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THEORY OF ROLLING DIAPHRAGM OPERATION

Bellofram Rolling Diaphragms are, in effect, pressure vessels having a variable volume and flexible moving side-walls. As in any other pressure vessel, their strength should be considered with respect to safety factors. Generally, they are designed with a large safety factor. This means the maximum safe working pressure will be a fraction of the pressure that could cause failure of the sidewall.The accompanying illustration, Fig. 3, illustrates the pressure reaction of the . Here it can be seen thatalmost the entire pressure load is supported by the piston head. Only a small amount of the liquid or gas pres- sure is supported by the narrow convolution of the rolling diaphragm. Referring to Fig. 4., particularly, to that portion of the convolution in immediate contact with the cylinder and piston walls, it will be noted that the lines of unit pressure (acting in horizontal plane because they must be normal to the surface) force the diaphragm against the piston and cylinder sidewalls.The lines of pressure acting on that portion of the diaphragm not in immediate contact with cylinder and pistonwalls (semi-circular segment of the convolution) are shown in Fig. 4. Each line of unit pressure acts in a direction normal to the semi-circular segment; hence all of the pressure lines can be replaced by their horizontal and ver- tical components. The sum of the vertical components is the total force acting on the semi-circular segment.Actual stress analysis and selection of industrial fabrics will be made by the Bellofram Application Engineering Department. Fig. 3 Fig. 4

DIAPHRAGM APPLICATIONS

The applications for are found in every industry–automotive, agricultural, aerospace, medical, etc. For proper Bellofram Rolling Diaphragm selection the Design Parameter Sheet is an indispensable tool. Thedesign format provides all the necessary data for correct diaphragm design (see page 31). Below is a partial list of applications: Process control Valves Air Industrial pressure regulators Displacement Pumps Liquid Dispensing equipment Valve Positioners Automatic Choke Controls Distributor Vacuum Advance Mechanisms Irrigation Valves Aircraft Environmental Controls Belt Guide Actuators Automotive Locking Hubs Anti-Scald Devices Truck Brake Actuators Automotive Emission Controls Geothermal Pumps Automatic door Locks Tank Truck Valves Water Conditioning Valves Pneumatic relays Dancer Roll ActuatorsIndustrial Brakes Expansion Chambers Automatic Transmission Modulators LP Gas Regulators Timing Chain Tensioners Pressure switches Flow control valves Fire Sprinkler Alarms Domestic Hot Water Regulators Waste Gate Actuators Fuel Pressure controls Vacuum switches Pressure transducers Vacuum regulators Gage Isolators Linear actuators Flush Valves

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