Non-Return Valve - Grundfos Multilift MD Serie Instrucciones De Instalación Y Funcionamiento

5.1.5 Non-return valve

The DN 80 non-return valve includes a drain screw to lift up the
internal flap in order to drain the discharge pipe in case of
maintenance or service. The valve is designed and tested
according to EN12050-4. See fig. 5.
Loosen the lock nut a little before turning the drain
Note
screw.
Fig. 5 Butterfly (double) non-return valve, DN 80
5.1.6 Level sensor
The piezoresistive pressure sensor placed in the controller is
connected via a hose to a pressure tube in the tank. The screw
cap where the hose is connected includes a connection for a DN
100 tube. This tube, the pressure tube, extends down into the
tank. The rising liquid level compresses the air inside the
pressure tube and hose, and the piezoresistive sensor transforms
the changing pressure into an analogue signal. The control box
uses the analogue signal to start and stop the pump and to
indicate high water-level alarm. The pressure tube is fixed
underneath the screw cap and can be taken out for maintenance,
service and for cleaning the inside of the tube. An O-ring ensures
tightness.
The hose is supplied in lengths of 4 or 10 m. The hose must be
connected to the controller.
Fig. 6 Screw cap with hose, DN 100 tube
5.2 LC 221 controller
The LC 221 is a level controller specially designed for controlling
and monitoring the Grundfos lifting stations, Multilift MD and
MLD. The basis for the control is the signal received continuously
from the piezoresistive, analogue level sensor.
The level controller switches the MD and MLD Multilift pumps on
and off according to the liquid level measured by the level sensor.
When the first start level is reached, the first pump will start, and
when the liquid level has been lowered to the stop level, the pump
will be stopped by the controller. If the liquid level rises up to the
second start level, the second pump will also start, and when the
liquid level has been lowered to the stop level, the pumps will be
stopped by the controller.
Starts alternate between the two pumps.
In case of pump failure in one pump, the other pump will take
over (automatic pump changeover).
An alarm will be indicated in case of high water-level in the tank,
pump failure, etc.
Furthermore, the level controller has many more functions as
described below.
Fig. 7 LC 221 level controller for Multilift MD and MLD
The LC 221 controller has the following functions:
• on/off control of two wastewater pumps based on a continuous
signal from a piezoresistive level sensor with alternating
operation and automatic changeover in case of pump failure
• motor protection with motor-protective circuit breaker and/or
current measurement as well as connection of thermal
switches
• motor protection via operating-time limitation with subsequent
emergency operation. Normal operating times are max.
25 seconds (MD) and 55 seconds (MLD), and the operating
time is limited to three minutes (see section
fault indications, fault code F011).
• automatic test runs (2 seconds) during long periods of
inactivity (24 hours after last operation)
• re-starting delay up to 45 seconds after returning from power
cut-off to mains operation (in order to even out the mains load
when several appliances are started up at the same time)
6.4 Description of
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