In a sanitary application, a rotary valve’s design and construction materials must meet hygienic standards to ensure that the product reaches the customer without contamination. Product recalls due to contamination can be costly to the manufacturer’s bottom line and reputation. Therefore, it essential to evaluate and categorize the contamination risks in handling the conveyed product. At a minimum, your rotary valves and other material handling equipment must comply with the regulatory hygiene requirements in the country where your product is manufactured
Well-known independent organizations have developed standards for designing equipment for hygienic applications: The United States Department of Agriculture (USDA) and European Hygienic Engineering & Design Group (EHEDG). Their standards are accepted around the world. The following information covers the minimum, mid-level, high-level, and highest-level hygiene requirements for rotary valves handling products in sanitary applications.
Minimum hygiene requirement
In general, the minimum hygiene requirement for a rotary valve in a sanitary application is that all the valve’s product-contact surfaces be made of FDA-approved materials. These include AISI 304 and AISI 316 grades of stainless steel, which have relatively low cost, are durable, resist corrosion, and FDA-approved plastics, polymers, and rubbers. The minimum hygiene requirement permits aluminum or mild steel construction for nonproduct-contact surfaces. Aluminum or mild steel surfaces are usually plated, painted, or powder-coated to protect them from corrosion.
The rotary valve commonly used to meet the minimum hygiene requirement in sanitary applications is a valve with a fixed-vane, chamfered (beveled-edge) rotor. The minimum hygiene requirement for this type of valve typically allows the inlet and outlet to be left as cast (without further finishing). Generally, it requires surface finishes for the valve’s machined product-contact parts to be around 3.2 Ra.
For applications requiring regular valve cleaning, select a valve with an easily detachable rotor to facilitate dry cleaning. To clean the valve, remove the end cover opposite the valve’s drive, remove and clean the rotor, and then use a vacuum cleaner to remove the product from the valve interior and shaft-sealing assembly. (You should not use a compressed-air hose to clean the valve because it can spread product and contaminate the surrounding area.) Use wet sanitary wipes to remove any remaining product, and then dry the valve before reassembling it and putting it back into use.
Mid-level hygiene requirement
Dry cleaning. The rotary valve must have a fixed-vane rotor with a radius machined between the vanes, and the blades should be chamfered on three sides. All valve’s product-contact parts, including the inlet and outlet, must be machined or polished to 0.8 Ra (180 grit) and be free of pinholes and crevices. To facilitate cleaning, the valve interior should have no sharp corners. Instead, all corners should have a radius of at least 0.8 millimeters.
When the valve requires cleaning, you must first remove the drive-side end cover and remove the rotor (called out-of-place cleaning or COP). After this, the dry-cleaning procedure is the same as that for the minimum hygiene requirement. You can simplify the cleaning procedure by choosing a valve with slide rails or bars mounted on its exterior. The rail design supports the non-drive side end cover and allows you to easily remove the rotor and end cover without damaging the housing or rotor blades. The stability of the extraction mechanism ensures accurate alignment and tight clearances. Moreover, the rail support system increases operator safety and gives line operators considerable flexibility in cleaning the equipment between runs. On a large valve, slide rails are especially important because the components withdrawn from the valve will be heavier.
Wet cleaning. Discharging a powder produced from a wet mix in a spray dryer is a typical sanitary application for a rotary valve that must meet the mid-level hygiene requirement and require wet cleaning. To select a rotary valve for this hygiene level, start by following the same mid-level hygiene guidelines for a valve that requires dry cleaning, including using the same construction materials and finishes.
To ensure that the valve can withstand wet cleaning, follow these additional guidelines: Make sure that any cracks, crevices, and other areas on the valve exterior where the product may accumulate are sealed with an FDA-approved silicone or epoxy sealant. Prevent rust or flaking of the coatings by using stainless steel guards and fittings wherever possible. Choose a valve with bearings that are protected from cleaning liquids. Ensure that the valve’s drive-side end cover is fitted with an O ring or gasket so that if the valve is cleaned without removing the drive-side cover, no product or cleaning liquid can enter between the metal cover and housing surfaces and cause contamination
In some applications, a valve may require more frequent cleaning than a mid-level-hygiene valve. Whether your valve requires a COP or CIP (cleaning in place) procedure will depend on your product and process. A typical COP wet-cleaning cycle includes removing the non-drive-side end cover and rotor, placing a dummy shaft between the end covers, and closing the valve. The rotor should then be cleaned out of place. Next, rinse the valve several times with a series of liquids, in this order: warm water, a caustic liquid, warm water, a liquid with a low acid concentration, a very large amount of water, a disinfectant, and, finally, clean water with low bacteriological contamination (often tap water, sometimes with an added sanitizer). Remove the non-drive-side end cover and dummy shaft, clean both shaft sealing areas, and then replace the cleaned rotor and reassemble the end cover. After these steps, dry the valve with hot air.
High-level hygiene requirement (wet cleaning)
High-level hygiene applications can require an intensive wet-cleaning process. This often includes the use of acidic, alkaline, or caustic chemical cleaning solutions and sanitizers and manual scrubbing of the valve components. The valve’s cleaning frequency depends on your product and process.
When selecting a high-level-hygiene rotary valve, you can follow the same guidelines listed for the mid-level-hygiene valve. Also ensure that the rotary valve’s wet-cleaning requirement is accepted by an independent third-party organization (such as the USDA or EHEDG) that inspects and validates valve component designs according to specific criteria.
Highest-level hygiene requirement (CIP wet cleaning)
The wet-cleaning CIP procedure requires a CIP-equipped rotary valve that does not require disassembly for cleaning. Cleaning is automatically controlled without operator involvement. The typical CIP cleaning procedure would include the same liquids and drying process as for CIP cleaning elsewhere in the plant.
A rotary valve that must meet the highest-level hygiene requirement can be equipped for automatic CIP wet cleaning and can also be fitted with a complete stainless-steel-geared direct drive. Such a valve’s end covers will have o-rings or gaskets, and the valve should have shaft seals equipped for CIP. This valve can handle the same applications listed for the high-level hygiene requirement but operates in a fully automated conveying system. It allows wet cleaning without a need to open and disassemble the valve for cleaning and without requiring an operator’s involvement. This not only eliminates cleaning labor costs and the risk of damaging the valve but also prevents bacteria and other contaminants from entering it. The automated CIP method is more reliable than manual wet cleaning and can be validated to demonstrate that the valve is properly cleaned according to your hygiene requirement. Ensure that you select a CIP rotary valve certified by a third-party organization to confirm that it has been tested and validated by that organization.