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Improving the Hygienic Design of Valves
Chapter 23
Improving the Hygienic Design of Valves F. Tracy Schonrock Schonrock Consulting, Fairfax Station, VA, United States
23.1 INTRODUCTION Sanitary valves are ubiquitous throughout processing systems. Without them, modern processing systems would be cumbersome and inefficient. Valves provide operators with the ability to stop, direct, meter, and control the flow of products and ingredients throughout the process. Because of their widespread use, valve design and sanitation can impact on every particle of product passing through the process system.
23.2 VALVE TYPES Valves come in multiple configurations. They are well developed to operate in systems that process fluids, semifluids, fluids with particulates, viscous products, and dry products. Some valve designs operate well in more than one of these different environments.
23.2.1 Valves Commonly Used in Fluid Product Processing Systems The following are descriptions of valves commonly used in processing systems for fluid products, including viscous products and products with semisolid or solid particulates within the product stream. ●
●
●
●
●
●
Plug valve (Fig. 23.1): a simple design consisting of a tapered plug inserted into a tapered body. The valve can be configured as a shut-off valve or with one or more ports to direct flow to different product streams. The valves are most commonly manually operated but can be affixed with a power actuator. Plug valves are not generally used in dry product applications. This design is not suitable for clean-in-place (CIP) techniques and requires complete disassembly for manual cleaning. Leak protection valve: a leak protection valve is a specialized plug-type tank outlet valve that is used on vat pasteurization equipment. The design includes special features that will prevent leakage past the valve by controlling how far the valve may be turned and the inclusion of grooves to provide leak detection and diversion. This design is not suitable for CIP techniques and requires complete disassembly for manual cleaning. Compression valve (Fig. 23.2): this design uses a valve seat located on the end of a stem or rod that lifts the movable seat off a valve seat incorporated into the body of the valve. These valves operate efficiently when located in a variety of positions and have a large, unobstructed valve body to permit optimum flow through the valve. This design is generally suitable for CIP methods provided it is equipped with a power actuator that can be programmed to automatically pulse the valve seat during the cleaning cycle. Mixproof valve (Fig. 23.3): a mixproof valve is a specialized compression valve that uses double seats that can be operated independently, separated by a self-draining opening to the atmosphere between the valve seats. The primary design advantage of these valves is to accommodate the separation of two different product streams or product from cleaning fluids during CIP. Conformance of these valves to the United States, Food and Drug Administration requirements of the pasteurized milk ordinance requires specialized control units and a large vent passage. Diaphragm valve (Fig. 23.4): this design uses a flexible diaphragm to form the seal. The valves are used to shutoff or regulate product flow. They work well with semisolid and fluid products containing particulates. Diaphragm valves are not commonly used in dry product applications. The valves can be mechanically cleaned provided they are equipped with a power actuator and are installed properly to assure drainage of the valve body cavity. Many designs include an orientation mark on the housing to assist with installation. Tank outlet valve (Fig 23.5): outlet valves come in a variety of configurations depending on whether they are mounted horizontally or vertically. To eliminate or reduce the amount of product that may be retained in the outlet passage,
Handbook of Hygiene Control in the Food Industry. DOI: http://dx.doi.org/10.1016/B978-0-08-100155-4.00023-6 © 2016 Elsevier Ltd. All rights reserved.
337
338 PART | II Plant and Equipment
FIGURE 23.1 Plug valve.
FIGURE 23.2 Compression valve.
FIGURE 23.4 Diaphragm valve.
FIGURE 23.3 Mixproof valve.
FIGURE 23.5 Tank outlet valve.
Improving the Hygienic Design of Valves Chapter | 23 339
FIGURE 23.6 Pressure regulating valve.
FIGURE 23.7 Ball-type check valve.
