A New Technology for Metering Fluids in Medical Devices

Versatile Solutions for Micro-Dispensing

by Dipl.-Ing. Stephan Kaufmann
Graduate engineer Stephan Kaufmann is Head of Development & Design at KNF Flodos AG in Sursee, Switzerland

Chemical analysis, clinical diagnostics, pharmaceutics, process technology, are just a few examples of the many applications where small quantities of liquids need to be dispensed. Diaphragm pumps are amply qualified for such tasks. Boasting four exceptional pump designs, KNF Flodos has the solutions to cater for virtually every requirement.

Introduction

Diaphragm metering pumps offer several major advantages over rival types of pumps. For example, they are self-priming and safe to run dry (i.e. they can also pump air). Diaphragm pumps are ideally suited for volatile media and crystallizing chemical solutions as the diaphragm acts not only as an impeller but as a non-sliding seal. Another advantage is that the media do not become contaminated by abraded particles or lubricants. In terms of engineering, the simple design of the pumps translates to low-maintenance operation and a high level of precision over the entire lifetime of the pump.

The manufacturer has contrived four ingenious technological solutions for diaphragm metering pumps in order to cover the spectrum of problems encountered in simple metering applications right through to complex dispensing tasks. Each of these designs incorporates the specific advantages of diaphragm technology and is suitable for aggressive media.

1- Solenoid-powered diaphragm metering pump / flow-tight in both directions

The FMM20 solenoid-powered diaphragm metering pump was developed for dispensing single doses and runs using the simplest external control with each electric pulse delivering one stroke. A screw allows the dispense volume to be adjusted between 5 and 25 microliters enabling the user to calibrate the pump to fit the system parameters and ambient conditions. Given that the frequency range of the electric pulses can vary from 0 to 20 Hz, the resulting flow rate lies between 0 and 30 milliliters per minute. The FMM20 metering pump boasts an exceptionally long service life and high level of reliability; this is due to a patented valve system and a special surface coating on the moving parts. The pump is also flow-tight in both directions thanks to a newly developed technology which removes the need for a non-return valve in the system or an external solenoid valve. The distinct clicking noise which is characteristic of conventional solenoid-powered diaphragm metering pumps is not encountered with the FMM 20 which runs very quietly, making it suitable for applications where noise is an issue. This can be attributed to a clever patented technology using a stroke limitation and damping system.

2- Micro-diaphragm pumps for simple metering and pumping

Pumps for continuous metering generally offer a number of options in terms of control and operation. Such multiple-feature pumps can be overqualified for some applications which call for the simplicity of the NF 5 KTDCB-4 micro-diaphragm pump.

This proven and tested fluid pump is fitted with a specially developed brushless motor and integrated control electronics, making it suitable for pumping and metering jobs. It enables continuous metering of between 5 and 70 milliliters per minute. With characteristic simplicity the flow rate is controlled by an external direct current input of between 0 and 5 volts which is supplied to the motor via an additional lead. At less than 1 watt the power consumption of the motor is very low. The control electronics combined with the patented diaphragm and valve technology guarantee high pressure stability, consequently the pump speed remains constant even when subject to back-pressure or vacuum. The highly compact design and long service life are outstanding features of this product.

3 - Stepper motor drive for more control and higher pressures

The FEM 1.02 and 1.09 metering pumps also fulfill numerous dosing requirements. Both pumps are driven by a two-phase stepping motor which enables precision speed control, exceptional repeat accuracy and flexibility. Customers who might need to integrate the pump in existing equipment are faced with a straightforward and inexpensive task in that this pump can be run with the most basic stepping motor electronics. However, an electronics module can also be supplied from the factory as an optional extra.

The FEM 1.02 and the FEM 1.09 models can dispense between 0.2 and 20 milliliters per minute and between 0.9 and 90 milliliters per minute respectively. They allow both continuous flow and single doses. Other outstanding features of these metering pumps include their excellent pressure stability, over the entire working range from 0 to 6 bar, and their long-term stability. They can also be supplied with an integrated pressure relief device.

4 -The whole works: metering pump systems

Integrated metering systems comprising pump and control electronics offer multi-faceted versatility in one single product. Such systems are primarily in demand when a ready-to-use solution is required without having to develop electronics and software.

The FEM 1.03 RC and FEM 1.08 RC diaphragm metering pump systems come complete with built-in stepping motor and control electronics. The systems have two basic functions: in RUN mode a specified volume flow rate (volume/ time) is dispensed continuously; in DISPENSE mode the pump works intermittently. Both modes can be configured as required by adjusting the software parameter settings.

The range of OEM metering pumps is supplemented by portable designs for laboratories, trials, production and other such purposes. Irrespective of which product is used in any given case, the manufacturer can customize the equipment quickly and cheaply thanks to a modular design system.