General description
The shells of bladder and piston type accumulators are manufactured
from homogeneous, seamless tubing. In bladder
accumulators one or both ends is formed hemispherically by
either spinning or hammering operations. Strict heat treatment
and stress relieving is performed on all shells after the forging
operation to ensure compliance with the required mechanical
properties.
A full range of bladders have been developed from the most
advanced elastomers capable of meeting low temperatures
(down to -50°F) and high temperatures (up to 300°F). These
same bladder materials are compatible with most fluids.
The fluid port incorporates a poppet valve which prevents the
extrusion of the bladder. Special care has been taken in the
design of the fluid port assembly to prevent turbulent flow,
pressure drop, and potential preclosure of the poppet valve.
A heavy duty spring prevents premature closure of the poppet
valve.
The design of the bladder accumulator makes use of the
considerable difference in compressibility between a gas and
fluid. The bladder contained in the shell is precharged with
nitrogen gas to a pressure determined by the work to be done.
After precharging, the bladder occupies the whole volume of
the shell and from there the process can be split into three
stages.
Stage 1: When the hydraulic pump in the system causes the
fluid to enter the accumulator, the nitrogen contained in the
bladder compresses and its pressure is increased.
Stage 2: The deformation of the bladder ceases when the
pressure of the fluid and the nitrogen become balanced.
During this stage the bladder is not subject to any abnormal
mechanical stress and due to its design deforms sideways
forming three lobes.
Stage 3: On demand, system pressure falls and the stored
fluid is returned to the system under pressure exerted by the
compressed nitrogen. On completion of the hydraulic system
functions, the accumulator returns to stage 1.
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