●
●
●
●
●
FIGURE 23.8 Spring-loaded check valve.
the design provides for the valve to be as closely coupled as possible to the product vessel. They may be manually or mechanically operated and cleaned depending upon their design features. Pressure-reducing and regulating valve (Fig. 23.6): these valves are designed to control product pressure, either inlet or outlet, by responding to appropriate pressure changes by means of a self-acting actuator. The self-acting actuator raises or lowers the valve seat within the valve body by means of fluid forces within the valve body. Check valve (Figs. 23.7 and 23.8): check valves permit product flow in only one direction. A reversal of product flow or pressure will result in the valve sealing. The valve is self-actuating through the use of internal balls, valve flaps, or spring-loaded valve seats. Spring-loaded check valves must be fully disassembled for manual cleaning because of their basic design. However, some new designs provide additional actuators to facilitate CIP. Ball valve (Fig. 23.9): this design uses a ball connected to an actuation shaft. Product flow is directed or stopped through single or multiple passages within the ball. This design incorporates body cavity fillers or encapsulating seals to prevent product flow around the exterior of the ball. This design is not suitable for CIP techniques and requires complete disassembly for manual cleaning. Cage ball valve: this is a variation of the ball valve design. In this design, a solid ball is retained in a movable cage attached to an actuator shaft. Actuation of the valve positions the loosely retained ball so that the product pressure within the valve body causes the ball to block a port of the valve. The action is similar to that which occurs within a ball check valve. Depending upon the design of a specific model of valve, it may not be suitable for CIP. This style valve has not found widespread use. Pinch valve (Fig. 23.10): a pinch style valve consists of a flexible rubber or polymer liner within a metal tube. The flexible liner is pinched between metal components to restrict or stop the product flow.
340 PART | II Plant and Equipment
FIGURE 23.9 Ball valve.
FIGURE 23.10 Pinch valve.
23.2.2 Valves Used in Fluid or Dry Product Processing Systems ●
Blender discharge valve: blender discharge valves come in a variety of shapes and sizes according to the manufacturer of the blender. In most cases, the valves are located on the bottom or one end of the blender. They consist of either sliding gate types or hinged lift gate types. A pneumatic or hydraulic cylinder often powers the valve actuators. These designs require disassembly for cleaning.
Improving the Hygienic Design of Valves Chapter | 23 341
FIGURE 23.11 Dry products butterfly valve.
FIGURE 23.12 Rotary valve.
●
●
Butterfly valve (Fig. 23.11): this design utilizes a more-or-less flat, round disk attached on the edges of the disk to an actuator and support shaft. The shafts pass through a circular rubber or polymer seat that is clamped between two flanges. The valves can be set to regulate or block the flow through the valve. While often cleaned by CIP, this design will allow product to migrate along the shafts due to the product pressures in the system and should, therefore, be disassembled for manual cleaning. Rotary valve (Fig. 23.12): also known as a rotary airlock valve or a star valve, this consists of multiple vanes attached to a central shaft that rotates within a cylindrical housing. The valves are particularly efficient for transferring product between zones of differing pressure or vacuum. Some manufacturers have designed models specifically to meet the requirements for CIP. Designs that utilize bolted vane extenders or wiper blades are not suitable for CIP.
23.2.3 Valves Used in Dry Product Processing Systems ●
●
●
Iris valve (Fig. 23.13): an iris valve features a fabric or multisection metal diaphragm that opens or closes by a twisting motion of the valve’s outer housing similar to the action of a camera iris. Inflatable seal duct valve: these valves use a rubber bladder attached to the outer circumference of a valve disk or valve seat. After the valve is rotated into the closed position, the bladder is inflated to obtain a seal with the duct’s interior. Flip-flop valve (Fig. 23.14): a flip-flop valve has two movable valve disks or flaps, located one above the other, which cycle alternatively by mechanical means. Product is passed into the intermediate chamber between the two valve disks before passing through the valve body. Like rotary valves, flip-flop valves can transfer product between zones of differing pressure or vacuum.
342 PART | II Plant and Equipment
FIGURE 23.13 Iris valve.
FIGURE 23.14 Flip-flop valve.
Improving the Hygienic Design of Valves Chapter | 23 343
FIGURE 23.15 Diverter valve.
●
Diverter valve (Fig. 23.15): as its name implies, a diverter valve consists of two or more ports into which the product stream may be directed. Depending on the number of discharge ports provided, the actuating mechanism may be a simple flap valve, a positioning slide valve, or a rotary port plate.
