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900 Automatic Advance LN2 microdosing pump

Specifications and Options

Norhof LN2 microdosing systems

Liquid Nitrogen (LN2) is used as the cooling medium and is taken from a storage vessel (Dewar) with low pressure (max. 300 mBar) and delivered (pumped) through a fill line to the application in a micro dosing way.

The Norhof LN2 microdosing system is designed to overcome the drawbacks of LN2 under pressure in which a solenoid valve is used to switch the supply ON / OFF. You may compare the Norhof system with a water tap, but instead of giving water, it gently gives liquid nitrogen, with an adjustable flow, possible to regulate from some drops, up to 1 Liter/minute. Our pump can pump LN2 up to 5 meters above the pump itself.

Working principle

The pressure above the liquid level inside the Dewar is built by heating a small amount of liquid in the bottom of the Dewar. With only up to 100 mBar of over-pressure, the liquid will gentle rise out of the rise pipe and fall into the fill hose. Because we evaporate some LN2 to build pressure, there is no adding of ice inside the Dewar, such as with manual systems which use air from the environment.

When LN2 is required, a small overpressure is generated by a small heater element in the LN2, and liquid flows out of the system like water from a tap, without spilling, noise, vibrations etc.


To display sensor temperatures, vessel pressure, status of LED’s on the pump etc. our Norhof Monitoring software is included with any #900 series pump. This software works under Windows ’98 – 2000 – ME – NT – Vista – W7 – Windows 10 – Windows 11

With each #915 system a software Datalogger function is included. This recorder allows you to document any parameter value over time

With each #915 system 2 application drivers are included. When you are familiar with Visual Basic 6.0 you simply look how our programs are written and use these as a guide for writing your own application driver.

900 series applications

Over the years we encountered various applications for LN2 cooling and came to realize that cooling applications can generally be divided in level control and temperature controlled applications:

Level controlled applications (#905 pump):

– filling cold traps in vacuum systems;
– filling biological storage vessels;
– filling various small vessels one after the other at the press of a button;
– filling actions at timer set intervals;
– maintaining a certain level around 1 sensor;
– maintaining a level between 2 sensors.

In this kind of applications a system is used to transfer liquid from the storage vessel to the application at a given rate, until a sensor or other signal (e.g. switch or timer) stops the flow. This implies “on-off” control of the liquid flow, this with a flow which can be extremely gentle if necessary.

Temperature controlled applications (#910 and #915 pump):

– thermal analysis systems;
– computer controlled freezing;
– gas chromatography;
– temperature stages in microscopes;
– sub-zero temperature control systems;
– stopping chemical reactions;
– cooling of targets, IR cells, cuvettes etc.

In these applications a system is used in a micro-dosing way to bring just enough “cold” to the application as is needed, more at first to achieve the required sub-zero temperature and later less to maintain the temperature. This implies flow control in an analogue fashion of “more-less” based on temperature measurement.

Each system is designed to be truly universal. It’s various built-in modes of operation is of paramount importance for OEM and research applications as one system covers almost all possible needs for cooling, without the need for additional valves, control instruments etc. This means that standardisation within the facility is no longer wishful thinking, despite the various applications.

For any system a host of control possibilities are foreseen. This makes it possible to control a system from existing analytical equipment, PLC’s, simple switches, computers etc. almost without any adaptations.

900 series working modes explanation

On the PCB in the pump, under the cap, is a 16-position switch to select the working mode. This working mode determines how the pump reacts on the sensor, button, RS232 signals, etc.

Each working mode is designed for a specific function.

You must select a working mode (only once) to let the working correspond with your application.

Summary of #900 series

Model:   #905   #910   #915
autonomous operation      √      √      √
remote control by TTL signal      √      √      √
remote control by +24V signal      √      √      √
display system status on PC screen, make hystory file      √      √      √
control flow with 0-5 Volt external signal      –      √      √
control temperature setpoint with 0-5V external signal      –      √      √
control by desktop PC, RS232      –      –      √
Liquid Argon filling option      –      –      √
control by direct RS232 commands      –      –      √

900 series Technical Specifications

Static evaporation rate < 0,5 liters per day
Flow rate adjustable from 0.01mBar to 270 mBar (by potmeter on pump)

== from dripping up to 0.5 Liter/minute

(with a fill line of 2 meter and 4 mm ID)

Maximum working pressure < 300 mBar
Reaction time +/- 2 minutes for cooling down the fill line (with 2 meters fill line)
Power connection 115V / 230V AC with supplied power supply or 12-24 Volt AC/DC
Power consumption average 5 Watts, during pumping 50 watts
Storage container volume 35 Liter 50 Liter 100 Liter
Outside dimensions (diameter) 480 500  mm 500 mm
Height dimensions  791 875  mm 1235 mm
Weight (empty, full) 13 /  41,5 kg 17 / 57,5  kg 32 / 113 kg
Standard fill line 6.25 mm OD, 4 mm ID PTFE tube, with 32mm foam insulation
System includes Dewar, pump, fill line 2.00 m, phase separator, power supply, cables, 2 level sensors, PC software.
Working modes #905, working mode 1 to 7 for level control

#910, working mode 1 to D including temperature control

#915, working mode 1 to F including full RS232 control and Liquid Argon filling possibility

External control #905, 5 volt signals for ON, OFF and RS232 signals for ON, OFF

#910 and #915, more signals to control, depending on mode

PC software Monitor software, to monitor pump behavior, and for some working modes to adjust some parameters.


For #915 advance pump utilities and software for RS232 control

Alarms/warning /  acoustical/ visual /mechanical Dewar empty, Dewar 5 liters LN2 left, broken sensor(s), frozen alarm, mechanical overpressure protection valve.
Options Transport trolley 5 wheels (12 cm height)

Stand for pump (when Dewar is refilled)

Custom built adaptor to fixate sensor(s) on application

All #900 models look the same from the outside and can be internally set in different working modes for the application. All models can be connected to a PC in order to display the status of the system. The software + hardware needed to do this is included with each pump.

Norhof pump stand

Norhof power transformer

Norhof Trolley

50 liter Dewar with trolley

50 liter Dewar with trolley strapped

12 liter Dewar

35 liter Dewar

50 liter Dewar

100 liter Dewar

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