Molded Rubber diaphragm
In contrast to the flat diaphragm, which is stamped from a flat sheet of rubber, the molded Rubber diaphragm is manufactured by pressing the finished part in an axially symmetrical mold. To provide good elastic deformability, the thickness of the diaphragm is reduced towards its circumference. The threaded stud that projects from the lower side of the Rubber diaphragm secures it to the connecting rod. The diaphragm presents an unbroken surface to the compression chamber.
The contour of the pump here can be made to conform very precisely to the form of the diaphragm at full stroke. This means that the dead volume can be reduced to a minimum, so that compared with the flat diaphragm a lower ultimate vacuum is achieved. The unbroken surface of the molded Rubber diaphragm increases the gas-tightness. Only the joint formed by clamping the diaphragm between the crankcase and the pump head, and the permeability of the elastomer from which it is made, set a limit to the possible gas-tightness.
Because the metal parts of the diaphragm are protected by a layer of rubber, the molded diaphragm is particularly important in applications with corrosive or chemically aggressive media. The smooth surface of the diaphragm makes it practicable to coat it, for example, with PTFE, to provide protection against highly aggressive substances. Now, if the components of the pump head are made from PTFE, the resulting pump is reliable, and resistant to chemicals.
The advantages of the molded diaphragm are: Simple and economical design Low wear Makes a low ultimate vacuum possible High gas-tightness Reliable, chemically resistant pump possible Compared to the flat Rubber diaphragm, pump, a molded diaphragm pump of the same size and the same design life has a lower flow rate. Whereas, the central region of the flat diaphragm is rigid the pressure in the compression chamber deforms the molded diaphragm much more; this can result in up to 20% reduction in performance. If the stiff central part of the diaphragm were extended too far without reducing the size of the elastic part, the permissible stresses for the diaphragm material would be exceeded.