Guide to Inspections of Low Acid Canned Food 21
Manufacturers - 2
important to proper temperature distribution. A gate valve can normally be recognized by a long stem, by the number of turns of the valve stem that it takes to close the valve (more turns are needed for a gate as compared to a globe valve), and sometimes by the appearance of the outside of the valve body (more square when compared to a rounded globe valve). If the gate valve cannot be identified in this manner the valve stem may have to be removed to identify the type of valve.
- GLOBE VALVE - Globe valves are extensively used for the control of flow and where positive shut off is required. A globe valve employs an internal seat within the valve body. Hand operated globe valves are operated by turning the valve stem counter clockwise to open the valve and clockwise to close the valve. Threads on the valve stem cause the seal on the valve stem to mate with or move away from the valve seat. Close control over flow is readily accomplished. As the fluid or gas moves through this type of valve it must change direction. This results in increased resistance to flow. For this reason this type of valve is not ideal for venting of steam retorts. Globe valves are ideal for use on water and air lines where close control over flow is required. Globe valves have a positive shut off feature which can prevent leakage of air and water into retorts during processing.
- BALL VALVE - Ball valves are quick opening, full flow valves, needing only a quarter of a turn to be fully open. A ball with a non-restricting port rides in a valve body on plastic non-sticking seats. Ball valves can provide a bubble tight seal. The ball valve can be used for full flow (venting), and control (water and air supply) functions on retorts.
- BUTTERFLY VALVE - Butterfly valves are quick opening, full flow valves which employ a metal disk which when rotated on a shaft seals against seats in the valve body. Butterfly valves are normally used as throttling valves to control flow. Butterfly valves may be found on some of the newer retort systems
- DIAPHRAGM VALVE - Diaphragm valves contain a moveable diaphragm within the valve body which fits against a valve body seat. When the diaphragm is raised or lowered by the valve stem flow is increased or decreased through the valve. Diaphragm valves may be found on some of the newer retort systems.
Valves may be operated by hand, pneumatically (by air, steam or other gas), electrically (by a solenoid or motor) or by a combination of these methods.
Free flow valves such as the gate or ball valve are normally used on steam retort vent lines. The use of globe or other type valves on steam retort vent lines is not prohibited by the lacf regulations. If these types of valves are used, temperature distribution studies are required to document adequate temperature distribution in the retort prior to the start of the thermal process.
Valves which provide a tight seal, such as the globe or ball valve must be used on air and water lines to prevent leakage into the retort during thermal processing. Valve seats and seals must be maintained to prevent the valves from leaking. During a lacf inspection the retort should be examined for evidence of leaking water and air valves. Some firms may employ the use of double valves on air and water lines to insure that no air or water is leaked into the retort during processing.
Temperature distribution is the work performed to ensure that the retort instrumentation accurately reflects that adequate temperature distribution has been achieved throughout the retort at the time that the sterilization cycle begins. This is accomplished by distributing an adequate number of thermocouples or other temperature measuring devices (TMDs) throughout the load (external to the containers), and making several runs or tests to ensure that temperature differences have been minimized. The number of thermocouples (TMDs) to be used is normally limited by the equipment available. A minimum of 12 thermocouples has been suggested by The Institute for Thermal Processing Specialists. With large retort systems and numerous retort crates a greater number of thermocouples may allow for a more extensive test to be completed. At least one thermocouple is placed next to the MIG thermometer and used as a reference during the study. The worst case situation for temperature distribution normally occurs when heat flow to the product is the greatest. The heat absorption rate of a convection heating (heat currents are formed in the container) is much higher than a conduction heating (heat must penetrate through the material) product. It is normally suggested that a convection heating product in the smallest container processed or a special cold water pack be used to test temperature distribution in still retorts. Other conditions may present the worst case for temperature distribution in a specific retort system or for a specific product or container type. This must be documented in the temperature distribution study. In some retort systems temperature distribution tests must be