In June 1990 a USA consultancy firm
predicted that sealless gear pumps would
take an increased percentage of the
market – “probably 25% by 1995 and 50% by
2000”. That didn’t happen.

The technology at that time was not
reliable enough, with too many instances of
failures that were brought about by excessive
bearing loads and design deficiencies that led
to breakdown and leakage issues. These
failures created a stigma that many
manufacturers of sealless pumps are still
trying to overcome today.

Adopting a fresh, clean-sheet approach to
confronting the conundrums inherent in
traditional sealless pump design has led to
the creation of a new line of sealless gear
pumps. The new Envirogear pump (Fig.1)
increases reliability while eliminating the
unacceptably high ownership, maintenance
and environmental costs that have dogged
many previous sealless gear pump designs.

With its simple design comprising seven
primary parts, the Envirogear pump is
designed to eliminate all the operational
concerns found in old-style sealless gear
pumps. The leading causes of high
maintenance in conventionally sealed pumps
include those associated with mechanical
seal replacement and the premature wear of
the bushings and close-fitting metal parts
due to insufficient support of the rotating
pumping elements.

There are also the environmental costs of
leakage include cleanup, possible forced shutdown
and environment hazard fines and
penalties, plus the resulting bad press and
community mistrust if a leak or accident occurs.

Times have changed (and so have
sealless pumps)

Traditional sealless gear pumps are designed
with a cantilevered load where a large rotor
gear is attached to the end of the pump shaft.
As hydraulic force is applied to the rotor during
pump operation, extra pressure is put on the
shaft and bearings. This pressure can lead to
shaft deflection and increased bearing wear,
which results in more rotor-to-casing or
rotor-to-head contact wear. The result is
rapid loss of pressure and flow performance.

Secondly, traditional sealless gear pumps
feature a magnetic drive chamber and a fluid
pumping chamber which are joined together.
These elements result in a long, complex pump
with elongated, narrow flow-paths and the
need for more components, which may make
the pump more expensive and difficult to
maintain. This also limits the viscosity of the
liquids that can be pumped.

What to change?

The first step is to identify the areas in which
sealless pumps fall short then look for
improvements. Traditional sealless pump
bearings are severely affected by the pump’s
cantilever load. It was important to find a
superior replacement for the classic magdrive
two chamber design that complicates pump
operation and limits fluid handling capabilities.

The Envirogear pump features two design
enhancements to overcome these challenges.
These enhancements are:
Between-the-bearing support systems – As
opposed to the performance-robbing, onesided
support found on the cantilevered load
design that exists in traditional sealless pumps,
the new gear pump supports the rotor and
idler gears at three locations. This is achieved
through the creation and incorporation of

•  A patented eccentric spindle (Fig.2) that is
  supported in the head, the crescent location
  and the back of the containment canister,
  eliminating much of the cantilever load.
•  Large diameter journals that provide more
  rigid support for less shaft deflection and
  bearing wear.
•  Large, long radial bushings that support
  the entire length of the rotating element,
  which spreads out the hydraulic forces and
  gives extended operational life.

One fluid chamber design – The improved
design has only one fluid chamber with the
pump’s magnets piggy-backed on the rotor
gear element. This design gives the pump a
much shorter, simpler flow-path. It also
allows the pump to easily handle solvents or
liquid viscosities up to 30,000cP.
Envirogear pumps have dimensional
interchangeability with 95% of the other
internal gear pumps that are currently available.
A plant can run a traditional sealed pump in the
morning and have it pulled out in the afternoon
and drop the single fluid chamber Envirogear
pump into the footprint while reusing the
same piping, gearbox, motor and base plate.
For more information visit
www.axflow.com