STAINLESS STEEL PNEUMATICS IN WASH DOWN AND CAUSTIC FOOD PROCESSING EQUIPMENT
Choosing the Right Pneumatic Part for the Job
By Michael Nick, Product Sales Manager, Parker Hannifin, Pneumatics Division
Many equipment manufacturers consider pneumatic parts such as valves, air motors, and filters, regulators, and lubricators (FRLs) to be commodity items, focusing their product selection on price and availability rather than on any other characteristics. This nonchalant outlook changes however, when an OEM must decide on components for food processing equipment. Food processing equipment is rugged and hygienic and the internal components must be able to withstand extreme conditions in order to achieve high performance and precision.
The first consideration is always materials.
The caustic spray involved in the wash down cycle in food processing involves hydrogen peroxide and other cleaning agents that eat away at standard aluminum, brass and zinc materials not safely secured in a protective enclosure. Constant exposure to damp and aggressive environments can cause pitting and weaken many metals. If a standard material valve or filter is used in these instances, the upfront cost may be significantly cheaper but there will be zero return on investment. Coatings will peel off, contamination occurs, and poor performance will result.
Stainless steel is therefore the material of choice for these applications and pneumatic parts manufacturers design products with this in mind. Stainless steel is difficult to machine and cast and is definitely more expensive, but in this specialized market, it is a requirement for meeting stringent requirements for hygiene and corrosion resistance.
Most engineers realize they will need a stainless steel pneumatic solution for their processes, but how can they analyze competitive products and determine the right components to fit their needs? There are several factors to consider including performance, NACE and international standards requirements, and external design and ease of maintenance.
Begin the selection process by understanding the details of your corrosive application and the requirements you need to meet, such as pressure, temperature, flow, porting, etc. This sounds obvious, but there are numerous times when a filter or valve is chosen based on cost or size alone and a manufacturer spends hours performing on-going maintenance to remedy the poor selection. Longevity and repeatability are basic requirements for a good pneumatic solution. Choose parts that have been thoroughly tested and designed to withstand the toughest conditions for operation, vibration and impact.
Temperature requirements are another important consideration. In some applications, temperatures go well below freezing. Selecting products, such as an FRL rated to withstand these limits will supply reliability. It is important to remember that temperatures below 32°F (0°C) will cause performance changes because liquid particles become gelatinous or frozen. Air particles must be dry enough to avoid ice formation.
Accessories and options for your pneumatic solutions are other considerations often overlooked during the selection process. Ensure that the entire product is able to withstand the environment. Otherwise you will waste money replacing parts and dealing with inferior performance. For example, typical regulators have a composite adjustment knob or T-handle, which allows outlet pressures to reach their full range. The caustic chemicals used in wash down affects the entire pneumatic product and will corrode anything plastic, so in addition to the stainless steel regulator, make sure the knob is made from similar material.
Look for options on filter-regulators such as a tapped manual drain or an automatic stainless steel drain, which require less maintenance and are typically used in food applications to pipe away excess liquid and avoid draining onto the floor. Non-relieving regulators that do not release gases or liquid into the atmosphere can be critical to clean room environments. If your application allows, select pre-lubed or lubrication-free mechanisms that use food-grade grease and require no added external oil. These are choices you must consider.
Choose the right options.
A global food and healthcare OEM was experiencing aging, problematic signal valves on its machinery resulting in unplanned events during solution injections into 30,000 gallon mouthwash batch tanks. Valves were hard-wired and not connected to the existing serial network causing partial shifts and “hang-ups.” The result was 30,000 gallons of waste product, removal cleanup and production downtime that occurred three to six times per year. Cost avoidance on a bad tank of mouthwash and related downtime was enormous.
The OEM decided to replace the aging valves and install a pre-assembled and thoroughly tested all-in-one manifold solution that met International Organization for Standardization (ISO) requirements. The new valve solution used pressure sensors and serial communications to alert machine operators immediately if a tank was open or closed during batching operations.
