In many cases it must also maintain a pressure differential between the two media. When installed in the flange of an instrument, it acts as its own gasket to make a fluid-tight seal. Such a diaphragm may be used in control devices, meters, regulators, and pumps. In this case, thick rubber covers are needed to fill in and smooth out the rough impression of the fabric. Large diameters are being sealed.
Flanges are rough or warped within reasonable limits.