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.
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.
FABRIC-COATED RUBBER DIAPHRAGMS
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.
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-Coated Fabric
Have a look to the rubber-coated fabrics that Cervellati sells, clicking here!
REINFORCED DIAPHRAGMS
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.
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.
Disadvantages:
– 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.
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 |