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Spray system optimization eases maintenance crunch
By Jon Barber
Spraying Systems Co.
If you could reduce maintenance time for a critical system at your facility by 50 percent or more, would you be interested?
And if you could document the financial savings for that reduction, would that be valuable to your department?
Thanks to recent developments in spray nozzle technology, you may be able to do both.
Spray nozzles are vital components in many production facilities. Their accuracy and durability are absolutely essential to maximum uptime.
A spray system that is not working optimally can drain staggering amounts of money from your operations. The cost of wasted water alone can approach $100,000 annually even in a system with relatively minor performance problems.
Factor in all the related expenses – the cost of excess chemicals, wasted energy, extra scrap caused by quality problems, unscheduled production downtime, and additional labor – and the true total can quickly mount to hundreds of thousands of dollars per year. That’s serious money. Fortunately, a fast and convenient calculator is now available online at www.spray.com/save to help you figure out the actual costs of sub-par spray nozzle performance in your own application.
Once you appreciate the magnitude of the issue, you’re ready to begin the process of optimizing your spray system. Start by acquainting yourself with the typical sources of spray problems.
Causes of spray nozzle troubles
They may look simple enough, but spray nozzles are highly engineered precision components that can wear over time or suffer damage during normal operations or even cleaning. These are the most common problems that cause substandard spray performance:
Erosion/wear: Gradual removal of metal causes the spray nozzle orifice and internal flow passages to enlarge and/or become distorted. As a result, flow usually increases, pressure may decrease, the spray pattern becomes irregular and liquid drops become larger.
Corrosion: Spray nozzle material can break down due to the chemical properties of the sprayed material or the environment. The effect is similar to that caused by erosion and wear, with possible additional damage to the outside surfaces of the spray nozzle.
High temperature: Certain liquids must be sprayed at elevated temperatures or in high-temperature environments. The spray nozzle may soften and break down unless special temperature-resistant materials are used.
Caking/bearding: Buildup of material on the inside, on the outer edges or near the orifice is caused by liquid evaporation. A layer of dried solids remains and obstructs the orifice or internal flow passages.
Clogging: Unwanted solid particles can block the inside of the orifice. Flow is restricted and spray pattern uniformity disturbed.
Improper re-assembly: Some spray nozzles require careful re-assembly after cleaning to ensure that internal components, such as gaskets, O-rings and valves, are properly aligned. Improper re-assembly causes leaking and inefficient spray performance.
Accidental damage: Damage to a nozzle orifice can occur if a spray nozzle is dropped or scratched during installation, operation or cleaning.
Detecting worn spray nozzles
This task is tougher than it sounds.
The human eye is a remarkable instrument, but it simply can’t give you the true story when it comes to actual spray nozzle wear.
Good spray tip
Worn spray tip
The graphic illustrates this problem dramatically. The spray tip on the left is new, and sprays properly. The spray tip on the right is worn, and sprays 30 percent over capacity. The difference is totally undetectable with the naked eye – but there are other tip-offs that something is amiss.
Watch for these clues:
Quality control issues and increased scrap. Worn, clogged and damaged spray nozzles will not perform per specification, and can result in uneven coating, cooling, cleaning, humidifying and drying.
Increased maintenance time. Unscheduled spray system downtime, or an increase in cleaning frequency, is an indicator of spray nozzle wear.
Flow rate change. The flow rate of a spray nozzle will increase as the surfaces of the orifice and/or the internal core begin to deteriorate. In applications using positive displacement pumps, the spraying pressure will decrease as the spray nozzle orifice enlarges. Even small changes in flow rate can have a negative impact on quality, so routine monitoring can reveal potential problems. But in some instances, the spray pattern will look fine – so it will be necessary to actually collect and measure the spray fluid output in order to reveal wear.