23.3 HYGIENIC ASPECTS OF VALVE DESIGN The ubiquitous nature of valves within processing systems places them in a position to potentially have an impact on every particle of product passing through the system. Valves can be small or very large; simple or very complex in design. Therefore, their hygienic design is vital to producing a high-quality, safe product. Design plays a major role in whether or not a particular valve is suitable for its intended application. Valves that are intended to be mechanically cleaned or clean-in-place (CIP) require special design features. The design and operation during cleaning must assure that all components potentially contacted by product will also be contacted by cleaning and disinfection fluids (including hot water and steam) with sufficient turbulence or flow to thoroughly clean and decontaminate these areas. Generally speaking, any manually operated valve, regardless of its type or design, and valves used in dry product processing systems should not be considered as suitable for CIP methods. The inability for automatic cycling of the valve during cleaning prevents cleaning and sanitizing solutions from reaching all areas of the valve seats and other seals. These valves are only suitable for disassembly and manual cleaning.
344 PART | II Plant and Equipment
As with other equipment, hygienic design is based on such features as: ● ● ● ● ● ● ● ●
Materials of construction; Internal surface texture; Accessibility for cleaning and inspection (including leak detection and seat lifting); Draining; Elimination of cracks, crevices, and niches; Internal angles and corners; Dead areas; Process and installation concerns.
23.3.1 Materials of Construction Traditionally, hygienic valves for the food industry have been fabricated in stainless steel. The American Iron and Steel Institute (AISI) series 300 stainless steels and their equivalent cast grades have been the materials of choice for the metallic components of the valves. Nonmetallic components for seals, valve seats, diaphragms, plungers, and plug encapsulations are to be acceptable to the convening regulatory authority and be nontoxic, relatively inert, nonporous, nonabsorbent, and compatible with the environment of intended use, cleaning, and sanitization. Care must be exercised to assure that proper nonmetallic materials are selected; with particular emphasis on the fat content, cleaning and disinfection chemicals, and temperature ranges of the products intended to be processed.
23.3.2 Internal Surface Texture Product contact surface finishes at least as smooth as an Ra of 0.8 µm (32.0 micro-inch) on stainless steel free of imperfections such as pits, folds, and crevices in the final fabricated form have been proven to clean satisfactorily and are recognized by most hygienic equipment standards. Any deviations rougher than this minimum should be part of the manufacturer’s specifications so that the buyer can make an informed decision to use the valve.
23.3.3 Accessibility for Cleaning and Inspection The commonly used methods of cleaning are defined below. ●
●
●
Clean-in-place (CIP) cleaning: The removal of soil from product contact surfaces in their process position by circulating, spraying, or flowing chemical solutions and water rinses onto and over the surfaces to be cleaned. (Note: Components of the equipment, which are not designed to clean-in-place, are removed from the equipment to be manually cleaned.) Clean-out-of-place (COP) cleaning: Removal of soil when the equipment is partially or totally disassembled. Soil removal is effected by circulating chemical solutions and water rinses in a wash tank, which may be fitted with a circulating pump(s). Manual cleaning: Removal of soil when the equipment is partially or totally disassembled. Soil removal is effected by chemical solutions and water rinses with the assistance of one or a combination of brushes, nonmetallic scouring pads and scrapers, and high- or low-pressure hoses, with cleaning aids manipulated by hand.
The normal cycling of valves during processing and cleaning subjects valve components to high stress and wear of movable components. In large fluid lines, these stresses can force product pass seals or removable valve seats. Valves in dry product processes may be subjected to materials that are quite abrasive. Therefore, it is vital that valves be both accessible when installed in a processing system and easy to disassemble so that the wear and cleanliness of components can be periodically inspected. Valves that are supplied with automatic power actuators generally are required to have at least a 25 mm (1.0 inch) space between the actuator and the valve shaft seal that is open to atmosphere so that a failure of the seals is readily observable. Valves such as diaphragm or pinch valves that have internal components subject to failure require a drain opening to atmosphere to signal component failure. The drain opening is to be at a point low enough so that leaking product cannot collect within the valve housing.
Improving the Hygienic Design of Valves Chapter | 23 345
23.3.4 Draining Most valve designs have addressed the ability of the valve to be self-draining when properly installed. However, care must be exercised prior to installation, as some manufacturers still require attention to drainability of their designs. Upon installation of any multiport valve, care must be taken by the installer to assure that dead pockets are not created in the product flow when a port is closed. Some valve designs, such as most diaphragm valves, are inherently nonself-draining. In these cases, the valve should have a clearly identified orientation mark on the valve body to indicate proper installation angles. Self-draining is not a major consideration in dry product processes. These systems are designed to go for extended periods of time with only dry cleaning. In those rare instances where wet cleaning is necessary because of a contamination or a major maintenance project, the entire system, including any valves, must be disassembled to clean and thoroughly dry the wetted surfaces.
