900 Automatic Advance LN2 microdosing pump

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.

Software

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

900 series Technical Specifications

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.