Deterioration of spray pattern quality. When orifice wear occurs in hollow cone spray nozzles, spray pattern uniformity is destroyed. Streaks develop and the pattern becomes heavy or light in the circular ring of fluid. In full cone spray nozzles, the pattern distribution typically deteriorates as more liquid flows into the center of the pattern. In flat fan sprays, streaks and heavier flows will be visible in the center of the pattern and the effective spray angle coverage will decrease.
Spray drop size increase. Liquid flow will increase, or spraying pressure will decrease, as nozzles wear. The result? Larger drops and less total liquid surface area. This is tough to detect visually, so if you suspect a problem, arrange for drop size testing.
Lowered spray impact. Worn spray nozzles operate at lower pressure, generally resulting in lower spray impact. (Ironically, in applications with centrifugal-type pumps, impact may actually increase because of increased flow through the spray nozzle.) Special testing may be required.
Preventing and solving spray nozzle problems
A comprehensive spray nozzle maintenance program will help ensure fewer headaches at your facility. By setting a regular schedule, you can address key issues before they cripple your production line.
The checklist that follows should become the foundation of your maintenance program. Consistent evaluation of these factors will enable you to detect wear early and take appropriate action. Your own particular application will determine how often each factor should be checked. The proper frequency could range from “the end of every shift” to “every few months.”
By implementing a nozzle maintenance program and documenting your procedures, you can determine the best nozzle maintenance and replacement strategy for achieving optimal performance.
Be sure to check these factors carefully:
For centrifugal pumps: Monitor flow meter readings to detect increases. Or, collect and measure the flow from the spray nozzle for a given period of time at a specific pressure. Compare these readings to the flow rates listed in the manufacturer’s catalog or compare them to flow rate readings from new, unused spray nozzles.
For positive displacement pumps: Monitor the liquid line pressure for decreases; the flow rate will remain constant.
Spray pressure (in nozzle manifold)
For centrifugal pumps: Monitor for increases in liquid volume sprayed. The spraying pressure is likely to remain the same.
For positive displacement pumps: Monitor pressure gauge for decreases in pressure and reduction in impact on sprayed surfaces. The liquid volume sprayed is likely to remain the same. Also, monitor for increases in pressure due to clogged spray nozzles.
Visually inspect the spray pattern for changes. Check the spray angle with a protractor. Measure the width of the spray pattern on the sprayed surface. If the spray nozzle orifice is wearing gradually, you may not detect changes until there is a significant increase in flow rate. If uniform spray coverage is critical in your application, request special testing from your spray nozzle manufacturer.
A Patternator measures spray distribution.
The data is used to determine the optimal spray
nozzle height and overlap in an application.
Drop size increases cannot be visually detected in most applications. An increase in flow rate or decrease in spraying pressure will affect drop size.
Check uniformity of spray coverage of flat spray nozzles on a manifold. Spray patterns should be parallel to each other. Spray tips should be rotated 5 to 10 degrees from the manifold centerline.
Product quality/application results
Check for uneven coating, cooling, drying, cleaning and changes in temperature, dust content and humidity.
Four ways to extend spray nozzle life
There are some techniques you can employ to prolong the useful life of your spray nozzles. Consider the following:
Improve cleaning procedures. Remember, nozzles are precision instruments. Cleaning should be done regularly but very carefully, with materials that are much softer than the nozzle orifice surface. Use plastic bristle brushes, wooden probes or plastic probes. Never use wire brushes, pocket knives or welder’s tip cleaning rasps. It is very easy to damage the critical orifice shape (or size) and end up with distorted spray patterns or excess flow. If you are faced with a stubborn clogging problem, try soaking the orifice in a non-corrosive cleaning chemical to soften or dissolve the clogging substance.
Add line strainers, or change to spray nozzles with built-in strainers. Orifice deterioration and clogging is typically caused by solid dirt particles in the sprayed liquid and is particularly common in systems using continuous spray water re-circulation. Strainers, or spray nozzles with built-in strainers, are recommended – with a screen mesh size chosen to trap larger particles and prevent debris from entering the spray nozzle orifice or vane.