23.3.5 Elimination of Cracks, Crevices, and Niches Some valve designs, even with automatic actuators, are inherently not suitable for CIP methods. These designs tend to have large sliding seal areas as in plug, ball, iris, inflatable seal duct, and diverter type valves. The sliding seal will contain a film of product throughout production. The tolerances of the sliding seals prohibit the transport of sufficient cleaning and sanitizing fluids to achieve cleaning and decontamination. A valve’s design must take into consideration the proper attachment and compression of elastomeric components. The compression of the elastomeric components must be controlled so that the materials cannot be overcompressed, causing them to extrude into the product flow. Additionally, the compression must be sufficient to assure a tight seal across the full temperature range of processing, cleaning, and sterilization. The attachment of elastomeric components to metallic components shall assure that the intended flexing of the elastomeric components does not create crevices or cracks to open between the components as they are cycled. Lip seals within valves can be used only under special conditions where cleaning and sanitation have been validated and documented.
23.3.6 Internal Angles and Corners Sharp or decreasing internal angles and corners within a valve must be avoided to assure that hard-to-clean areas are not created in the design. This is especially important in valves that are subjected to manual cleaning procedures. The internal radii must be sufficiently large to allow for the cleaning implements to reach the surfaces. Generally, internal radii of 3 mm (1/8 inch) are recognized as adequate to accomplish cleaning. Smaller radii are permitted for smaller components within the valve. In these cases where smaller radii are required, they should not be less than 0.8 mm (0.032 inch). The manufacturer of the valve should specify the presence of such radii.
23.3.7 Process and Installation When designing a process system there are additional concerns that must be taken into consideration. Are there legal requirements of the regulatory authority? For example, pasteurization systems, including both batch and continuous systems, have special requirements for the valves used to segregate pasteurized from unpasteurized product. This may require special leak detection and rapid response times for valve actuation. Aseptic systems require valves that can be demonstrated to be bacteria-tight. Generally, valves will be designed for self-closure in the event of a power failure during processing. However, there may be instances where it is more beneficial for the valves to remain open so that the systems can self-drain. Therefore, care must be exercised in the selection of the valves and their placement within the system. It is quite common to use a “block and bleed” configuration of valves to assure separation of different streams (Fig. 23.16). Installers should pay extra attention to assure that the bleed lines properly drain and do not retain fluids. The food industry would be greatly helped by the availability of valves that provide the security of a “block and bleed” system while greatly simplifying draining, avoiding stagnant product. Installers must be careful not to create a common installation error that produces a “block–block–bleed” configuration. Care must also be exercised to assure that valves can be easily accessed for periodic maintenance and inspection. Valves commonly include components, which wear and require periodic replacement.
346 PART | II Plant and Equipment
FIGURE 23.16 Typical block and bleed valve configuration.
23.4 CURRENT GUIDELINES AND STANDARDS 3-A SSI, McLean, VA, 3-A Sanitary Standards numbers: 51- Plug-Type Valves, 53- Compression- Type Valves, 54- Diaphragm-Type Valves, 56- Inlet and Outlet Leak-Protector Plug-Type Valves, 58- Vacuum Breakers and Check Valves, 64- Pressure-Reducing and Back Pressure Regulating Valves, 66- Caged-Ball Valves, 68- Ball-Type Valves, and 85- Double-seat Mixproof Valves
FURTHER READING Grade A Pasteurized Milk Ordinance. US Department of Health and Human Services, Public Health Service, Food and Drug Administration. Hygienic Requirements of Valves For Food Processing, Doc 14, EHEDG, Dr Roland Cocker, member, EHEDG Valves subgroup, Hygienic design and assessment. New Food, 7 (1), 2004. Milk and Milk Product Equipment. A Guideline for Evaluating Construction, US Department of Health and Human Services, Public Health Service, Food and Drug Administration. USDA Guidelines for the Evaluation and Certification of the Sanitary Design and Fabrication of Dairy Processing Equipment, June 2001, US Department of Agriculture, Dairy Programs, Washington, DC.
