Spray pumps are an extremely useful machine type and an excellent example of the basic principles of hydraulics. The spray bottle head consists of only a few parts. Has a trigger lever that activates a small pump. This pump is attached to a plastic tube that draws cleaning fluid out of the bottom of the tank. The pump pushes this liquid down a narrow barrel and brings out a small hole in the barrel of the gun. The hole or nozzle serves to concentrate the flowing liquid so that it creates a concentrated stream.
The only complex element of this design is the fluid pump and it is as simple as possible. The main moving element is the piston in the cylinder. There is a small spring inside the cylinder. To start the pump, pull the trigger back by pushing the piston into the cylinder. The movable piston compresses the spring, so when the trigger is released, the piston is pushed out of the cylinder. These two piston strokes, into the cylinder and outwards, constitute the entire pump cycle.
The stroke down, the piston retractable, reduces the area of the cylinder, pushing the fluid out of the pump. The up stroke, the spring pushing the piston back, expands the area of the cylinder, sucking fluid into the pump. In the spray bottle you have to suck the cleaning liquid out of the tank below and push it through the barrel above. In order for all the fluid to flow through the barrel, the pump only needs to force the fluid to flow upwards - it cannot force the liquid back into the tank. In other words, the fluid must flow through the pump in one direction only.
The device that makes this possible is called a one-way valve. The spray bottle has two non-return valves in the pumping system: one between the pump and tank and one between the pump and nozzle. Typically, the valve between the pump and the tank consists of a small rubber ball that rests neatly in a small gasket. The sides of the seal are angled so that the ball does not fall. Depending on the design, gravity or a small spring holds this ball against the seal so that the water channel is blocked when you are not pumping. When the piston extends (after releasing the trigger), the expanding area of the cylinder sucks in the fluid below, pulling the ball out of the seal. Because the ball is lifted, fluid can flow freely from the tank. But when you press the trigger, the external force of the moving fluid pushes the ball into the seal, blocking the passage to the tank. Consequently, the pressurized fluid is only forced through the barrel.
In the spraying mechanism described above, the one-way valve between the pump and the nozzle is a kind of cup that fits the end of the barrel. During the upstroke, internal pressure from the pump draws the cup to the cylinder, so air cannot flow through the nozzle. During the down stroke, the ejecting fluid slightly raises the cup from the cylinder and flows through the nozzle. Without this second one-way valve, the pump system would not be able to draw fluid from the tank because there would be no suction (no drop in air pressure). A jump up would not lower the air pressure in the pump; it would only hold the pressure.
This valve also works as a shut-off system. After screwing in the nozzle element, it presses the valve cup firmly against the cylinder so that no liquid can be pushed out. After loosening the nozzle element, there is enough space for the valve cup to move forward and backward.
When you use the spray bottle for the first time, you must press the trigger several times to spray the cleaning liquid. There are two things that cause this delay:
Before pumping, the gun is set to move down instead of up (the piston sits outside the cylinder). When you first pull the trigger and the piston pushes in, you will not be able to pump the liquid out; there is only air in the cylinder chamber. The piston must extend to aspirate fluid from the reservoir.
During the first upward stroke, the pump starts to suck cleaning fluid from the tank. But it also draws air in the plastic tube leading to the tank. Before you spray a cleaning fluid, you must pass this air through the pump mechanism. It may take a few jumps up and down.
This simple pump design, called the piston pump, is used for various tasks. In addition to pressurized water, air and many other liquids, this design can also extract water and oil from the underground. We even have piston pumps built into our bodies: Your heart expands to draw low pressure blood through one way valve and contracts to push high pressure blood through another one way valve back into your body. The same basic mechanism that makes a regular spray bottle work is also used to keep you alive!
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