Decrease spraying pressure. Although it is not always possible to implement, decreasing the pressure – which will slow the liquid velocity through the orifice – may help reduce the wear and corrosion rate.
Reduce the quantity of abrasive particles or concentration of corrosive chemicals. In some applications, it is possible to reduce the amount of abrasive particles in the feed liquid, and/or change the size and shape of the particles to reduce wear effects. Also, the corrosive activity of a solution can occasionally be reduced by using different concentrations or temperatures, depending on the specific chemicals involved.
The pros and cons of replacing nozzles more frequently
If, after implementing a spray nozzle maintenance program, you determine that your current nozzles aren’t performing as well as they should, you’ll need to evaluate if it costs more to keep using problem nozzles or to replace them. Consider the following factors:
The cost and length of production downtime due to nozzle problems and maintenance
The cost of labor for the additional maintenance
The cost of spraying excess water and chemicals
The cost of increased energy usage
The cost of quality problems — increased scrap and/or process problems
In some applications, it may be possible to compensate temporarily for a worn orifice by decreasing the spray nozzle pressure to deliver the original required flow rate. However, using lower pressures may compromise spray coverage and uniformity of the spray. Larger drop sizes and lower impact may result. In the end, using lower pressures may be a false economy since you could experience quality problems.
If your replacement intervals seem too short, you may be better off changing to a different nozzle. The additional short-term cost is usually quickly recouped through longer wear life and better performance.
Durability and resistance issues
It’s also important to keep in mind that replacing your old spray nozzles with nozzles made of the same material (for example, replacing an aluminum nozzle with an aluminum nozzle) may not be the best way to go. Obviously a new spray nozzle is superior to a worn nozzle, but your situation may call for replacing current spray nozzles with nozzles that are much better suited to handle the types of liquids and chemicals that you routinely use.
Spray nozzles made of harder materials generally provide longer wear life. Predictably, stainless steel has a greater abrasion resistance ratio than aluminum, while carbides provide far greater abrasion resistance than stainless steel. To determine whether you should consider a different material for nozzles, spray tips or orifice inserts, consult the chart below.
Abrasion resistance ratio chart
In addition to abrasion resistance, you may need to consider the corrosion resistance of your nozzle material. The rate of chemical corrosion on a spray nozzle depends on several factors, including the corrosive properties of the liquid being sprayed, its concentration in the solution, its temperature, and the properties of the nozzle material. A leading spray nozzle company can analyze these factors and offer an appropriate recommendation.
A reliable spray nozzle manufacturer should be able to offer you high-quality nozzles in a variety of materials – and to design custom nozzles for you when the situation calls for unique or specialized applications.
Quick-maintenance nozzle types
Fortunately, many nozzles can be installed and replaced without the use of any tools. This makes the whole process faster, easier and more reliable than ever.
New types of spray nozzles feature extremely convenient, non-slip extensions that are easy to grip and twist even in wet or sticky conditions involving lubricants, oils or other viscous materials – and even if the maintenance person is wearing gloves. Also, look for single and double pipe clamps that enable you to quickly change entire nozzle mounts whenever necessary.
Look for nozzles with features that reduce installation and maintenance time.
Get expert assistance
A reputable spray nozzle manufacturer doesn’t just sell you hardware. A top company should partner with you by offering nozzle maintenance workshops, featuring on-site inspections and professional training for your staff.
In addition, your manufacturer should have the capacity to test and evaluate spray nozzles with state-of-the art equipment to help establish baseline performance measures that will guide your cleaning, maintenance and repair schedules. This can minimize downtime significantly, and help avoid quality control issues through timely spray nozzle replacement.
The fact is that major savings in time and money can be achieved through an aggressive Spray System Optimization Program. The impressive results can be proven – and they will demonstrate the vital importance of your department to overall company efficiency.
About the author:
Jon Barber is a director at Spraying Systems Company in Wheaton , Ill. He can be reached via e-mail at firstname.lastname@example.org. For a free copy of the Spray System Optimization Handbook, call 1-800-95-SPRAY.