Choosing quick connectivity serial communication modules and using sensor feedback to confirm valve shifts completely eliminated the injection failure and the cost of clean up and disposal that resulted (over $37,000 each instance). The OEM saw a return on investment in the first year.
NACE and other international standards
NACE International is an association with 17,000 members in 100 countries with the mission “to protect people, assets, and environment from the effects of corrosion” (www.nace.org). Focused on prevention and control, NACE sets corrosion standards for industries ranging from food processing, oil and gas, and petrochemical to highways, telecommunications, and home appliances. For example, NACE MRO175/ISO 15156 is the international standard for selecting crack-resistant materials for use in corrosive environments. Knowing that your pneumatic components meet NACE requirements is a good guarantee that your equipment will function with the performance you expect.
In addition, there are standards that exist worldwide to define the enclosure type and application. ISO offers standard certification for products in corrosive environments, as well as the National Electrical Manufacturers Association (NEMA) and the International Electrotechnical Commission (IEC) and its associated International Protection (IP) ratings. The NEMA Standards Publication 250 and the IEC publication 529 address the classification of degrees of protection provided by enclosures. More information can be found on their Web sites: www.iso.org, www.nema.org and www.iec.ch.
External design & maintenance
Food processing OEMs should also seriously compare the external design of pneumatic parts for their machines. They must choose a solution that has been designed specifically to meet food processing environments. For example, with air cylinders, a convex shape offers optimum hygiene making the cylinders easy to keep clean. The cylindrical design eliminates air pockets which tend to accumulate dirt or bacterial. A positive external seal between halves of the body obviates possible dirt traps.
It is important to note that although many pneumatic valves meet NEMA standards or IEC/IP ratings, most are mounted in an enclosure to protect them from wash down. Be sure to check the design of this enclosure. The crevices between the valves and sub/manifold bases and other non-smooth surfaces can harbor bacteria. For OEMs that use serial communications with their valves, the electronics also need to be protected from the elements.
Manufacturers should also take note of valves and cylinders that offer pre-lubed or lubrication-free operation. Lubrication-free means that no particles of lubricant will escape with the exhaust air, reducing overall service costs. In order to “set and forget” with any pneumatic component, you need to choose the right product for your application and always perform proper preventative maintenance.
Choose the optimal design
A food processing OEM was fabricating a new line of filling machines for extremely high speed production. It wanted to achieve higher performance with a smaller shop floor footprint.
A redesign of the pneumatic valve system in its machinery using collective wiring and stainless steel FRLs reduced the overall footprint by nearly half and decreased build and installation time. In this case, choosing the right components as well as using a knowledgeable supplier who could understand their overall processes resulted in:
- Reduced control panel size by 50%
- Decreased component prices by $1k versus previous design per machine
- Reduced machine wiring time by 1 hour per machine
- Reduced machine plumbing by 1 hour per machine
- Saved $2,200 per machine (~ 22k per year)
Although choosing an pneumatic component for any industrial machinery often comes down to availability and price, you will save future frustration and ensure optimal performance for equipment that operates in corrosive environments if you examine competitive options. Consider your application and be sure to choose a vendor that can understand your process and has a history of reliability. Inferior parts can be costly to your quality, performance, and maintenance costs.
|Checklist for Pneumatic Components in Food Processing Equipment|
|Pneumatic Component ||Options||Performance Factors||Material||Certification|
|Filters, Regulators, Lubricators (FRLs)||Stainless Steel adjustment knobs, Stainless Steel automatic drains, tapped manual drains, pre-lubed||Watch for temperature, pressure and flow requirements ||316 Stainless Steel to withstand wash down and corrosion|
|NACE, NEMA, IEC/IP Enclosure Standards and ISO|
|Valves||Collective wiring, serial interface, pre-lubed||Ensure all components are protected from wash down, including the manifold, solenoid, and valve body|
|Air Motors, Cylinders||Cylindrical, hygienic design, pre-lubed|
|Perform preventative maintenance per manufacturers instructions to keep optimal performance|
Article courtesy of Parker Hannifin Corporation