Improving the Hygienic Design of Valves F. Tracy Schonrock Schonrock Consulting, Fairfax Station, VA, United States
23.1 INTRODUCTION Sanitary valves are ubiquitous throughout processing systems. Without them, modern processing systems would be cumbersome and inefficient. Valves provide operators with the ability to stop, direct, meter, and control the flow of products and ingredients throughout the process. Because of their widespread use, valve design and sanitation can impact on every particle of product passing through the process system.
23.2 VALVE TYPES Valves come in multiple configurations. They are well developed to operate in systems that process fluids, semifluids, fluids with particulates, viscous products, and dry products. Some valve designs operate well in more than one of these different environments.
23.2.1 Valves Commonly Used in Fluid Product Processing Systems The following are descriptions of valves commonly used in processing systems for fluid products, including viscous products and products with semisolid or solid particulates within the product stream. ●
●
●
●
●
●
Plug valve (Fig. 23.1): a simple design consisting of a tapered plug inserted into a tapered body. The valve can be configured as a shut-off valve or with one or more ports to direct flow to different product streams. The valves are most commonly manually operated but can be affixed with a power actuator. Plug valves are not generally used in dry product applications. This design is not suitable for clean-in-place (CIP) techniques and requires complete disassembly for manual cleaning. Leak protection valve: a leak protection valve is a specialized plug-type tank outlet valve that is used on vat pasteurization equipment. The design includes special features that will prevent leakage past the valve by controlling how far the valve may be turned and the inclusion of grooves to provide leak detection and diversion. This design is not suitable for CIP techniques and requires complete disassembly for manual cleaning. Compression valve (Fig. 23.2): this design uses a valve seat located on the end of a stem or rod that lifts the movable seat off a valve seat incorporated into the body of the valve. These valves operate efficiently when located in a variety of positions and have a large, unobstructed valve body to permit optimum flow through the valve. This design is generally suitable for CIP methods provided it is equipped with a power actuator that can be programmed to automatically pulse the valve seat during the cleaning cycle. Mixproof valve (Fig. 23.3): a mixproof valve is a specialized compression valve that uses double seats that can be operated independently, separated by a self-draining opening to the atmosphere between the valve seats. The primary design advantage of these valves is to accommodate the separation of two different product streams or product from cleaning fluids during CIP. Conformance of these valves to the United States, Food and Drug Administration requirements of the pasteurized milk ordinance requires specialized control units and a large vent passage. Diaphragm valve (Fig. 23.4): this design uses a flexible diaphragm to form the seal. The valves are used to shutoff or regulate product flow. They work well with semisolid and fluid products containing particulates. Diaphragm valves are not commonly used in dry product applications. The valves can be mechanically cleaned provided they are equipped with a power actuator and are installed properly to assure drainage of the valve body cavity. Many designs include an orientation mark on the housing to assist with installation. Tank outlet valve (Fig 23.5): outlet valves come in a variety of configurations depending on whether they are mounted horizontally or vertically. To eliminate or reduce the amount of product that may be retained in the outlet passage,
Handbook of Hygiene Control in the Food Industry. DOI: http://dx.doi.org/10.1016/B978-0-08-100155-4.00023-6 © 2016 Elsevier Ltd. All rights reserved.
337
338 PART | II Plant and Equipment
FIGURE 23.1 Plug valve.
FIGURE 23.2 Compression valve.
FIGURE 23.4 Diaphragm valve.
FIGURE 23.3 Mixproof valve.
FIGURE 23.5 Tank outlet valve.
Improving the Hygienic Design of Valves Chapter | 23 339
FIGURE 23.6 Pressure regulating valve.
FIGURE 23.7 Ball-type check valve.
