Nozzle Maintenance Strategy
Have you ever tried to wash your car or water your lawn with a malfunctioning nozzle that is spurting water from the hose and/or handle connection? It’s a frustrating endeavor, no doubt. But before a nozzle gets to the point that it is actually losing water at its joints, chances are it has gone through a long and arduous process of degradation. Quite possibly, the nozzle orifice has been collecting sediment and its performance has deteriorated due to improper maintenance. Or the leaking could be the product of other issues, ranging from spray pressure to flowrate to capacity to spray angle to nozzle wear to material compatibility issues and so on. Whatever the case, the end result is the same: you, standing cold and wet in front of the azalea bushes in your back yard.
Now, consider this scenario (sans azaleas) in an industrial spray application. In such an environment, the cost of an improperly functioning nozzle can run into the thousands or even tens of thousands of dollars per year. Take it a step farther, and consider a precision spray application where the process fluid is more expensive.
To help users combat such problems, spray technology manufacturer Bex Engineering LTD (www.bex.com) has compiled a series of maintenance tips for nozzle users. The list covers:
• Worn Nozzles
Prevention:
– Ensure the nozzle material is compatible with the fluid temperature.
– Reduce spraying pressure to reduce the liquid velocity.
– Minimize the abrasive particle content.
– Consider a different type of nozzle material.
• Damaged Orifices
Prevention:
– Use a fiber brush to clean the nozzle (avoid using metallic objects).
– Remove the nozzle from the connection to clean it.
– Soak overnight to remove caked residue.
• Excessive Leaking
Prevention:
– Verify connections between the nozzle and pipe fitting or manifold.
– Ensure proper sizing.
– Check for worn o-rings.
• Improper Alignment/Aim
Prevention:
– Document nozzle orientation prior to removal for cleaning.
– Verify nozzle aim when reconnecting to the pipe or hose.
– Consider a quick-connect/disconnect nozzle with features for auto-alignment.
Though not as impressive in physical stature as the big iron workhorses common to industrial fluid handling environments, or as complicated as some of the devices found in precision fluid applications, the importance of spray nozzles to overall process efficiency should not be underestimated. The nozzle is often the last piece of equipment that governs a fluid in a given application, and, if neglected, the nozzle may be the downfall of a fluid handling system.
According to William J. Kohley, Ph.D., vice president of AutoJet Technologies (www.autojet.com), the precision spray control division of Spraying Systems Co. (www.spray.com), an improperly installed, worn, or damaged nozzle may deliver up to 20 percent more flow than intended before a problem becomes recognizable to the human eye. As a result, he says end-users that do not pay special attention to their nozzles may be unconsciously generating a tremendous amount of waste in their process. "If you’re spraying 20 percent more than you need to be, and you can’t see it, you are blind to the inefficiencies of your process," says Kohley.
Application Pitfalls
Kohley says the primary pitfall in applications that involve spray technology is assuming that "if it sprays, it must be OK." He says this is a risky assumption, as poorly maintained nozzles may not only result in excess flow, but also greater than 35 percent spray pattern variation. "Uneven distributions result in uneven coatings and uneven process results," says Kohley. "Again, this is difficult for plant personnel to detect visually."
Another common pitfall Kohley cites is the perception among end-users that "if a little is good, more must be better." By nature, Kohley says the first instinct many users have when the spray system isn’t working is to turn up the volume. "More isn’t better in today’s process plants where advanced chemistries are often concentrated and effective in smaller dosages than they were 10 years ago," he says. Further, the "more is better" approach isn’t consistent with today’s industrial plants where environmental and worker safety concerns are scrutinized and regulated more than ever. "Excess volume is a detriment to compliance programs," says Kohley.
In an effort to help end-users more effectively leverage spray technology for process efficiency, manufacturers are developing new automated spray nozzle technologies that provide a wide range of flow control solutions within a single nozzle tip. New technologies offer turndown ratios as great as 100-to-1, with no deterioration of pattern uniformity, droplet size, or spray distribution.
Technological Solutions
Among the key technological advances that have enabled users to improve the efficiency of their spray applications is in the area of computational fluid dynamics (CFD). CFD software enables nozzle manufacturers and end-users to model and test spray technology to optimize it for specific applications. Whereas cutting-edge technology 15 years ago involved intensive research into particle sizing, coating uniformity, and fluid physics — specifically the behavior of droplets and spray patterns in turbulent environments — this application information can be replicated and modeled through CFD. As such, Kohley says "[modeling] has gone from the research community to the process and application community."
Kohley says application-specific modeling allows, for example, more precise placement of nozzle lances in scrubber towers to improve the overall heat transfer of the tower. In precision applications, Kohley says advancements in industry software and hardware platforms have helped improve sensor and meter resolutions. For example, he says a clean, filtered process signal with incrementally better resolution over greater bandwidths has allowed improved tuning of spray nozzle characteristics in closed-loop systems. Nozzle sensing technology for determining clogs, pressure differentials, and pattern alignment has also emerged as a useful tool for resource conservation, according to Kohley.
Best Practices
In order to maximize spray efficiency, Kohley recommends end-users "start with the end in mind." He says, "At the end of the day, you want to spray the minimum amount to get the maximum product quality." Thus, he says end-users should measure end-product quality first and distinguish the qualitative and quantitative impact the spray application has on product quality. "Users have a tendency to look at the control and pump system first, then work their way to the spray nozzle," says Kohley. In reality though, he says understanding the direct link between end-product quality, chemistry, and spray performance is the best approach to initiating a reliable production spray system process.
Regarding spray pattern and nozzle tip selection, Kohley says testing is key. Rather than practicing trial and error on the production line, Spraying Systems recommends thoroughly analyzing the end-product composition, geometry, and production process variables in a test environment. Kohley says it is equally important to test around the chemistry (i.e., viscosity, specific gravity, percent solids, and process characteristics). "Only then can we narrow down a range of nozzles and spray control parameters that best position a test for success," says Kohley. Once success has been achieved in a test environment, the end-user can scale the solution up to support a live production environment without having to experience significant waste in the process. "Doing trial and error on production lines can solve the immediate spray challenge, but often leads to time consuming and expensive changes when new production or process variables are introduced," says Kohley.
While Kohley acknowledges the nozzle is probably pretty low on the priority list of plant personnel in today’s chaotic manufacturing environments, he says that when he meets with plant managers, they are generally receptive to the idea of optimizing their spray technology because they see the opportunity for significant cost savings. "I’ve never run into a situation where there was a spray application that we couldn’t help in at least some small way," says Kohley.
Often, Kohley says chemical companies will refer Spraying Systems to their customers after receiving repeated complaints about the amount of chemical being used in a given application. And while they may do it begrudgingly, Kohley says the chemical companies refer their customers to Spraying Systems because they know spray optimization can help improve the efficiency of the chemical process.
The Future
Going forward, Kohley says end-users should look for advances in precision spray nozzles, spray control technology, and spray modeling research and simulation. For example, he says a new range of anti-bearding nozzle assemblies allows pharmaceutical manufacturers to produce more product with less downtime for cleaning spray manifolds. In addition, he says new spray control products take advantage of improved temperature and humidity sensor resolutions, enabling tight monitoring and control of the quality and moisture content of consumer products, such as tissue paper and roofing shingles. Kohley also sees continued proliferation of spray technology, as universities and leading industry spray experts cooperate to model new flow characteristics of droplet behaviors for new products, such as injection systems, drug inhalers, and high-effic. process towers.
Matt Migliore is the editor of Flow Control magazine. He can be reached at [email protected].
