Theory Of Operation; Use; Major Components; Ratio Proportioning - Graco 8900 Instructions For Use Manual

Theory of Operation

Theory of Operation

Use

The 8900 Proportioner is used with two component
materials where one or both components is high viscos-
ity. This is typically found in the sealant and adhesive
industry, where special requirements for loading and
pumping necessitate the use of the 8900 proportioning
system.

Major Components

The major components of the 8900 Proportioner system
include the:
• Component A or major volume metering cylinder
• Component B or minor volume metering cylinder
• Component A or major volume feed supply
• Component B or minor volume feed supply

Ratio Proportioning

The A and B cylinders are positive displacement meter-
ing cylinders. Positive displacement cylinders displace a
defined volume of fluid for a given stroke length.
On fixed ratio units, the volumetric ratio is the ratio of the
area of the component A displacement cylinder to the
area of the component B displacement cylinder. At a 1:1
ratio, the displacement cylinders are the same size. On
higher ratio units the component A cylinder is usually the
larger of the two. The ratio of the components is the dif-
ference in effective area between the cylinders.
On variable ratio units, the component B cylinder has an
adjustable stroke length. The component A cylinder has
a fixed stroke length. By setting the stroke adjustment to
different points on the connecting linkage, you can
change the stroke length of the B cylinder, which
changes the mix ratio. You can calculate the material
mix ratio from the ratio of the cylinder displacement vol-
ume.
Note that the mix ratio of the 8900 Proportioner is
achieved by volumetric ratio of component A to compo-
nent B and not by weight. These two ratios are often dif-
ferent depending on material properties.
6
System Components and
Operation Overview
Feed Systems - Feed Pumps
Load the Feed Pumps and Proportioner
The A and B feed pumps/cylinders must completely fill
(prime) on both strokes to ensure accurate material dis-
placement.
With high viscosity materials, it is difficult for material to
flow into the pump. Individual feed pumps are used to
supply these materials under pressure to the 8900 Pro-
portioner. When air is trapped in the feed system due to
improper loading, a condition called cavitation occurs.
If cavitation occurs, part of the downstroke will be used
to fill the vacuum before any material is actually dis-
placed. Since the total stroke length is used to calculate
mix ratio, this may result in an off-ratio condition.
To prevent cavitation with higher viscosity materials,
both cylinders are pressure fed. The A pump is pressur-
ized by a pneumatic ram supply unit applying a down-
ward force on a 55-gallon plate fitted into the drum. A
shovel action pump fluid inlet further aids in pump prim-
ing. Component B is delivered to the B pump by pres-
sure fed 5- or 55-gallon supply modules, depending on
the volumetric ratio of the material.
Pneumatic ram assisted feed pumps may not be
required for lower viscosity materials.
Feed Systems - Alternative Feed Supplies
Header or other feed systems may be used to supply A
and B materials to the 8900 Proportioner. Generally
these feed systems are provided by others and are not
addressed in this manual. This manual applies only to
the Graco Configured 8900 Proportioner system.
309790ZAF