How to Select Sanitary Fittings
Image Credit: Knick Elektronische Messgeraete GmbH & Co. KG | Qosina Corp. | Hayward Flow Control
Sanitary fittings are designed and constructed for use in food, beverage, medical, pharmaceutical, and biological applications where cleanliness and sterility are required. These types of fittings are constructed of materials that ensure a sterile environment and maintain sterility during use.
Fittings are categorized based on the three different types of vessels they can be designed for: hoses, pipes, and tubes.
Pipes are hollow cylinders of uniform material with a certain amount of rigidity and permanence. Pipe sizes are defined nominally, meaning the actual dimensions (inner diameter, wall thickness) may vary from based on standard pipe sizes and pipe schedules from ANSI / ASME and API, where:
ANSI - American National Standards Institute
ASME - American Society of Mechanical Engineers
API - American Petroleum Institute
Tubes and pipes are often interchangeable in industry, the main difference typically being how their dimensions are specified. Generally, tubes and their fittings are defined with exact rather than nominal dimensions. In other words, a tube's outer diameter will often measure exactly 1.5 inches if rated with a 1.5" OD.
Hoses are generally considered different from pipes and tubes. They are typically more flexible and portable, and are often made up of multiple layers of different materials which vary based on the application.
Types of Fittings
Every sanitary fitting can be classified based on the connection type and function it performs.
Fittings are attached to tubes, pipes, or hoses via a number of different connection methods, each with its own conveniences and advantages.
Ball and sleeve fittings - Connects an outer sleeve to an inner (ball) fitting. The sleeve retracts to connect and disconnect the two ends of the fitting.
Barbed fittings - Connects hose flexible tubing via a barbed end with a tapered stub and ridges inserted into the vessel. They are best suited for low pressure applications, since they do not provide a strong seal.
Cam-lock fittings - Connected using tabs which fold down into the receiver to lock the fitting in place after insertion. They are used in many heavy-duty applications such as fire hose and sludge/sewage pumping.
Compression fittings - Connect vessels using compression on a gasket, ring, or ferrule.
Crimp fittings - Involve placing a vessel over a tubular end and crimping against it with a sleeve or crimp socket. These fittings typically require crimping tools to make the connections.
End fittings - Provide specific end surfaces for making connections
- Clamp ends are fittings which allow vessels (typically hose) to be clamped to the connection.
- Plain ends are fittings which allow vessels to be connected by adhesive, solder, or other forms.
Flanges - Ports with flush surfaces perpendicular to the attached vessel. These surfaces are joined and sealed via clamps, bolts, and/or welding. When connecting tubes and pipes, these fittings are attached separately to the vessel ends. Flange connections in hose are typically built in.
Luer locks - Sleeve fittings that afford simple, effective connections (generally for short, single use) by a quick twisting action. They are most commonly used to connect tubes in medical and laboratory applications.
Push-on (quick connect) fittings - Fittings which have ends designed to accept vessels by pushing them into the end. These fittings typically disconnect via some type of collar retraction. Quick connections are convenient for sections of the system requiring frequent disconnection and reconnection during operation.
Threaded fittings - Fittings with screw threads (built-in grooves) on their inner (female) or outer (male) surfaces designed to accept tubing with matching threads.
There are a variety of different fitting types, each which performs one of several basic functions.
Fittings which extend or terminate:
Adapter - Connects two dissimilar vessels to each other via solvent welding, soldering, or threading.
Coupling - Connects two similar vessels to each other via solvent welding, soldering, or threading.
Sleeve - Connect two vessels to each other using mechanical fasteners (e.g. screws, anchors).
Union - Coupling which can be disconnected without cutting.
Cap - Covers the end of a vessel, attaching on the male end via welded or threaded connection.
Plug - Closes off the end of a vessel, attaching on the female end via welded or threaded connection.
Fittings which add or change direction:
- Elbow - Changes the direction of the vessel to various angles. Most common angles are 90° and 45°, but 22.5° elbows are also made.
Tee - Connects three sections in a T-shaped intersection. This allows fluid flow to be combined or split apart.
Wye - Connects three sections in a Y-shaped intersection. They combine or split apart fluid flow like tees, but with less resistance.
Cross - 4-way connections, providing one inlet and three outlets or vice versa. Crosses are less steady than tees, and can generate high stress on the vessel with temperature changes.
Fittings which change vessel size:
Reducer - Includes all fittings which connect between two or more vessels of different sizes.
Olet - Reduction fitting attached to branched connections when adequate reducing tees or crosses are not available.
Fittings which provide special connections or functions:
Nipple - Allows two separate fittings to be connected at each end. Standard nipples are straight with male threads on both ends.
Valve - Connects vessels together with the addition of a valve for the control of flow.
Once the type of fitting required has been determined, the most fundamental aspect of sanitary fittings can be addressed: proper sizing. Proper sizing is essential to successful fitting selection, as oversized or undersized parts will either be completely incompatible or will seal or connect inadequately.
The two systems of measurement are Metric (mm) and English ("). The first step to proper sizing is selecting the appropriate measurement system for compatibility with the equipment or assemby being fitted.
