Product category:
Valves and manifolds
News Release from: ASCO Joucomatic | Subject: Specialist solenoid valves
Edited by the Processingtalk Editorial
Team on 13 September 2006
New developments in solenoid valves
New developments in solenoid valve products are benefiting users in medical, biomedical and analytical equipment, with inert resilient sealing, and piezoelectric technology for low power operation
Everyday, new types of machines and equipment are being designed and developed that push the boundaries of medical science forward In this continuing offensive, specialist medical, biomedical and analytical valve products are playing a key role
This article was originally published on Processingtalk on 20 Sep 2006 at 8.00am (UK)
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In the design of any analytical instrument (HPLC, GC, sample prep, DNA/protein sequencer etc) some of the most critical components to consider are the solenoid valves used to control fluid flow.
These must be free of the problems of leakage that can cause instruments to produce inaccurate analysis results.
However, most of the inert solenoid valves on the market today use a solid PTFE diaphragm for sealing, which has inherent leakage problems.
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As PTFE is not a very resilient material, it does not have good sealing characteristics and is very susceptible to scratching from particulate matter.
The problem with scratching is that it can create a leak path across the valve seat allowing fluid to flow in the closed position.
This leakage will cause the instrument to produce inaccurate results.
A new development by Asco Scientific greatly reduces the possibility of seat leakage in solenoid valves due to the action of particulate matter.
The development is an inert isolation valve (series 462) that uses a 'resilient seal' against the valve seat.
The series 462 uses a soft Kalrez disc inserted into a PTFE diaphragm.
The PTFE diaphragm provides the rigid structure that isolates the fluid from the solenoid components while the Kalrez disc provides a very tight seal on the valve seat.
As Kalrez is an elastomer, it has excellent sealing characteristics.
It is also a very inert material; therefore it is compatible with the majority of solvents and reagents used in analytical instruments.
In addition, the resilient nature of the Kalrez disc means that particulate matter does not easily scratch it, as is the case with a complete PTFE diaphragm.
Finally, if there is any particulate material on the valve seat or deformation of the valve seat, the Kalrez disc will tend to conform around the particle or deform to provide a better seal than PTFE.
In addition to difficulties with sealing, another common problem that can spoil the accuracy of medical and analytical processes is heat transfer from a valve to the fluid medium that it is controlling.
This problem occurs when conventional solenoid operators with relatively high wattage coils are employed.
However, it can be overcome using piezo technology, as employed in the Asco Scientific new Piezotronic proportional valve.
The new Piezotronic valves use CMA (ceramic multilayer actuator) technology, which gives response times as low as 100us, a practically unlimited service life (of greater than 1 billion cycles) and, crucially, extremely low power consumption at just 0.3mA at 24V (0.007W) and 0.9mA at 70V.
This means that there is no heat transfer from the valve into the fluid being controlled.
The CMA technology employed by the Piezotronic valve comprises a monolithic piezoceramic strip with integrated electrodes that are specially configured so that the element 'bends' when a voltage between 20 and 40V is applied.
This bending action, which involves no moving parts, is key to providing the precise levels of proportional control demanded in such applications as gas analysis and the micro-injection of aqueous solutions into living cells.
The fact that there are no moving parts in the operation of the Piezotronic offers several benefits: first, response times are exceptionally fast, 100us typically.
Secondly, service life is practically unlimited at around one billion cycles.
Thirdly, the unique operation of the Piezotronic valves also means that there are no inductive peaks when switching, so unlike conventional solenoid valves, no circuit protection is necessary.
Finally, no holding current is required for the valves to maintain position, so heat generation here is not a problem.
As well as overcoming actual operational problems that can adversely affect equipment performance, valve suppliers to the medical and analytical sectors are also increasingly required to provide the longest reliable life possible to optimise equipment costs.
In common with all areas of technology, manufacturers in the medical, biomedical and analytical sectors are looking for products that they can effectively 'fit-and-forget'.
The key to achieving this objective is a new design, such as the flat spring technology employed on the Series 065 valves, from Asco Scientific: these provide an operating life of 1 billion cycles when used with neutral gases.
The flat spring technology combines both valve spring and core functions in a unique flat part manufactured from a special stainless steel.
The result is a highly compact no-maintenance valve with only one moving part; a design, which, with no loss of core material due to friction, offers both high levels of process reliability and also integrity of the fluid controlled.
Intended for the control of gases and liquids, and vacuum (0.1bar abs) in the temperature range from 0 to 60C, the Series 065 valves are AISI 303 stainless-steel-bodied units with internals also of stainless steel, and seals and discs of high-performance FPM (fluoroelastomer/viton).
This construction ensures the widest range of chemical compatibility, a feature that can be extended with the option of Kalrez (FFPM) seals for aggressive fluids. Request a free brochure from ASCO Joucomatic ...
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