What is a nozzle or distributor?
A nozzle or distributor is an element that prevents a filtering or purifying granular media from leaving the tank or vessel.
The structure of a nozzle or slotted element allows to place more filter media than in a conventional slotted or perforated tube and to place several layers of gravel.
In this article we are going to see how a slotted Johnson nozzle works in a water filter.
What are the nozzles or distributors of a filter?
It could be called “filter” because it merges like a mesh, which its main purpose is not to filter, but to retain a granular filter media or purifying agents inside the container that contains it, typically can be manufactured in stainless steel, PVC plastic, ABS or Kynar.
The nozzle has a mesh or slotted element with a very particular shape, it consists of very resistant profiles that are usually V-shaped and mounted on different support profiles.
Normally, this V-shaped wire is rolled over these profiles in a circular shape and with a millimetric separation between one and another, this assembly forms a continuous groove that we can call the filtration zone or slotted element.
The V-shaped surface profile usually forms conical grooves that help; if a grain gets stuck between one groove and another, with a little pressure it is easily untied, which avoids a general clogging of the entire nozzle.
Therefore, in its construction it is essential to control this distance between groove and groove very precisely.
Advantages and disadvantages of nozzles or distributors
If you are wondering in which applications can I use the nozzles and if we have any advantage, here are the advantages that you will obtain when using the nozzle.
First of all, there is no clogging or plugging as in other conventional screens or filters. Remember that the filter element forms an uninterrupted slot that allows a very fine two-point spacing, thus minimizing the effect of clogging by grains. Non-clogging provides effective peak flow and efficient operations. It also reduces cleaning downtime and related cost as a result of filter plugging.
Also the V-shaped wire has an additional, allows for easy cleaning or backwashing of the filter media.
Cylindrical shape to withstand high pressures
The manufacture of Johnson type nozzles by welding a circular shape to a support, avoids the need for cups because the cylindrical elements are more resistant to high pressures.
High precision slot spacing
Nozzles or hydrospheres come in different slot sizes, allowing you to select one suitable for your application. Filters can have slot openings ranging from 0.025 mm to 12.5 mm, depending on the particle size.
The fabrication of a Johnson type slotted element is done on cross rods that are the support for the “V” shaped wire that is then wound. This assembly is made with a machine that has a millimetric precision, which is welding at the points of coincidence with the support rods.
The welding provides additional resistance to the nozzle. This resistance is vital to withstand the operating pressures.
Good distribution of the liquid being treated
An advantage of using nozzles or distributors is that it generates an even distribution of the liquid inside the filter. This ensures that the filter media is not concentrated on one side or in the center of the tank, and that the bed remains as horizontal as possible.
The rule for a good arrangement and distribution of the nozzles is as follows:
Placement distance between centers of 2 nozzles: Optimum 6 inches and maximum 12 inches between each one.
Nozzles have various designs due to manufacturer variations, so multiple shapes can be manufactured, some are conical in shape, the most typical are cylindrical, spherical (hydrosphere) or flat.
How to select the type of nozzle we need?
Nozzle filter sections
In this chapter we will see the main sections of a nozzle.
1. Surface profile of a nozzle
The surface profile of a nozzle is composed of a V-shaped wire. But, there are four types of surface or wire types available for a nozzle, i.e., flat wire, triangular wire, round wire and trapezoidal wire.
The main material for the manufacture of most nozzles is stainless steel, due to its characteristics of stability of this material to be in contact with drinking water, its support at different temperatures and pressures, as well as avoiding rust.
The size of the slot opening (space between wire and wire) available for the surface profile varies from 0.8 mm to 3.4 mm. The most common opening is 0.18 mm.
2. Nipple of a nozzle
The nipple that is welded to a nozzle, performs the support and allows connection to a central distributor pipe, typically 3/4″ and 1″ (inches) in NPT or straight millimeter type.
The nipple should be of the same material as the filter element, either Johnson type or plastic.
3. Johnson type slotted tubes
The slotted tubes are used to manufacture the nozzle, which is composed of a fraction of a slotted tube, two torsospherical caps and a nipple, all made of the same material as the filter element.
As we have seen, the slots have the same separation size. In some nozzles, you can have variable slot openings for special purposes. The ability to combine different components in a nozzle indicates that there is no standard pipe or slot size on the market.
4. Service Flow
The flow rate of a nozzle is the direction and the liters or gallons that pass through it in a given time during the filtration process. A nozzle basically has two flows, i.e., inlet to outlet flow (service flow) and outlet to inlet flow (backwash). As we will see later in this guide, certain factors determine the directional flow of a nozzle.
Direction of flow in nozzles
Service flow (inlet to outlet)
The inlet to outlet flow, also known as service flow, is the start-up of the filtering equipment where the nozzle captures the already filtered or treated water.
