes  of reinforced diaphragms.
The concave diaphragm (Fig. 10) must be assembled to take  on a configuration similar to the convoluted diaphragm (Fig. 11).
The convoluted diaphragm, however, is moulded 
into the same shape that it will take during the assembly phase.


Advantage of the reinforced diaphragms, compared to the diaphragms with rubber-coated fabric:
– Better height-to-diameter ratio, therefore longer travel;
– More efficient seal;
– Greater resistance to pressure;
– Possibility of using all types of rubber and fabric inserts;
– Lower sensitivity and greater hysteresis;
– The ply is not positioned at centre, as with the rubber-coated fabric, but on the outside surface.  As a result, the differential pressure will always be  applied to the side of the rubber.



– Lower sensitivity and greater hysteresis;

– The ply is not positioned at centre, as with the rubber-coated fabric, but on the outside
surface.  As a result,  the differential pressure  will always be applied to the side of the


Diaphragms, in different materials and with different designs, are employed in the following machineries:

– Pressure regulators – Pressure stabilizers
– Flow regulators – Pressure transducers
– Linear actuators – Brakes 
– Pneumatic servo-mechanisms – Pneumatic switches
– Positioning valves – Household hot water regulators
– Safety valves – Dosing pumps
– Acceleration pumps in carburetors      – Waste-gate valves in turbo-compressors