All about design of water feature fountains
The solid water jet nozzle was the first cone nozzle to appear in history and at first was the simple pipe-end that we mentioned in the first article of this blog, through which water was discharged at a certain pressure (Fig. 10). Depending on the tilt of the pipe-end, the water jet rises vertically or forms a parabola.
With this type of nozzle, it is very important that the water jet be delivered as crystalline as possible and therefore it is imperative that the water flows in a non-turbulent regime. But considering these jets can reach great heights that require high speed, it is not easy to achieve the desired effect without modifying the inside of the nozzle. In principle, in order to increase speed, the inside of the nozzle narrows (Fig.11). Indeed, as the speed equals the flow rate divided by the pipe section (v = Q/s), the more the section is decreased, the greater the increase in speed will be. Thanks to such increased speed, a higher or greater distance jet can be achieved, but at the same time water turbulence also increases and this impairs the crystalline appearance and jet consistency. To ensure that water returns to a laminar regime, a jet-stop (Fig.12) is fitted that divides the pipe section into several smaller sections to increase the critical speed and ensure the water flow out of each hole in the jet-stop is kept non-turbulent. When these water streams re-join each other, the original jet is achieved but with a laminar regime.Read More
In the old days, such lance jet nozzles were coupled to the pipe with a sleeve made of a ductile material to correct any minor tilting errors. Now, almost all of them are fitted with swivel joints (Fig. 13), otherwise, it is a good idea to fit one between the nozzle and pipe. There are several types of swivel joints, from the simplest that simply aim to correct minor variations in the tilt, to the 360º Rotating Swivel that rotates 360 degrees in one plane and up to 15 degrees in the axis perpendicular to that plane. The latter, given its internal design, is the only one that does not cause turbulence in the jet stream despite being the one that allows for greater tilt angles.
The lance jet is one of the most beautiful and also the most wind-resistant jets, and therefore, most suitable for achieving great heights. Its greatest disadvantage is the large volume of water needed to operate it. To overcome this drawback, the Hollow Nozzle was invented, which differs from the previous one in that the center of the outlet hole is filled with a solid cylinder of smaller diameter than the hole to ensure the water jet has a void in the center (Fig. 14). Externally, the Hollow Nozzle is very similar to the Lance Jet Nozzle and yet water consumption is lower. Consequently, the jet with the central void is less consistent against wind than the lance jet. You have to choose which of the two nozzles is best depending on the height of the jet and typical wind force.
Let us now have a look at Safe Rain lance jet nozzles. Their trade name is the Lance Jet and 21 different sizes are produced to achieve a range of jet heights up to 140 meters. They are all equipped with Jet-Stops and Swivel Joints. The smallest nozzles, which can produce jets of up to 14 meters high with diameters of between 4 and 19 mm, are very carefully designed to look similar to the original nozzles (Fig. 15). But, instead of having a hexagonal nut and stud (like other brands on the market), Safe-Rain nozzles are cylindrical and have a knurled nut to make them easier to tighten. This way, they are more elegant and do not look like an industrial item as occurs with the hexagonal shape. The jet-stop is designed so that the swivel joint rests on the jet-stop (Fig. 16) instead of holding the stud. Thanks to this design, the swivel rotates very smoothly compared to the abruptness seen with other brands. Similarly, several of the models come with two jet-stops, as discussed below, to produce a more crystalline jet, even with very high jets.
**Installation Tips: As indicated above, it is of utmost importance that the water be in laminar regime for it to have a crystal clear appearance and for the jet to reach greater heights. To achieve this, the nozzle is fitted with a jet-stop or even two jet-stops in certain models. But it also has a swivel joint which, depending on its tilt, can produce the opposite effect. In general, it is best not to swivel the joint more than between 5 and 10 degrees (depending on the height of the jet), but this does not exclude the possibility of producing water jets with greater tilt, provided they are properly installed.
Laminar Jet: A very special type of lance jet is called the Crystal Jet (or Rainbow when accompanied by colored lighting), which is different from the other jets in that the jets have a fully laminar regime (Poiseuille regime) and is capable of such perfection that it produces a jet that looks like a rod of solid glass rather than running water. It is so perfect that each drop of water traces an independent path from the others and so if each one is lit up, it works like a strand of optic fiber and transmits light along the entire length to the end of the water jet . Due to the difficulty of achieving a Poiseuille regime directly in the installation, the Crystal Jet Nozzle is sold as a stand-alone, ready to install unit that just needs a water and electricity connection.
In the next post on this blog, we will continue talking about water-drawing and air-suction nozzles, both of which are widely used in the design and installation of architectural fountains.