Airless sprayers are mainly defined by three main categories:
1) Diaphragm Airless Sprayers
airless sprayers use a hydraulic piston to draw hydraulic fluid from the
sump and then compress the hydraulic fluid under a plastic diaphragm. The
diaphragm pulses up and down causing the suction valve above the
diaphragm to open and close which creates enough suction to draw paint
product through the suction hose. Once the paint has passed through the
suction valve it enters the outlet valve which usually contains a ball
and seat or check valve. This allows the paint to exit the outlet valve
but does not allow pressure in the hose to push back through the outlet
airless sprayers are controlled by a pressure control valve which
regulates the rate of which the hydraulic fluid is released from the
piston block back into the oil sump.
airless spray pumps can be driven by AC Electric motors and
petrol/gasoline motors with a simple eccentric bearing on the end of the
crankshaft, the bearing pushes the hydraulic piston up and down
compressing hydraulic fluid under the diaphragm.
airless pumps are more common in countries that use 220/240v power such
as Ireland, Germany, Japan, China and Australia to name a few. In
countries where the power grid only supplies 110v, diaphragm airless
sprayers have only been popular in low capacity machines.
airless sprayers are a simple mechanical type of airless sprayer that
they will deliver paint out of the spray tip in exactly the same fashion
as a piston airless sprayer.
Piston Airless Sprayers
airless sprayers use a double acting pump in order to draw the paint
from a container, this double action allows the pump to draw and
transfer paint at the same time by using an inlet valve (foot valve) at
the bottom of the pump and an outlet valve in the piston rod.
airless pump is running the fluid is transferred in a continues flow
through a small hose usually to a high pressure filter fixed to either
the pump and motor or frame of the airless sprayer, this filter traps
any small particles of debris or rubbish in the paint that could
potentially block the airless spray tip.
pressure of the airless sprayer is regulated by an electronic sensor
that tells the motor when stop and start according to either the
pressure selected by the operator or the maximum pressure setting
default of the computer. Piston airless sprayers these days have complex
computer boards that not only tell the machine when to stop but they can
also adjust the speed of the motor depending on the size spray tip
selected by the operator.
Piston airless sprayers are driven by DC Motors, although these motors
are light and produce high torque they require more components than a
diaphragm machines such as computer boards, pressure sensors and
electronic pressure control. Piston machines are very popular in the USA
because the DC Motors used can produce more power on a lower power grid
such as 110v.
3) Pneumatic or Air Driven Airless Sprayers
Piston airless sprayers use a double acting pump in the same manner as
electronic piston airless sprayers but the drive unit is an air driven
motor. Air driven motors are a simple reciprocating motor that works on
basic resistance of the air pressure in the motor versus the pressure in
the fluid pump.
airless sprayers are usually classed by the ratio of the air pressure
fed into the pump air motor which determines the fluid pressure that
flows out of the pump. To give an example of how this ratio is applied
to the size of the pump, see below:
Pneumatic Airless Sprayer
Pressure 30psi for every 1psi of air pressure fed into the air motor. If
the air motor inlet pressure was regulated to 50psi, the fluid pressure
in the pump would be 1500psi (50psi x 30psi = 1500psi)
airless sprayers are used mainly for industrial type coatings were
possible electrical hazards exist such as in steel manufacturing or
applications were electrical supply is limited or not available.
Pneumatic airless sprayers are also useful for thicker industrial
coatings that require higher atomization pressure at the spray tip.
Electric piston machines do not exceed 3300psi but pneumatic airless
sprayers can spray up to 8000psi.