Heres an illustrated version of what Broomer describes -
venturi effect.
This article describes the use of a beckettvalve(a 4 holed venturi) in a skimmer design, but
check out the bottom of the article in the explaination box, it goes into detail about how the reduction in pressure occur, andhow the water jet is formed.
here is a snippet of the explaination
"The familiar traditional venturi valve has a single air intake (called a pitot tube). Essentially, pressurized water enters the injector inlet, it is constricted (by passing through a restriction) toward the injection chamber and changes into a high-velocity jet stream. The increase in velocity through the injection chamber results in a decrease in pressure in the injector body. When a sufficient pressure difference exists between the inlet and outlet ports of the injector, a vacuum is created inside the injector body, which initiates suction through the suction port. At this point air is literally sucked into the vacuum space. As the jet stream is diffused toward the injector outlet, its velocity is reduced and it is reconverted into pressure energy (but at a pressure lower than injector inlet pressure), and the "microbubbles" are produced."
bottom line, when too much backpressure exists to force the water forward, it goes out the air intake hole.This will often happen when the water level in the skimmer gets too high, and the pump can't push hard enuf againist the water
frank
