Hydraulic installations
Hydraulic accessories
25
© Lutz-Jesco GmbH 2018
Subject to technical changes.
181112
BA-10407-02-V08
Motor-driven diaphragm dosing pump
MEMDOS LB
Operating instructions
8.5 Hydraulic accessories
The following chapter is intended to give you an overview of installation
options.
Please note that these operating instructions are no substitute for the in-
structions supplied with the accessories in each case. The corresponding
documentation supplied with the product applies to safety information
and provides exact instructions on assembly.
8.5.1 Injection nozzle
If the pressure line enters a main line, it is advisable to install an injection
nozzle.
Injection nozzles have three main functions:
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Dosing the medium into a main line,
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Preventing flowback into the pressure line through a non-return valve.
Notes on assembly:
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Double-ball injection nozzles must be installed into the main line verti-
cally from the bottom. You can install hose and spring-loaded injection
nozzles any way you like.
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With dosing media that tend to crystallize, it is advisable to carry out
installation into the main line from the bottom. This prevents air bub-
bles from being trapped.
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Many dosing media tend to contaminate the injection nozzles, which
can lead to blockages. In cases like this, it is advisable to install an in-
jection nozzle that is easy to dismantle and block off.
8.5.2 Pressure-relief valve
Pressure relief valves have an important safety function for protecting the
dosing pump and the associated pipes and fittings. The dosing pump can
generate a pressure that is many times the rated one. A blocked pressure
line can lead to dosing medium escaping.
An improperly high pressure can occur if:
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the shut-off valves are closed even though the dosing pump is run-
ning,
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pipes block.
At an appropriate pressure, a pressure relief valve opens a bypass line
and protects the system in this way from damage caused by over-pres-
sure.
Notes on assembly:
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The line for returning dosing medium from the pressure relief valve
must be routed to the dosing tank or to a collecting pan.
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The pressure in the dosing tank must not be too high so that it is pos-
sible to accommodate the returned dosing medium.
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As an alternative, the system can return dosing medium into the suc-
tion line in front of the dosing pump. In this case, there must not be a
non-return valve or a foot valve in the suction line.
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You should install the pressure relief valve as close as possible to the
dosing head.
8.5.3 Back-pressure valve
Back-pressure control valves are necessary if:
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there are considerably fluctuating system pressures,
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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 can occur:
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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.