The sizing of a fitting is defined by the inside diameter (ID) and outside diameter (OD) of its corresponding connections, measured in inches (in) or millimeters (mm). In other words, a fitting designed to connect to a tube with a 2" OD is rated as a 2" OD fitting. Inside diameter measures the diameter of the empty portion of the cylinder, while outside diameter includes the thickness of the vessel wall, as pictured below:
ID and OD measurements. Image Credit: Engineering Toolbox
The operating specifications that are most important for fittings are pressure and temperature.
- Operating pressure range is the working range of pressures or the pressure ratings at which the fitting was designed to operate, typically measured in pounds per square inch (psi). Operating above or below this rating could cause the fitting to fail (i.e. break, leak, lose its seal).
- Operating temperature range is the working range of temperatures or the temperature ratings at which the fitting was designed to operate, measured in degrees Fahrenheit (°F) or degrees Celsius (°C). Operating above or below this rating could cause the fitting to fail.
Material is an important factor in sanitary fitting selection. Fitting material considered 'sanitary' must be sterilizable and be able to handle repeated exposure to high temperature steam, pressure, and strong chemicals. Fittings must also be compatible with the material of the vessel (tube, pipe, or hose) they are attached to. Often this means that the fitting material matches the material used for the vessel, especially in the case of metals.
Stainless steel is an alloy of steel that contains a minimum of 10.5% chromium which provides superior corrosion resistance and antibacterial properties compared to standard steels, allowing it to withstand rigorous cleaning and sanitation processes without rusting or degrading. It also has strength and hardness properties similar to other steel alloys. In sanitary applications, stainless steel is the most common material used for fittings.
Polytetrafluoroethylene (PTFE) is a fluorocarbon-based polymer commonly known by the DuPont brand name Teflon®. It offers high chemical resistance, resistance to weathering, low friction, electrical and thermal insulation, and "slipperiness". PTFE's mechanical properties are low compared to other plastics, but they remain at a useful level over a wide temperature range of -100°F to +400°F (-73°C to 204°C). Mechanical properties are often enhanced by adding fillers. It is typically the best choice for applications involving highly corrosive liquids such as hydrochloric acid.
Polyvinylidene fluoride (PVDF) is a fluoropolymer also known by its brand name Kynar. It has a recommended maximum continuous use temperature of 150°C (302°F). It exhibits excellent mechanical strength and toughness, stiffness, high dielectric strength, abrasion resistance, creep resistance, high purity, chemical inertness, low flammability, and low moisture absorption. These properties make PVDF the preferred fitting material for applications in the semiconductor and chemical processing industry.
Polypropylene is a thermoplastic material that exhibits excellent cold flow, bi-axial strength, and yield elongation properties. It is similar to PVC, but can be used in exposed applications because of its resistance to UV, weathering, and ozone.
It may be important to select a sanitary fitting which incorporates one or more of a number of important features:
Valve fittings are those which incorporate valves to allow shutoff or flow control at the point of connection. Specific designations include:
Single shut-off -
Double shut-off - Both the plug and the coupler have valves for providing shutoff to maintain fluid pressure when disconnected.
Nonspill - Nonspill, self-cleaning, flush-face valve design minimizes fluid loss. The coupler incorporates a fluid trapping door that is flush with coupler face when disengaged.
Flexible fittings have the ability to move without being damaged.
Pre-insulated fittings consist of insulating materials or jacket constructions designed to insulate the vessel and media from outside temperatures.
Lined fittings are manufactured with an integral lining. The linings are often made from engineered polymers for use with process materials or in applications such as food processing where media cleanliness is important.
Swivel feature allows one or more fitting ends to rotate or swivel.
Expansion joints and couplings connect sections of tube and provide allowance for movement due to service load, shock, or thermal cycles.
Bullhead fittings are in a T-shape, in which the branch port is larger than the run ports.
Bulkhead fittings are designed to be mounted in a wall or bulkhead to allow tube connections on either side of barrier.
Some applications may require sanitary fittings that comply with certain regulation standards. Some of these standards include:
3-A Certification - 3-A Sanitary Standards, Inc. (3-A SSI) is an independent corporation dedicated to advancing hygienic equipment designed for the food, beverage, and pharmaceutical industries.
FDA Standards - The Food and Drug Administration (FDA) has regulations for "food contact materials"-- materials that are intended to be in contact with food. Most of these standards are outline under 21 CFR 170-199.
USDA Standards - The US Department of Agriculture (USDA) has standards for the proper production of sanitary food products such as dairy.
USP Standards - The United States Pharmacopeia (USP) is a non–governmental, official public standards–setting authority for prescription and over–the–counter medicines and other healthcare products manufactured or sold in the United States.
NSF International Standards - The Public Health and Safety Company™, a not-for-profit, non-governmental organization, is the world leader in standards development, product certification, education, and risk-management for public health and safety.
Selection Tip: Often manufacturers which sell certified parts will provide documentation of certification upon request that indicates its compliance with regulation standards.
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