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Plural Dispensing Equipment - How it works
Pump Basics |
Gun Basics
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The LiquiMix® Plural Dispensing Equipment has two positive displacement, double acting pumps, driven
by a single air motor. The liquid pressure is comparatively low, ensuring longevity of the system. Parts A
and B are pumped to the gun where they are mixed and sprayed onto the job. Atomising air, liquid flow, air
flush and solvent flush are all controlled at the gun. The system uses external or internal air atomisation.
Parts A and B are mixed at the tip of the gun by a static mixer. At the end of each operation the gun is
easily flushed using a small amount of solvent.
Pump Basics
- Foot Valve: The materials are drawn into the foot valve of the pump from the supply hoppers. The foot
valve is screwed into the bottom of the pump, making removal for inspection of the ball and seat a 5-minute
job. The seat is made of hardened tool steel to ensure long lasting and trouble free operation.
- Positive Displacement: Because both pumps positively displace exactly the same volume for each stroke
and both are tied together and driven by the one air motor, the integrity of the mix ratio is guaranteed.
Liquid is pumped during both the up stroke and the down stroke. LiquiMix® pumps have a longer than normal
stroke length to give greater efficiency and longer life. When the piston changes direction at the top and
bottom of each stroke, the resulting drop in pressure, or "surge", is virtually eliminated by specially
designed "surge chambers".
- Piston Rods: The piston rods are made of hard-chromed steel and contain the valve system for the double
acting mechanism of the pumps. This internal valve is spring loaded to ensure a positive and rapid seal at
the change of direction of travel. This virtually eliminates the possibility of any slippage of material
thus helping to guarantee the integrity of the mix ratio of part A and B.
- Cylinders: The cylinders are machined and honed to exacting tolerances.
- Seals and Cups: Different piston seals are used in each pump, reflecting the different chemical and
physical qualities of parts A and B. The seals can be replaced in both pumps in minutes without having to
dismantle the entire pump. A special Molybdenum impregnated nylon is used to secure the seals in place. The
piston cups are made of high quality high-density nylon.
- Air Motor: A single "intelligent" air motor drives both pumps. It is "intelligent" because it has the
following features:
- Fully adjustable stroke length
- Fully adjustable cushioning for top and bottom of stroke
- Air flow can be controlled at either the inlet or the exhaust or both
- A built in magnetic sensor can send an electric or pneumatic signal to anywhere on the unit or even to a remote monitor
- The unit can be controlled remotely by a computer for production use in a factory
- The operation is very quiet
An air regulator and pressure gauge allows the operator to fully control the air pressure to the air motor. This
in turn determines the flow rate and pressure of the liquids being pumped. The length of stroke of the air
motor can be infinitely varied in seconds. This feature may not be needed in most continuous spraying
operation, however it can be used to adjust the volume per stroke of both pumps. This feature allows a
stroke counter to be accurately calibrated to liquid volume output per stroke. Being able to adjust the
air flow at the exhaust allows greater torque to be delivered to the pumps.
- Recycle of Materials: When the unit is first started it is useful to be able to recycle material through
the pumps to make sure that everything is working properly and to adjust the inlet air pressure using the
regulator and pressure gauge. Both parts A and B can be recycled together or individually. Individual
recycle of one part is used to avoid wastage when the correct flow of the other part needs to be checked
through the gun.
Plural Dispensing Equipment - Pump View
Gun Basics
- Material Inlet: The two materials don't mix until they have traveled through the gun and into the static
mixer tube. Delivery of part A & B to the static mixer is by way of 2 valves operated by a trigger.
- Static Mixer: LiquiMix®'s innovative alloy pre-mix nozzle ensures that parts A & B don't mix until they
are actually right in the static mixer tube. Once in the stainless steel tube the two parts are mixed by
the plastic mixer elements until they become homogenous. They are then forced through the fluid nozzle
and Atomising air is introduced to create a spray pattern. The LiquiMix® pre-mix nozzle is unique because
it allows the operator to quickly change from one sized static mixer element to another. The elements can
be used either in the LiquiMix® tube or they can be used in their own plastic tube and bell housing. The bell
housing fits snugly over the end of the pre-mix nozzle and acts as a gasket or seal for the static
mixer-retaining ring. The Solvent flush feature ensures that the static mixer elements can be used over and
over again, eliminating the costly replacement of elements every time a new operation is started. However,
if the operator prefers not to use any solvent, the elements may simply be replaced for each new operation.
Elements diameters are available in size 6.3mm, 8.0mm and 9.3mm.
- Solvent Flush and Air Purge: Solvent is stored in a pressurized stainless steel pot at the main unit.
From there it travels to the gun along a tube bundled together with the other tubes for the materials and
air supply. A quick flick of the valve at the back of the gun is all that it takes to flush the mixing
elements. About 100ml (1/2 cup) is used per flush. After solvent flushing an air purge can be blasted through
the mixer tube to remove most of the solvent.
- Spray Configuration: The flow rate of both the liquid and the atomizing air can be controlled
independently of each other. Furthermore, a wide combination of spray set-ups is available. This allows
the operator to have full control of the fluid delivery rate and spray pattern to suit each job. To change
from one set-up to another takes less than 60 seconds. The following spray patterns can be achieved.
- Round spray: An extended full cone round spray pattern.
- Wide-angle round spray: A hollow cone-type, wide angle round spray pattern.
- 360° circular spray: A hollow cone type 360° circular spray pattern.
- Flat spray: An extended flat or sheet-type spray pattern.
- External Atomisation: This method means that the liquid and air streams meet outside of the nozzle. This
is effective for higher viscosity liquids. Air and liquid flow can be controlled independently. It is
therefore possible to increase or decrease the atomisation of the liquid without affecting its delivery
rate onto the job. Furthermore, external air atomisation reduces the amount of fumes and airborne particles.
This allows most Urethanes to pass local pollution laws. External mix can only produce a flat spray.
- Internal Mix: Internal air atomisation means that the liquid and air are mixed inside the spray nozzle
to produce a completely atomised spray. The liquid and gas streams are not independent and a change in
airflow will affect the liquid flow. Internal mix produces a finer spray than external mix but increases
the amount of airborne particles.
- Hoses: The material hoses transporting Part A and Part B to the gun can be up to 50m in length. Using
special lightweight hoses makes it easy to unwind and take onto any job site
Plural Dispensing Equipment - Gun View
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