Pinch valves provide precision and reliability

Edited by the Engineeringtalk editorial team Oct 31, 2003

Used extensively for microbiological sampling in the food, water, dairy and public health sectors, the unique Whitley automated spiral plater uses silicon tube pinch valves from Asco Scientific.

The WASP (Whitley automated spiral plater) range of spiral platers, designed and manufactured by Don Whitley Scientific, lead the world in precision, speed of sampling and reliability.

Used extensively for microbiological sampling in the food, water, dairy and public health sectors, the unique WASP units employ silicon tube pinch valves from Asco Scientific.

These valves allow connection very close to the plater's automated syringe, thereby controlling any possible error in the sample size, which might be caused by flexing in the tube.

The Asco valve also provides positive shutoff for the sampling process, ensuring zero weepage to protect against sampling inaccuracies.

Developed in Shipley, West Yorkshire, the WASP is a means of making traditional microbiology much simpler and quicker.

Designed very much with the user in mind, the WASP represents a radical new approach to plater design, introducing automation, repeatability and flexibility into spiral plating.

The success of this approach is evidenced by the extensive use of WASP spiral platers in markets all over the world, including the USA where sales exceed GBP 1 million.

The machines are used extensively in the food industry to test for safe levels of bacteria and are also employed in non-food sectors such as pharmaceuticals, cosmetics, water and in the medical/analytical sector to test for mouth and skin bacteria.

Such widespread use is testament to the many benefits provided by the WASP operating method when compared to conventional laboratory procedures.

These include minimal set up time, the elimination of serial dilutions, up to 69% labour saving, a reduction in consumable costs and laboratory waste with up to a two-thirds reduction in incubator space requirements.

At the heart of the WASP is a microprocessor to control all aspects of the deposition of a liquid sample onto the surface of a rotating agar plate (a shallow, circular disposable petri dish).

Also integrated is a unique stylus arm that dispenses liquid samples in an Archimedes spiral, either uniformly across the agar plate, or as a continuous decreasing volume (equivalent to a thousand-fold dilution).

Preprogrammed options allow the liquid sample to be dispensed in a variety of ways, using up to 400ul of sample.

In all cases the design of the WASP is distinguished by its ability to load, sample, inoculate a plate and then clean the stylus with a single keystroke.

The high level of automation employed on the WASP contrasts with the previous generation of spiral platers, which were electromechanical units employing a cam to produce the pattern on the agar plate.

However, what the two machine types do have in common is that both use Asco pinch valves.

Before its unique WASP design, Don Whitley Scientific used to market electromechanical machines under licence from the USA.

These proved their reliability in the field over extended periods equipped with the Asco/Angar range of two-way pinch valves.

As a result, when DWS developed its own unique design - and sold it back to the Americans - the valves employed were once again from Asco Scientific.

"Its difficult to find a valve any more suitable to do the job", commented Evan Kitsell, Design Manager, at Don Whitley Scientific.

"When designing instrumentation we have to take a long term view, because our customers demand many years of excellent trouble-free service.

The number of our machines operating reliably in the field is evidence that we satisfy that demand, which is testament both to our basic design and to the quality of Asco Scientific valves".