Hydraulikpresse - Hansa Flex

hydraulic technics & security Hydraulik-TecHnik & sicHerHeiT
pressure peaks –
cause and effecT
pressure peaks are destructive to hydraulic components. and the destructive
effect is created not so much by the magnitude of the pressure
spike as by the temporal rate at which the pressure rise occurs. This is
called the rate of pressure rise (dp/dt) and is measured in bar/s. The faster
the pressure rises, the greater the rate of pressure rise. for example, if the
pressure in a hydraulic system increases from 0 to 250 bar in 0.002 seconds,
the rate of pressure rise (250/0.002) is recorded as 125,000 bar/s. a value
that is not uncommon in hydraulic systems, but can have a catastrophic effect
on moving parts.
correcT MeasurinG equipMenT
in order to measure pressure peaks, the measuring instruments must be capable
of recording data in the millisecond range. this is only possible with electronic
devices with a scanning rate of at least 1,000 hz (1,000 values per second). at the
same time, the magnitude of the pressure peak alone does not yield sufficient
information. the time over which the pressure rose must also be determined.
causes
if pressure peaks occur regularly, threaded connections and seals are being overloaded
constantly. leaks will inevitably occur, and this will force shutdown of
the machinery. and the occurrence of pressure peaks can be attributed to many
factors. if there is air in the hydraulic system, the accelerated oil column collides
with the air bubble at high speed and compresses it. this causes the oil column to
decelerate sharply. in this case, the cause is the kinetic energy of the oil column.
pressure peaks can also arise during fast switching operations. under these conditions,
the oil column is accelerated rapidly and then slowed down quickly. this has
a damaging effect particularly in long pipelines. rapid switching operations at
directional control valves often create pressure peaks, especially in the presence
of a large pressure differential. extreme values are produced in the presence of
negative pressure with dissolved air. return lines are particularly susceptible to
this. if 250 bar are suddenly unleashed into the return line, it can have the same
effect as an explosion.
PreSSure PeaKS
caN have the effect
of aN eXPloSioN
opTiMisaTion
all operations for optimising a system should be verified and checked with measurements.
in the first instance, the cause must be found, then the optimisation
must be tested. it is important to ensure that no loss of productivity is caused due
to excessively long switching operations.
offer
the international hydraulics academy (iha) in dresden assists the operators of hydraulic
systems in identifying and eliminating the real cause with modern measuring
equipment and comprehensive expertise.
source: dipl.-ing. dierk peitsmeyer (international Hydraulics academy, dresden)
HYDRAULIKPRESSE 1|2011
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