Isolation valve has novel "resilient" seal

Edited by the Engineeringtalk editorial team Mar 27, 2003

A new miniature inert solenoid valve uses a "resilient" Kalrez1 seal in an innovative and cost-effective design.

In the design of any analytical instrument one 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.

To address these leakage problems, Asco Scientific has developed a new miniature inert solenoid valve that uses a "resilient" Kalrez1 seal in an innovative and cost-effective design.

At the heart of any type of automated analytical instrument is the fluidic circuit.

This is designed to reduce the amount of repetitive manual steps required to analyse a substance.

It achieves this by automating the flow of various fluids, such as solvents, buffers, reagents, samples and cleaning solutions, through the analytical instrument.

Key to this automated operation is solenoid valves, which are used to select between different fluids, divert flow, and dispense fluid.

Solenoid valves are used because they are a relatively inexpensive way to electronically control fluid flow.

They are found in all types of analytical equipment, performing such operations as buffer selection in gradient systems, diversion of flow in fraction collectors, reagent handling/dosing, line rinsing, and waste removal in blood analysers, liquid and gas control in auto samplers, and the control of sample flow in electrophoresis.

A number of factors have to be considered when selecting a solenoid valve for applications in analytical instrumentation.

In addition to reliability, which is the most important of all, these include flow requirement, operating pressure, power consumption, material compatibility, port connections, and size constraints.

Also of importance are the valves flushing characteristics, repeatability, internal volume and cycle life.

One of the most common problems with miniature solenoid valves used in analytical equipment is internal seat leakage caused by particulate matter.

Solenoid valves in analytical equipment are typically subjected to many different fluids and, therefore, are required to have very inert wetted components.

Most of the inert solenoid valves on the market today use a PTFE diaphragm to isolate the fluid from the solenoid components and seal on the valve seat.

However, 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 Kalrez1 disc inserted into a PTFE diaphragm.

The PTFE diaphragm provides the rigid structure that isolates the fluid from the solenoid components and the Kalrez1 disc provides a very tight seal on the valve seat.

As Kalrez1 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 Kalrez1 disc means that it is not easily scratched by particulate matter, as is the case with a complete PTFE diaphragm.

Finally, if there is any particulate on the valve seat or deformation of the valve seat, the Kalrez1 disc will tend to conform around the particulate or deformation to provide a better seal than PTFE.

In addition to its resilient seal, the series 462 has been designed with other benefits to the analytical equipment design engineer in mind.

Since laboratory space is at a premium, the small size of the series 462 (25.4 x 37.65mm) saves valuable space in OEM equipment.

Furthermore, to reduce the chance of crossthreading that is common with PTFE valve bodies; the standard body material of the series 462 is Peek, which is a very inert and strong material.

The series 462 was also designed with a very low internal volume and good flushing characteristics to prevent crosscontamination and the waste of expensive solvent and reagents.