Before the advent of thermoplastic fittings, the water conditioning industry was basically limited to brass, bronze, galvanized and copper tubing for connecting Point-of-Entry (POE) filters, softeners and related components to service plumbing. Point-of-Use (POU) drinking water appliances were typically fitted up with brass compression fittings and copper or polyethylene tubing.
In the mid-1980s, plastic push-fit type fittings were introduced to the US water conditioning market and shortly thereafter, drinking water systems were marketed with these new fittings. This was followed closely by small Reverse Osmosis (RO) systems that incorporated pumps to improve applied pressure to the membrane where high TDS and/ or low feed water pressure conditions were present. Excitement among product assemblers, manufacturers, installers and service departments was high because of the speed with which tube connections and water service could be made. Then, reality set in.
Some early adopters of the push-fit type fittings, especially assemblers of the small, pump-equipped RO systems, quickly learned a lesson in paying attention to the application guidelines for those new fittings. They were not designed to work in a negative pressure (vacuum) application. To be more specific, it was found that fitting the inlet port of a rotary vane pump with this fitting would allow a vacuum on startup and it could be observed that air was being drawn from the atmosphere and joining the influent water stream. The result was a failure of the rotary vane pump due to cavitation created by the entrained air.
A locking clip for the collet was quickly provided by the fitting manufacturer that prevented this condition. It was an expensive and hard lesson learned by those who rushed to be first, ignoring the user responsible for making the final selection of materials, accessories, and components which would have prevented misapplication of the product.
Now, over 30 years since that product introduction, advances in fitting design have improved and there are many manufacturers competing for this fitting business in many different markets and applications, including:
With so many market inroads, it’s important to know what the limitations are for various types of fittings, valves, tubing, and accessories used for specific applications. Let’s look at some application conditions that must be considered before the final selection of thermoplastic fittings and tubing for water and beverage service compatibility.
Since the application involves drinking water, the selection process must include Instrument Grade FDA and NSF 51 and/or NSF 61 standards compliance. This will quickly narrow down the field of qualified fittings, valves, and tubing. A material selection guide is typically provided by the manufacturer and is recommended for review to confirm the accurate selection of components for the application under consideration.
What is the expected system pressure?
This is important, especially when measuring the static water pressure in the service plumbing of a residence, office or commercial/industrial building. Use a faucet-mounted pressure gauge to obtain the water pressure. Another option is to contact the local water utility and ask for the average and highest known water pressure for the grid area where the installation will be commissioned. Where excessive pressures are recorded, specify a properly rated pressure reducing valve on the inlet of the installation to ensure compliance with the recommended working pressure of the tubing. Working pressures of fittings and valves are typically much higher than that of tubing but still should not be overlooked when specifying the overall material list.
What is the expected maximum temperature for the application? Is there a hot-water circuit included in the specification?
Look closely at the working pressure (WP) of the selected tubing to make sure it is within the temperature and pressure ranges specified by the manufacturer. There will be a temperature and pressure chart for the tubing to confirm what the maximum allowable system pressure is relative to the maximum water temperature. Read this chart and make sure you are referencing the specific size tubing you have specified. Smaller diameter tubing will operate at both higher pressure and temperature than larger diameter tubing.
For example, a 3/8-inch OD polyethylene tube will operate at 77 psi at 125°F, whereas a 5/8-inch OD polyethylene tube at the same temperature specifies a recommended working pressure of only 43 psi. Therefore, a 0.625-inch OD polypropylene tube would be recommended because that size tube will operate at up to 100 psi at 125°F. Polypropylene tube is more rigid than polyethylene and is designed for higher pressure and temperature.
Do not design your system based on the minimum burst pressure rating in the application chart. The working pressure is typically one-third of the minimum burst pressure; use caution and confirm that you are specifying your tubing based on the recommended working pressure. If a change to a polypropylene tube is required, it is very important to confirm compatibility with the tube fitting. Some fittings are only rated for polyethylene tube, so use extra caution here. Additionally, tube support is recommended for these types of tubing for maximum holding power where end loading, vibration or pressure spikes may occur. A good example of this would be where a solenoid valve in the system controls the flow. The opening and closing of the valve will create pressure spikes that could result in connection failure.
What are the environmental conditions in and around the installation site?