●
●
●
●
●
FIGURE 23.8 Spring-loaded check valve.
the design provides for the valve to be as closely coupled as possible to the product vessel. They may be manually or mechanically operated and cleaned depending upon their design features. Pressure-reducing and regulating valve (Fig. 23.6): these valves are designed to control product pressure, either inlet or outlet, by responding to appropriate pressure changes by means of a self-acting actuator. The self-acting actuator raises or lowers the valve seat within the valve body by means of fluid forces within the valve body. Check valve (Figs. 23.7 and 23.8): check valves permit product flow in only one direction. A reversal of product flow or pressure will result in the valve sealing. The valve is self-actuating through the use of internal balls, valve flaps, or spring-loaded valve seats. Spring-loaded check valves must be fully disassembled for manual cleaning because of their basic design. However, some new designs provide additional actuators to facilitate CIP. Ball valve (Fig. 23.9): this design uses a ball connected to an actuation shaft. Product flow is directed or stopped through single or multiple passages within the ball. This design incorporates body cavity fillers or encapsulating seals to prevent product flow around the exterior of the ball. This design is not suitable for CIP techniques and requires complete disassembly for manual cleaning. Cage ball valve: this is a variation of the ball valve design. In this design, a solid ball is retained in a movable cage attached to an actuator shaft. Actuation of the valve positions the loosely retained ball so that the product pressure within the valve body causes the ball to block a port of the valve. The action is similar to that which occurs within a ball check valve. Depending upon the design of a specific model of valve, it may not be suitable for CIP. This style valve has not found widespread use. Pinch valve (Fig. 23.10): a pinch style valve consists of a flexible rubber or polymer liner within a metal tube. The flexible liner is pinched between metal components to restrict or stop the product flow.
340 PART | II Plant and Equipment
FIGURE 23.9 Ball valve.
FIGURE 23.10 Pinch valve.
23.2.2 Valves Used in Fluid or Dry Product Processing Systems ●
Blender discharge valve: blender discharge valves come in a variety of shapes and sizes according to the manufacturer of the blender. In most cases, the valves are located on the bottom or one end of the blender. They consist of either sliding gate types or hinged lift gate types. A pneumatic or hydraulic cylinder often powers the valve actuators. These designs require disassembly for cleaning.
Improving the Hygienic Design of Valves Chapter | 23 341
FIGURE 23.11 Dry products butterfly valve.
FIGURE 23.12 Rotary valve.
●
●
Butterfly valve (Fig. 23.11): this design utilizes a more-or-less flat, round disk attached on the edges of the disk to an actuator and support shaft. The shafts pass through a circular rubber or polymer seat that is clamped between two flanges. The valves can be set to regulate or block the flow through the valve. While often cleaned by CIP, this design will allow product to migrate along the shafts due to the product pressures in the system and should, therefore, be disassembled for manual cleaning. Rotary valve (Fig. 23.12): also known as a rotary airlock valve or a star valve, this consists of multiple vanes attached to a central shaft that rotates within a cylindrical housing. The valves are particularly efficient for transferring product between zones of differing pressure or vacuum. Some manufacturers have designed models specifically to meet the requirements for CIP. Designs that utilize bolted vane extenders or wiper blades are not suitable for CIP.
23.2.3 Valves Used in Dry Product Processing Systems ●
●
●
Iris valve (Fig. 23.13): an iris valve features a fabric or multisection metal diaphragm that opens or closes by a twisting motion of the valve’s outer housing similar to the action of a camera iris. Inflatable seal duct valve: these valves use a rubber bladder attached to the outer circumference of a valve disk or valve seat. After the valve is rotated into the closed position, the bladder is inflated to obtain a seal with the duct’s interior. Flip-flop valve (Fig. 23.14): a flip-flop valve has two movable valve disks or flaps, located one above the other, which cycle alternatively by mechanical means. Product is passed into the intermediate chamber between the two valve disks before passing through the valve body. Like rotary valves, flip-flop valves can transfer product between zones of differing pressure or vacuum.
342 PART | II Plant and Equipment
FIGURE 23.13 Iris valve.
FIGURE 23.14 Flip-flop valve.
Improving the Hygienic Design of Valves Chapter | 23 343
FIGURE 23.15 Diverter valve.
●
Diverter valve (Fig. 23.15): as its name implies, a diverter valve consists of two or more ports into which the product stream may be directed. Depending on the number of discharge ports provided, the actuating mechanism may be a simple flap valve, a positioning slide valve, or a rotary port plate.