This flow can be determined depending on which nozzle is to be used and with which pipe diameter or nozzle nipple, we will be glad to help you choose the right nozzle to calculate the number of nozzles you need to place.
Backwash Flow (Outlet to Inlet)
Outlet to inlet flow, also known as backwash flow, occurs when the filter enters backwash or cleaning mode and reverses flows in reverse. Water enters the outlet to lift the media bed to expand, loosen and clean it of retained sediment.
The construction of the nozzles is quite easy. Basically, nozzle construction consists of wrapping a cylindrical profile wire around a longitudinal support rod and welding the wire and rods at each contact point with robotic machinery for precise welding at the correct distance.
External circumferential standard
The external circumferential standard occurs when the direction of fluid flow is on the outside to the inside. Remember, vertical rod support is crucial in such a construction.
Inner circumferential winding
In inner circumferential winding, the fluid flow is from the inside to the outside, for which the outer rod support of a nozzle, which is horizontal, is used.
External winding uses the vertical rod to allow the flow of the fluid, which in this case flows from the inside to the outside.
A typical nozzle uses slotted elements with internal winding.
What to look for when buying a nozzle?
If you want the best for your filtration, you need to select the best water distribution in a pool, false bottom or closed tank type filter by paying attention to specific details.
What specification must a nozzle meet?
The big question is what are these specifications that you must meet. To answer this, here are the specifications you should check when you go to buy a nozzle.
Understand the nature and size of the particles in a granular media bed to select a nozzle. The particle size of the media should be twice the size of the nozzle slot. To make sure that the filter media will not leak out of the nozzle slots.
Maximum operating flow rate
The flow rate will determine the size of the filter to be used. In other words, the number of nozzles must be adjusted to the flow rate of the fluid. Most nozzles have on their data sheet an indication of the maximum flow rate they can handle. Check the corresponding flow indication to select the correct nozzle.
Maximum and minimum operating pressure
Each filter has a maximum operating pressure it can withstand. Therefore, it is necessary to select a nozzle that matches the operating pressure of your application. The greatest care is taken with plastic nozzles or manifolds, as these can collapse at lower pressures than stainless steel ones.
This is to avoid a collapse of the nozzle or manifold during operation, which can lead to poor fluid leakage. Understanding the minimum operating pressure is essential when dealing with a self-cleaning nozzle. When the backwash mechanism is activated, it is necessary to maintain the minimum operating pressure.
Each nozzle in its specification will mention its maximum operating pressure.
Pressure drop is the decrease in fluid pressure across the filter. A first pressure drop is in the filter control valves (in the data sheet you can see how much pressure drop can be generated by the valve used). As the pressure forces the fluid through a filter media where filtration or treatment takes place, a second pressure drop is generated.
As a result, there will be a resistance to the flow of the fluid which results in a pressure drop once the fluid flows through the filter.
There are several factors such as contaminants, viscosity and flow rate that cause the pressure drop.
Pressure drop is an essential factor because when the filter starts to become dirty, the pressure drop increases, resulting in a decrease in flow and contaminants filtered out.
Nozzles should not have a pressure drop, as they should be designed to neither stop nor decrease the service flow.
When the pressure to be overcome is too great, the desired flow through the filter is compromised, so it is necessary to remove contaminants to reduce the pressure drop frequently. Therefore, when selecting a nozzle, the pressure drop must be taken into account, as it will influence the frequency of cleaning.
Cost is certainly an important factor when choosing a nozzle, as you need to keep operating and maintenance costs low.
One way to keep operating cost low is to make sure that you select a quality nozzle, as you can’t be opening filters for media or nozzle changes on a frequent basis. That’s why you can approach one of our engineers to help you make the right choice.
Risk of environmental exposure
Finally, you must consider the environment in which a nozzle will operate, in terms of temperature, chemicals and physical environment.
ABS or Kynar nozzles and hydrospheres are the most likely to withstand chemicals or high corrosion. But not very high pressures.
Stainless steel nozzles are more durable and can be exposed to higher pressures, but are not a viable option for high salinity or acids.
Our nozzles have a wide range of applications, such as in the food industry, beverage industry, fertilizer industry and seawater treatment plants.
It turns out that nozzles play a crucial role as a component of a filter. The advantages of these distributors are enormous when compared to other systems. However, it is necessary to consider several factors before selecting a nozzle suitable for your application. Failure to do so can result in a poor choice and cause pressure drops if it is not the correct slot, connection diameter, sufficient number of nozzles to supply the flow, or unsuitable material for the characteristics of the liquid. You can make your work easier by purchasing nozzles from a reliable manufacturer.
We guarantee the quality and durability of the nozzles for your application.