Cream, cheese in all its many forms, yogurt, and ice cream are just some of the various dairy products that many of us consume daily. Milk, and most of the products it's made into, is moved through pipes. These need regular and thorough cleaning to avoid any risk to human health, and that creates some challenges in terms of the types of valves used.
Hygiene in the dairy industry
Cleanliness is important when processing any food, but especially so for milk products. Milk can harbor pathogens that thrive in warm conditions, and it has a tendency to cling to surfaces. To guard against contamination, the dairy industry follows the “Grade A Pasteurized Milk Ordinance,” often shortened to PMO.
PMO addresses both the materials and components used in dairy production, as well as the cleaning processes. Almost all dairy producers follow Clean in Place, or CIP, procedures for cleaning pipes, tanks, and valves. (The alternative is to disassemble systems, clean the parts, and then put it all back together. That process is slower and not as effective.)
CIP mandates cleaning by steam and/or caustic solutions. In addition, all the piping systems must be mix-proof. This is to avoid any cross-contamination of the milk or other dairy products.
Valves for the dairy industry
Let's start with what's not used: ball valves. You won't find any of these in the dairy industry. That's because it's very difficult for CIP procedures to get ball valves completely sterile. You also won’t see butterfly valves in U.S. production. Instead, what you have are variants of dome valves.
These are used for shutoff and flow control. Some are termed change-over valves and meet PMO requirements by incorporating a double seat or double seal design plus additional ports that keep product and cleaning solution separate.
Constant pressure valves are also common in dairy production, often used after separators and pasteurizers and immediately before filling machines.
As far as materials for dairy systems are concerned, it's pretty much stainless throughout: both 304 and so-called “acid proof” 316 grade are used for valves, pipes, and tanks.
One feature you might not expect is an emphasis on how the products flow. First, while milk is a low viscosity fluid, products such as cream and yogurt are thicker and flow more slowly. Second, dairy producers are usually anxious to avoid any “shear” in the fluid as it flows. This is because shear (a result of turbulent mixing) creates an inconsistent product.
To counteract shear, dairy plumbing systems are designed with larger diameters than used elsewhere and an emphasis on minimizing pressure drops and turbulence. This ensures your cottage cheese or Greek yogurt has the consistency you expect.
Flow management, but with differences
Whether you're piping water, milk, or even nitrogen gas, fluids all flow according to the same laws of physics. The differences in how piping systems are designed arise from the particular nature of each specific fluid.
As discussed here, dairy products present an especially interesting challenge. Not only are the requirements for cleanliness extremely demanding, but the way in which the product flows must also be considered.