About Westech 8 Stage Impactors

About-Westech-8-Stage-Impactors-About Westech 8 Stage Impactors Westech 8-stage non-viable cascade impactors are the result of many years experience in the design and manufacturing of similar devices. The team at Westech in collaboration with Dr Steve Nichols, then of Rhone Poulenc Rorer, were responsible for the design, configuration and validation of the 60 L/min and 90 L/min versions of the standard 28.3 L/min 8 stage impactor which has gained a significant reputation in the measurement of particle size distribution in the testing of pharmaceutical inhalers.

This experience has allowed Westech to produce extremely high quality impactors with ever improving specifications and tolerances to meet the increasingly stringent requirements of both the pharmaceutical industry and its legislators.

wdk i075 3wdk i030 1imps1 160etail specification

Cascade impactors are multi-jet, multistage devices operating at constant flowrates that allow the characterisation of an aerosol in terms of its particle size distribution. (see Technical Focus – Impactors: How they work...) Westech produces three main configurations of the 8-stage non-viable impactor - designed for flowrates of 28.3, 60 and 90 L/min - and all are available in a variety of materials including Aluminium, 316 Stainless Steel and Titanium.

Conversion kits for 60 and 90 L/min allow the standard 28.3 lpm impactor to be upgraded to the higher flowrates. Recently trials have been undertaken on a Delrin version running at 15 L/min validating both the performance of an impactor constructed in Delrin and the cutpoints at the lower flowrate. Westech 8-stage impactors have been designed to give approximately equivalent cutpoints at similar stage positions in the stack and these are outlined in the table below.

Flowrate Configuration 28.3L/min 60L/min 90L/min
D50 Cutpoint in microns (µ) D50 Cutpoint in microns (µ) D50 Cutpoint in microns (µ)

All these cutpoints have been independantly, traceably verified by a UKAS (United Kingdom Accreditation Service) certified laboratory including those of the peseparators used when testing Dry Powder Inhalers (see "8-stage Impactor for DPIs"). All Westech 8-stage Non-Viable impactors are quality controlled to extremely high tolerances by the use of a vision inspection instrument - Impactor Vision Inspection System (IVIS). Developed by Westech personnel (in conjunction with Specac Ltd, UK) this unique instrument is specifically designed for the measurement of the area, diameter and shape of the jets of Westech impactors. Our history in the development of the 8-stage impactor gives us an unrivalled, intimate knowledge of the precision required to produce impactors with a guaranteed 100% of all jets being significantly within the required tolerances laid down in the various pharmacopiea.