Hydraulic installations
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© Lutz-Jesco GmbH 2020
Subject to technical changes.
200318
BA-10491-02-V01
Piston diaphragm dosing pump
MEMDOS KMS LB/LA
Operating instructions
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The pressure on the suction side is higher than on the discharge side
or if you intend to carry out dosing into depressurized lines
In cases like this, if you do not use a back-pressure valve, imprecise dos-
ing results will occur or overloading will result. The back-pressure valve
solves these problems by generating a defined, constant backpressure.
In some circumstances, a back-pressure valve is unnecessary if you use
a hose injection nozzle and if the backpressure that it generates is ade-
quate.
8.5.4 Pulsation dampener
Pulsation dampeners have the following functions:
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Damping pulsating delivery flows for processes that require low-pul-
sation dosing
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Reducing the throughflow resistance with long pipelines
When installed on the suction side:
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Damping of acceleration mass forces and with this reduction of wear
on the dosing pump
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Preventing cavitation (pull-off of the liquid column) due to too high ac-
celeration
However, pulsation dampeners also have important safety functions,
since they prevent pressure peaks from arising that lead to piping vibrat-
ing and cause them to snap.
This problem might occur in the following cases:
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With the high amplitudes of the vibrations
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When using long pipes (the severity of the pulsation increases with
the length of the pipe)
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When using rigid piping instead of elastic hoses
Notes on assembly:
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You should carry out assembly in the direct vicinity of the location
where you want to damp the pressure peaks (directly in front of the
suction valve or directly behind the pressure valve).
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Pulsation dampeners should be installed with throttle valves or
back-pressure valves installed directly behind them. By setting the
valves appropriately, you can further-optimise damping of the pulsa-
tions.
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To prevent unnecessary pipe friction losses, you should lay the con-
necting line straight and in accordance with the rated width of the pul-
sation dampener.
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You must separately fasten relatively large pulsation dampeners and
ones with hose connections.
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Pipelines must not transfer any mechanical tensions onto the pulsa-
tion dampener.
8.5.5 Priming aid
Priming aids are particularly advisable:
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in the case of dosing pumps with small volumetric displacements per
stroke or with low stroke length settings
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With high suction hights
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With highly dense dosing media
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At priming for the first time due to dry valves and air in the suction line
and the dosing head
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In dosing systems with frequent downtimes
Further advantages through priming aids:
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Preventing cavitation in the suction line
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Gas removal
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Optical dosing control with small amounts
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Smoothing of the suction flow
8.5.6 Dosing of suspensions
When dosing suspensions, the dosing head must be rinsed regularly to
prevent depositing. To do this, you install a feed line for the rinsing medi-
um (water) in the suction side installation.
8.5.7 Suction pressure regulator
A suction pressure regulator may be necessary if the suction-side instal-
lation of the system demonstrates a varying suction pressure or supply
pressure:
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Dosing pumps that are installed above dosing tanks deliver less as the
tank empties, since the suction head increases.
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Dosing pumps that are installed below dosing tanks deliver less as the
tank empties, since the positive delivery pressure reduces.
Further problems that can occur:
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Greater wear on the dosing pump, e.g. diaphragm rupture due to the
effects of heavy forces with particularly high tanks and high-density
dosing media.
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Idling of the dosing tank in the case of a diaphragm rupture or pipe
breakage.
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Impermissibly high forces in the pump transmission that occur when
dosing pumps receive the dosing medium directly from the pressure
line.
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Reduced performance or destruction of fittings due to cavitation with
long suction lines.
Installing a suction pressure regulator is a remedy for the problems
above. The suction pressure regulator is opened by the dosing pump's
suction pressure. This ensures that no dosing medium can flow if the
dosing pump is not running or no vacuum can be generated following a
pipe fracture.
Notes on assembly:
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When using a large suction pressure regulator, you should provide a
pulsation dampener on the suction side.
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Installation examples are not shown in the explanations of the acces-
sories.
