Whilst component performance, size and cost are obvious considerations
in the selection of vacuum pumps, these rather bland descriptors can
represent only the tip of the iceberg. Warren Beese looks below the
surface to reveal far-reaching design implications
Reducing weight, improving handling, expanding applications, gaining
production efficiency and saving space and energy are all important
engineering considerations in the design and development of consumer,
commercial and industrial products. The application scope of products
such as vacuum pumps is enormous. Within a whole host of medical,
environmental, automotive, aerospace and many other products, pneumatic
systems such as vacuum pumps and compressors are mission-critical
components, and increasingly in their initial selection they are being
treated as such.
Working in miniature
Whilst the glamour of any new design often seems to be focused on the
miniaturisation of electronics components and microchips, it is most
often the workhorse components which are the real key to a product's
success or failure. With pneumatic system size ultimately limited by the
laws of physics, core components like vacuum pumps are never going to
enjoy quite the same breathtaking headlines as the electronic devices
that share space in the overall product package. That said, innovations
in vacuum pump design have led to dramatic reductions in size which can
enable OEMs to realise significantly smaller product design envelopes.
There are no 'one-size-fits-all' solutions with miniature pumps, with
designers offered a wide range of choices including diaphragm, piston,
rotary vane, vibrating armature, diaphragm and peristaltic pumps.
Selection of the right pump has to be defined by the specific
application. In medical devices, diaphragm and rotary vane pumps are
common choices. Both operate with low electromagnetic interference motors
and offer optimal speed control with minimal torque sacrificed. Both
offer a wide range of pressures and flows. Diaphragm pumps are tighter,
leak-proof and provide greater vacuum/pressure without contaminating a
medium. The rotary vane design provides a smooth, pulse-free flow, but
the transported media is in direct contact with the pump vanes which
increases the potential for contamination. Rotary vane pumps do, however,
offer ultimate potential for miniaturisation.
Vibrating armature pumps are preferred for continuous duty applications,
when pump longevity and zero-contamination risk are important. However,
these ac pumps are less compact than other miniature pumps. Piston pumps
are compact, and provide above average vacuums/pressures, but are not
leak-free.
The price is right
Component cost is always a consideration in the development of any new
product, but there can be much more to consider than the initial purchase
price. Meeting stringent demands for end product miniaturisation, for
example, can mean that pump modification is necessary. Similarly, a
product upgrade can necessitate significant system design changes which
can require alternative pump mounting strategies, orientation and other
design tweaks. Whilst these modifications can undoubtedly be achieved by
the OEM, they can often more easily be accommodated by the manufacturer,
providing cost savings in the longer term even though the purchase price
might be slightly higher.
Cost is also becoming an issue in industries that have traditionally
enjoyed a certain flexibility in their end product pricing. The medical
industry, for example, had few incentives in the past to disclose product
cost objectives to the likes of pump manufacturers. Now, target price
objectives have become crucial in product development, with neither the
pump manufacturer nor the OEM product designer able to ignore the
volatile economic and technical forces in today's market.
Early dialogue with the pump suppli