They represent characteristic operating pressure-time curves for cylinders and make it easier to categorise cylinders with widely varying requirement profiles in relation to their load. Five basic load types are defined:
Quasi-static pressure:
Characteristic: max. operating pressure is less than or equal to the nominal pressure p N . Superimposed pressure fluctuations do not exceed p N and are smaller than 0.3 p N (Figure B 6).
Pressure pulsation around an average:
During a load cycle the operating pressure fluctuates approximately periodically around pN as the average pressure. The swing p S of the pulsation is <0.5 p N .
Calculation: static against deformation and overload fracture with p A = 1.25 p N ; dynamic against endurance fracture with an oscillation amplitude = p S /2 around the average p N (Figure B 7).
Swelling pressure with added pressure fluctuations:
Approximately constant pulsation width; superimposed pressure oscillations can rise to 30 bar above p N.
Calculation: static against deformation and overload fracture as well as dynamic against fatigue fracture, each with pN + 30 bar (Figure B 8).
Swelling pressure in the limited life range:
Approximately constant pulsation width; the operating pressure-time curve does not exceed p N .
Calculation: static against deformation and overload fracture as well as dynamic against fatigue fracture, each with p N (Figure B 9).
Swelling pressure with added pressure fluctuations and peaks:
Basic load is a pulsating load with superimposed pressure fluctuations up to 25 % above p N : pulsation width p S ≤0.5 p N. Additionally pressure peaks occur.
Calculation: check either fatigue or endurance behaviour; verification of strength by means of test under operating conditions, as the effect of the pressure peaks cannot be calculated (Figure B 10).
Figure B 6: Load model with quasi-static pressure
Figure B 7: Load model with pressure pulsation
Figure B 8: Load model with swelling pressure and pressure fluctuations
Figure B 9: Load model with swelling pressure in limited life range
Figure B 10: Load model with swelling pressure with added pressure fluctuations