All about design of water feature fountains
Today we continue our in-depth look at how the nozzles most commonly used in architectural fountains work and focus on those based on water entrainment or air suction – the latter used to produce a foaming effect in the water jet.
Water-drawing Nozzles. Based on the Venturi effect, this nozzle uses the speed of the propelled water to draw water from the basin which is then mixed with the initial stream to form a much greater mass of water than before. Looking at the diagram in figure 23, the jet of water discharged out of the central pipe is seen to draw in the water around the pipe. This effect causes an under-pressure that draws water from the basin. The jet propelled through the pipe when mixed with the drawn water forms a large mass of water discharged over the nozzle. Read more
To clearly understand how this water-drawing nozzle works, imagine that the jet propelled out of the pipe "crashes" into a thick wall of water (Fig. 24). This crash breaks the water surface and draws the water along in the jet to form a cone-shaped body of water. Depending on how thick the wall of water is, the height and diameter of the conical jet of water varies. If there is no water above the pipe, there can be no entrainment and the nozzle works like a lance jet nozzle (Fig. 25). If the film of water is thin, a conical jet starts to form but with a small diameter (Fig. 26). As the wall of water becomes thicker, the conical jet increases in diameter and decreases in height (Figs. 27 and 28) . This reduction in height is due to the jet losing speed as it has to drag more water. If the thickness of the wall increases further, the jet eventually becomes a gush of water (Fig. 29).
The first outcome is that there has to be a means of controlling the water level in the basin of the fountain to prevent the diameter and height of the water jet from fluctuating. But as the jet falls back into the basin, it causes waves and the waves create continuous changes in the level and consequently a fluctuation in jet diameter and height. To avoid this effect, a wave-deterrent needs to be provides (later we will look at different available systems) but there are those who claim that fluctuating jets are more "lively" and dynamic.
Comparing simple lance jets to water-drawn jets, the second type is seen to create a greater body of water for the same feed rate than the first but with a lower height. Moreover, with the lance jets, we indicated how important it is that the jet exits in a laminar regime to achieve a crystalline appearance. With the water-drawing nozzle, the intention is the opposite, i.e. for the water to have a turbulent regime to produce a more frothy appearance. That turbulence is produced by the inner shape of the nozzles.
The Safe-Rain nozzle that produces a water-drawing jet is called the Cascade nozzle. Two different models are produced, the smaller (Fig. 30) ones made of machined cast brass while the larger size (Fig. 31) are made of stainless steel and brass.
Also based on the Venturi effect, this nozzle draws air instead of water, as in the previous case. If we analyze the diagram in Figure 32, the jet driven through the pipe is seen to draw air surrounding the spout and consequently causes a vacuum which causes outside air to enter through the upper inlet of the nozzle, which protrudes above the water surface in the basin. The mixture of water impelled through the spout with the air sucked in from outside produces a highly oxygenated and frothy jet. The greater the air suction and the more homogenously it is mixed with the water, the frothier the water jet will be and the greater its volume. The internal turbulence to achieve optimal water-air mixture is achieved by means of a ball (Fig. 33) which the jet of water hits as it runs through the inside of the spout. Shows a picture of a Safe-Rain nozzle made of colorless polycarbonate, in which clear water is seen to run out of the inner spout before hitting the ball and "turning into” bubbling and frothy water. The water jet produced by this type of nozzles is the one that mixes more air with the water and is therefore very suitable for increasing the life-span of the water before it becomes degraded. Consequently, it is an ideal nozzle for fountains with fish as they generate organic material that tends to decompose water
The jet nozzles with air suction made by Safe-Rain are called ‘Foam Jets’ jet Rain Snow and are produced in two different models, the smaller version made of machined cast brass and the largest made of stainless steel and brass.
Water-drawing and air-suction nozzles
This nozzle is a combination of the two previous models and draws both outside air and water from the basin. It produces a very frothy appearance with greater wind consistency, so that it is able to reach heights well above those obtained with just air-suction nozzles. This nozzle comes in one of two versions – either cylindrical or conical in shape. The diagram in Figure 34 illustrates how the nozzle producing a cylinder-shaped jet works. The illustration shows how the jet impelled through the spout produces a vacuum which, on the one hand, draws water from the basin through the inlet surrounding the pipe and, on the other, sucks in outside air through the upper inlet of the nozzle. The jet produced by this nozzle is cylindrical and the water has a very frothy appearance.
Figure 35 illustrates how the nozzle producing a cone-shaped jet works. The diagram shows the jet of pressurized water impelled through the inner spout produces a vacuum which, on the one hand, draws the water above the nozzle and, on the other, sucks in outside air through the periscope-shaped pipes fitted to the nozzle. The collision between the water jet driven through the spout and the surface of water above the nozzle breaks the sheet of water and draws the water, thereby forming the conical shape of the jet, while the air sucked in through the periscope tubes on the nozzle is what produces the frothiness.