23.3 HYGIENIC ASPECTS OF VALVE DESIGN The ubiquitous nature of valves within processing systems places them in a position to potentially have an impact on every particle of product passing through the system. Valves can be small or very large; simple or very complex in design. Therefore, their hygienic design is vital to producing a high-quality, safe product. Design plays a major role in whether or not a particular valve is suitable for its intended application. Valves that are intended to be mechanically cleaned or clean-in-place (CIP) require special design features. The design and operation during cleaning must assure that all components potentially contacted by product will also be contacted by cleaning and disinfection fluids (including hot water and steam) with sufficient turbulence or flow to thoroughly clean and decontaminate these areas. Generally speaking, any manually operated valve, regardless of its type or design, and valves used in dry product processing systems should not be considered as suitable for CIP methods. The inability for automatic cycling of the valve during cleaning prevents cleaning and sanitizing solutions from reaching all areas of the valve seats and other seals. These valves are only suitable for disassembly and manual cleaning.
344 PART | II Plant and Equipment
As with other equipment, hygienic design is based on such features as: ● ● ● ● ● ● ● ●
Materials of construction; Internal surface texture; Accessibility for cleaning and inspection (including leak detection and seat lifting); Draining; Elimination of cracks, crevices, and niches; Internal angles and corners; Dead areas; Process and installation concerns.
23.3.1 Materials of Construction Traditionally, hygienic valves for the food industry have been fabricated in stainless steel. The American Iron and Steel Institute (AISI) series 300 stainless steels and their equivalent cast grades have been the materials of choice for the metallic components of the valves. Nonmetallic components for seals, valve seats, diaphragms, plungers, and plug encapsulations are to be acceptable to the convening regulatory authority and be nontoxic, relatively inert, nonporous, nonabsorbent, and compatible with the environment of intended use, cleaning, and sanitization. Care must be exercised to assure that proper nonmetallic materials are selected; with particular emphasis on the fat content, cleaning and disinfection chemicals, and temperature ranges of the products intended to be processed.
23.3.2 Internal Surface Texture Product contact surface finishes at least as smooth as an Ra of 0.8 µm (32.0 micro-inch) on stainless steel free of imperfections such as pits, folds, and crevices in the final fabricated form have been proven to clean satisfactorily and are recognized by most hygienic equipment standards. Any deviations rougher than this minimum should be part of the manufacturer’s specifications so that the buyer can make an informed decision to use the valve.
23.3.3 Accessibility for Cleaning and Inspection The commonly used methods of cleaning are defined below. ●
●
●
Clean-in-place (CIP) cleaning: The removal of soil from product contact surfaces in their process position by circulating, spraying, or flowing chemical solutions and water rinses onto and over the surfaces to be cleaned. (Note: Components of the equipment, which are not designed to clean-in-place, are removed from the equipment to be manually cleaned.) Clean-out-of-place (COP) cleaning: Removal of soil when the equipment is partially or totally disassembled. Soil removal is effected by circulating chemical solutions and water rinses in a wash tank, which may be fitted with a circulating pump(s). Manual cleaning: Removal of soil when the equipment is partially or totally disassembled. Soil removal is effected by chemical solutions and water rinses with the assistance of one or a combination of brushes, nonmetallic scouring pads and scrapers, and high- or low-pressure hoses, with cleaning aids manipulated by hand.
The normal cycling of valves during processing and cleaning subjects valve components to high stress and wear of movable components. In large fluid lines, these stresses can force product pass seals or removable valve seats. Valves in dry product processes may be subjected to materials that are quite abrasive. Therefore, it is vital that valves be both accessible when installed in a processing system and easy to disassemble so that the wear and cleanliness of components can be periodically inspected. Valves that are supplied with automatic power actuators generally are required to have at least a 25 mm (1.0 inch) space between the actuator and the valve shaft seal that is open to atmosphere so that a failure of the seals is readily observable. Valves such as diaphragm or pinch valves that have internal components subject to failure require a drain opening to atmosphere to signal component failure. The drain opening is to be at a point low enough so that leaking product cannot collect within the valve housing.
Improving the Hygienic Design of Valves Chapter | 23 345
23.3.4 Draining Most valve designs have addressed the ability of the valve to be self-draining when properly installed. However, care must be exercised prior to installation, as some manufacturers still require attention to drainability of their designs. Upon installation of any multiport valve, care must be taken by the installer to assure that dead pockets are not created in the product flow when a port is closed. Some valve designs, such as most diaphragm valves, are inherently nonself-draining. In these cases, the valve should have a clearly identified orientation mark on the valve body to indicate proper installation angles. Self-draining is not a major consideration in dry product processes. These systems are designed to go for extended periods of time with only dry cleaning. In those rare instances where wet cleaning is necessary because of a contamination or a major maintenance project, the entire system, including any valves, must be disassembled to clean and thoroughly dry the wetted surfaces.
