4
General Principle of Pressure Washers.
Pressure in Spray Master Technologies and most other pressure
washers is produced by forcing a fixed gallons per minute
(GPM) volume of water through an orifice. The fixed volume of
water is provided by a positive displacement pump, which will
produce a specific GPM of water flow regardless of the operating
pressure. The orifice is a part of the nozzle on the end of the
Theory of Operation - Mechanical
Figure 1.
Simplified SMT Central Pressure Cleaning System
The water supply source to the system must provide a minimum
flow of five gallons per minute at 30 PSI, and should be filtered
through a high quality filter to eliminate contaminates that will
cause wear and shorten the life of the pump. The output from the
filter enters the float tank through one or two float valves within
the tank. The float tank maintains a minimum water source for
the pump and is monitored by the float switch. If the water level
falls below the float switch, the system is disabled to prevent
damage that would occur from running the pump dry.
When the pump is in operation, it draws water from the float
tank and pumps it out to the unloader assembly. The unloader
assembly directs the water through the system to the spray gun
if the spray gun is open, or it diverts the water back to the float
tank, through the re-circulate path, if the spray gun is closed. In
addition, the unloader is used to set the maximum operating
pressure of the system.
From the high-pressure output of the unloader, the water flows
through the chemical inhibit flow-switch, past the bleeder valve
assembly to the interconnecting high-pressure tubing and out to
all the remote stations. The pump can service up to ten remote
stations. Each remote station is equipped with a quick-connect
port for connection of a high-pressure hose.
spray gun. The volume of water and the orifice size can be varied,
resulting in a corresponding change in the operating pressure
of the system. The following paragraphs explain the function of
system components and flow sequence in SMT pressure cleaning
systems. This brief theory of operation will provide a service tech
with information necessary to quickly diagnose and correct any
malfunction of the system.
Water Flow
Refer to Figure 1, Simplified SMT Central Pressure Cleaning
System, for the following discussion. The key plumbing
components of a basic SMT Central Pressure Wash System
consists of
1) water filter, 2) water supply float tank, 3) float
switch, 4) pump, 5) unloader valve, 6) chemical inhibit flow
switch, 7) bleeder valve, 8) interconnecting hi-pressure tubing, 9)
remote stations, 10) hi-pressure hose, 11) spray gun/nozzle, 12)
line pressure release valve and 13) thermal limit switch.
From the remote station, the water flows through the hose to
the spray gun. The water passes through the spray gun when
the gun-trigger is activated and flows to the nozzle at the end of
the lance. As the water is forced through the orifice in the nozzle,
pressure builds within the system. The size of the orifice in the
nozzle determines the maximum pressure that can be achieved
with the flow rate provided by the pump. The smaller the orifice,
the higher the pressure. Most SMT systems are equipped with a
dual nozzle selector and two nozzles. The nozzle with the small
orifice will produce high pressure, while the nozzle with the large
orifice produces low pressure.
Note: Selecting the correct nozzle size
for the system is critical to the correct
operation and cleaning effectiveness.
A nozzle with too small an orifice will
result in less water flow and reduced
cleaning effectiveness and may result
in too high pressure, overloading the
motor. A nozzle too large will result in
lower pressure and reduced cleaning
effectiveness.
During operation, when the spray gun trigger is released,
pressure builds in the system until it overcomes the tension on
the unloader spring and activates the unloader assembly. When
the unloader assembly is activated, it locks pressure into the
output line to the spray gun and redirects the flow of water, at
low pressure, through the recirculate line back to the system float
tank. Recirculation will continue until the line pressure is reduced
by reactivating the trigger on the spray gun. This unloading
feature prolongs the life of the pump and motor by removing the
strain on the pump and motor during periods when the spray
gun is inactive.