Page 430 - Mechatronics with Experiments

JWST499-Cetinkunt
JWST499-c07
416 MECHATRONICS Printer: Yet to Come October 9, 2014 8:41 254mm×178mm
Charging Charging
valve Charging valve
valve
Gas cap
Shell
Shell Gas
Gas
Gas
Bladder Body

Poppet Piston
Diaphram Button
Spring
Hydraulic
Fluid port
Hydraulic cap
port
Bladder Diaphragm Piston
(a)

Empty Precharged Line pressure Line pressure Line pressure Min accumulator
higher than P acc is at max value lower than pressure reached
accumulator
(b) pressure
FIGURE 7.8: (a) Three different types of hydro-pneumatic accumulators: bladder type,
diaphragm type, and piston type [13], and (b) various operating conditions of an accumulator
(from left to right): 1) empty (uncharged), 2) precharged, 3) line pressure exceeds the precharge
pressure and fluid flows into the accumulator, 4) line pressure is at maximum and accumulator
is filled with fluid to its design capacity and the line relief-valve should open, 5) line pressure
drops below the current accumulator gas pressure and fluid flows out of the accumulator, 6)
line pressure is at its minimum and the accumulator has discharged all of its designed
discharge volume. Reproduced with permission from Parker Hannefin.

until the pressure rises to the maximum pressure setting, at which point the relief valve
opens. When the stored pressure in the accumulator is larger than the line pressure, that
is due to sudden pressure drop in the line, the fluid flows from the accumulator to the
line. This continues until the accumulator pressure reaches the minimum pressure setting,
at which point the poppet valve would be closed. When the line pressure exceeds the
accumulator pressure, fluid again flows into the accumulator and charges it. The pressure
in the accumulator is limited to be between minimum and maximum pressure settings,

p min ≤ p acc ≤ p max (7.3)

Whenever p acc ≤ p line , the accumulator is charged, and whenever p acc ≥ p line , the accumu-
lator is discharged. When p acc = p min ≥ p line , the poppet valve closes (or in case of a piston