23.3.5 Elimination of Cracks, Crevices, and Niches Some valve designs, even with automatic actuators, are inherently not suitable for CIP methods. These designs tend to have large sliding seal areas as in plug, ball, iris, inflatable seal duct, and diverter type valves. The sliding seal will contain a film of product throughout production. The tolerances of the sliding seals prohibit the transport of sufficient cleaning and sanitizing fluids to achieve cleaning and decontamination. A valve’s design must take into consideration the proper attachment and compression of elastomeric components. The compression of the elastomeric components must be controlled so that the materials cannot be overcompressed, causing them to extrude into the product flow. Additionally, the compression must be sufficient to assure a tight seal across the full temperature range of processing, cleaning, and sterilization. The attachment of elastomeric components to metallic components shall assure that the intended flexing of the elastomeric components does not create crevices or cracks to open between the components as they are cycled. Lip seals within valves can be used only under special conditions where cleaning and sanitation have been validated and documented.
23.3.6 Internal Angles and Corners Sharp or decreasing internal angles and corners within a valve must be avoided to assure that hard-to-clean areas are not created in the design. This is especially important in valves that are subjected to manual cleaning procedures. The internal radii must be sufficiently large to allow for the cleaning implements to reach the surfaces. Generally, internal radii of 3 mm (1/8 inch) are recognized as adequate to accomplish cleaning. Smaller radii are permitted for smaller components within the valve. In these cases where smaller radii are required, they should not be less than 0.8 mm (0.032 inch). The manufacturer of the valve should specify the presence of such radii.
23.3.7 Process and Installation When designing a process system there are additional concerns that must be taken into consideration. Are there legal requirements of the regulatory authority? For example, pasteurization systems, including both batch and continuous systems, have special requirements for the valves used to segregate pasteurized from unpasteurized product. This may require special leak detection and rapid response times for valve actuation. Aseptic systems require valves that can be demonstrated to be bacteria-tight. Generally, valves will be designed for self-closure in the event of a power failure during processing. However, there may be instances where it is more beneficial for the valves to remain open so that the systems can self-drain. Therefore, care must be exercised in the selection of the valves and their placement within the system. It is quite common to use a “block and bleed” configuration of valves to assure separation of different streams (Fig. 23.16). Installers should pay extra attention to assure that the bleed lines properly drain and do not retain fluids. The food industry would be greatly helped by the availability of valves that provide the security of a “block and bleed” system while greatly simplifying draining, avoiding stagnant product. Installers must be careful not to create a common installation error that produces a “block–block–bleed” configuration. Care must also be exercised to assure that valves can be easily accessed for periodic maintenance and inspection. Valves commonly include components, which wear and require periodic replacement.
346 PART | II Plant and Equipment
FIGURE 23.16 Typical block and bleed valve configuration.
23.4 CURRENT GUIDELINES AND STANDARDS 3-A SSI, McLean, VA, 3-A Sanitary Standards numbers: 51- Plug-Type Valves, 53- Compression- Type Valves, 54- Diaphragm-Type Valves, 56- Inlet and Outlet Leak-Protector Plug-Type Valves, 58- Vacuum Breakers and Check Valves, 64- Pressure-Reducing and Back Pressure Regulating Valves, 66- Caged-Ball Valves, 68- Ball-Type Valves, and 85- Double-seat Mixproof Valves
FURTHER READING Grade A Pasteurized Milk Ordinance. US Department of Health and Human Services, Public Health Service, Food and Drug Administration. Hygienic Requirements of Valves For Food Processing, Doc 14, EHEDG, Dr Roland Cocker, member, EHEDG Valves subgroup, Hygienic design and assessment. New Food, 7 (1), 2004. Milk and Milk Product Equipment. A Guideline for Evaluating Construction, US Department of Health and Human Services, Public Health Service, Food and Drug Administration. USDA Guidelines for the Evaluation and Certification of the Sanitary Design and Fabrication of Dairy Processing Equipment, June 2001, US Department of Agriculture, Dairy Programs, Washington, DC.