Bladder accumulators
A bladder accumulator is a hydraulic component consisting of a housing (very often steel but also carbon fiber reinforced plastic ) and an accumulator bladder . The device is used for energy storage or as an expansion tank for pulsation damping .
Bladder accumulators as expansion vessels in heating systems are called diaphragm expansion vessels (MAG) and as part of the hydropneumatic suspension in vehicles from the manufacturer Citroen Federkugel .
A hydraulic fluid is pressed into this reservoir against a gas (usually nitrogen ). Gas and hydraulic fluid are separated by an elastomer bladder. The most frequently used bladders are made of nitrile rubber with the abbreviation NBR or HNBR . Other materials are FKM , epichlorohydrin rubber (ECO), IIR , EPDM and special mixtures for special fluids or temperatures.
Bladder accumulators are usually filled on the gas side with nitrogen or with compressed air , rarely with other gases. The bladder is thus compressible. This compressibility makes it possible to store energy in the gas space. If the bladder accumulator is filled from the fluid side with the almost incompressible hydraulic fluid , the bladder is deformed. The compression ratio, maximum bubble volume to minimum bubble volume, should not exceed 4: 1, since in this case the bubble will be deformed too much and can break. Recent developments allow the bladder integrity to be monitored to detect the bladder rupture. A sensor is built into the bladder and the signal is evaluated by electronics.
When calculating the size of the bladder accumulator, the thermodynamic properties of the gases used must be taken into account. The memory manufacturers offer help with their software.
Bladder accumulators are pressure vessels and are subject to the relevant technical regulations and country-specific laws. In Europe, for example, this is Directive 97/23 / EC and Directive 2014/68 / EU (for a detailed interpretation see also EN14359), in the USA and many other countries e.g. B. ASME VIII.
Separation from the diaphragm accumulator
Membrane accumulators are constructed in a similar way to bladder accumulators, but with them the flexible separating medium is not attached centrally to the upper end of the accumulator, but about halfway up the container. As a result, the gas cushion is not enclosed by the hydraulic fluid, as is the case with the bladder accumulator, but the two fluids are separated by the membrane at an "end face".