Let’s assume the installation is a casual dining restaurant where food is prepared along with water, soft drinks, ice, coffee and hot water for tea. POU water filtration is provided to improve aesthetics and eliminate taste and odor from a chlorinated municipal water source. This filtered water is supplied to the various fixtures and dispensers from this central filter. Each may require a different size supply-tube connection. In this case, the service line from the filter would be a 0.500- or 0.625-inch OD with 0.375- and 0.25-inch branch connections to the various connections. Careful attention to the routing of the tubing for this facility is important, not only for the protection of the quality of the water but also for the safety of the kitchen and wait staff. In some areas, it may be necessary to run the tubing through a rigid [pipe] chase to protect the softer tubing from potential damage during routine activities in the restaurant.
If the tubing is exposed to a continuously lighted area, it is advisable to use colored tubing to prevent light transmission into the water. Natural (clear) tubing is not recommended because light transmission into the water can allow algae growth, which would be a health code violation and would contribute to bad tasting water.
Tubing that will be routed near hot water lines should be insulated to prevent heat transfer into the tubing which could, in turn, cause tube failure and possible water damage. Where tubing is exposed to direct sunlight, the tubing should be rated for UV light resistance to prevent degradation and potential failure.
Tubing should also be secured with appropriate safety clips on fittings and routed in a manner that does not create an occupational or safety hazard.
What cleaning agents are used that might affect corrosion resistance?
Cleaning agents must also be considered for a food-service establishment where corrosive oxidizers and degreasers are used, to maintain antibacterial conditions in the food preparation areas. Corrosion-resistant fittings made of polypropylene or Kynar are recommended for these areas whereas acetal fittings will degrade quickly when exposed to corrosive cleaning agents and/or fumes.
Tubing, fittings, and valves that are exposed to foot traffic, run over or impacted in any way are exposed to hostile conditions that could precipitate into a failure of the installation or injury to an employee or patron. Sometimes it may be necessary to route tubing up and over a doorway or even above a drop-ceiling to avoid these kinds of hostile conditions.
What is the maintenance and service of the system after installation, startup, and commissioning?
Routine inspection of the tubing and fittings should be scheduled and any repairs or reconfiguration made if problems arise. Other service contractors or equipment suppliers may cause damage (unintentionally of course) to your system during installation, service/maintenance or removal of equipment, or other related activities that may not be immediately realized until some of the connected fixtures or machines fail to provide the filtered water. Designing the tube routing system in a way that allows prompt and efficient service and/or maintenance should always be at the forefront of this type of installation. Unscheduled downtime in a food service establishment is sorely frowned upon, especially if care is not exercised during the system installation. Take care to protect fittings, valves, and tubing from mishaps that could and should be avoided with thoughtful planning and execution of the installation.
Parker is your single connection to leak-free innovation with faster assembly. We offer a comprehensive line of fittings, valves, and tubing in support of our customers in the water and beverage industry. Our solutions are designed to boost customer productivity and profitability while offering specific performance expectations.
Being the world's leader in push-to-connect fitting technology, our engineers designed LIQUIfit™ fittings. The LIQUIfit body is manufactured from a unique bio-based, high-performance polymer produced from renewable plants, to expand the use of non-fossil-based resources.
LIQUIfit™ features a stainless steel grab ring, bio-sourced nylon 11, EPDM D – seal, FDA compliant, NSF/ANSI 51 and NSF/ANSI 61, is silicone-free and 100% leak-tested in production. Date coding guarantees quality and traceability. The innovative sealing and gripping design dramatically reduce bacteria growth, giving 100% cleanliness.
LIQUIfit™ fittings offer an innovative alternative for water applications; no fluid contamination occurs and environmental protection is guaranteed.
Our TrueSeal Fittings are lightweight, field attachable and connect to tubing without the use of tools. These all-plastic push-to-connect fittings are manufactured from FDA compliant materials.
Thermoplastic fittings, valves, and tubing play an important role in the purveyance of water and many other media applications and will for many years to come. Paying attention to the details outlined in this brief overview will help you hone your application skills for every installation, no matter how complex or simple it may be. Reliable, long-term performance of your installation depends on your attention to the proper selection of connector fittings, valves, tubing and accessories relative to the project requirements. Your customer confidence levels are in direct proportion to the quality of your work. In Part 2, we will look more in-depth at the differences in the compatibility of different materials, as well as specific applications. Stay tuned!
Visit Parker’s water solutions website for all available system solutions.
Author, Gary Battenberg is a technical support and systems design specialist with the Fluid System Connectors Division of Parker Hannifin. He has 35 years of experience in the fields of domestic, commercial, industrial, high-purity and sterile water treatment processes. Battenberg has worked in the areas of sales, service, design, and manufacturing of water treatment systems and processes utilizing filtration, ion exchange, UV sterilization, reverse osmosis and ozone technologies.
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