The hooded Bottle Pump Head is a very useful device, and it is an excellent example of the fundamental principle of pipe pumping. The head of the hooded plastic pump head consists of only a few parts. It has a trigger that triggers a small water pump. The pump is connected to a plastic tube that draws cleaning fluid from the bottom of the reservoir. The pump presses liquids into a narrow cavity and ejects them through small holes in the sprayer tip. This orifice, or nozzle, can bring the moving liquid together into a concentrated stream of water.
 
Only one complex in this design is a hydraulic pump, but its layout is also very simple. Its primary moving element is a piston, which sits in a cylindrical hydraulic chamber. In the hydraulic chamber, there is a small spring. In order for the hydraulic pump to work, you first pull the wrench back and then push the piston into the hydraulic chamber. The moving piston compresses the spring so that when you release the wrench, the piston is pushed out of the hydraulic chamber again. The two strokes of the piston in and out of the hydraulic chamber constitute a complete pump cycle.
 
During the downstroke, the piston is pushed inward, compressing the volume of the hydraulic chamber, which then forces the fluid out of the pump. On the upstroke, the spring pushes the piston outward, expanding the volume of the hydraulic chamber, which then draws fluid into the pump. When using a hooded plastic pump head, you need to suck the cleaning fluid up from the reservoir below and squeeze it out of the cavity above. In order to get all the liquid flowing into the cavity, the pump can only press the liquid up - not the liquid back into the reservoir. In other words, the liquid can only flow through the pump in one direction.
 
The device that accomplishes this function is called a one-way valve. The hooded plastic pump head has two one-way valves in its pumping system: one between the pump and the reservoir and the other between the pump and the nozzle. Typically, the one-way valve located between the pump and the reservoir consists of a small rubber ball that is lightly placed in a small sealed cartridge. The edge of the sealing tube has a sharp edge, so the rubber ball will not fall from the sealing tube. According to the design, when you are not pumping water, the small ball relies on its own gravity or the elasticity of a small spring to press against the sealing cylinder, and then block the passage of water. As the piston moves outward (when you release the wrench), the expanded hydraulic chamber draws the small rubber ball away from the sealing barrel, drawing the liquid up from below. Because the pellet is lifted, the liquid can flow unimpeded from the reservoir. When you depress the wrench, the force of the active fluid pushes the ball back onto the seal, blocking the passage between the pump and the reservoir. Therefore, the pressurized liquid can only flow to the small cavity above.
 
The one-way valve located between the pump head and the nozzle is a cup-shaped device that is placed at the end of the cavity. During the upward stroke, because the pressure inside the pump is less than the outside air pressure, the cup-shaped device is pulled tightly against the cavity, so air cannot flow in from the nozzle. On the downstroke, the forced liquid pushes the cup-shaped device finely away from the cavity and out of the nozzle. Without the second check valve, the pump system would not be able to pull liquid up from the reservoir due to lack of suction (no air pressure drop). At this point, the upstroke doesn't drop the air pressure in the pump; it just sucks in more air to maintain the pressure inside the pump.
 
A second plastic pump head check valve can also be used as a shut-off system. When you screw on the spray head, the cup valve is pressed against the cavity so that no liquid can be forced out. When you unscrew the spray head, there is ample room for the cup valve to move back and forth.