Since the advent of the semi-automatic water conditioning control valve followed by the automatic control valve, a common weakness has been the brine tubing connections between the brine valve and the brine tank. This circuit functions in two ways and is exposed to both a vacuum during the brine draw cycle and water pressure during a refill. A loose-fitting at either of these locations would cause loss of vacuum and/or a water leak, neither of which is acceptable and the result is often an unscheduled service call.
Brine is drawn from the brine tank when the control valve cycles to provide motive flow and pressure to the injector assembly (venturi) in the control valve while simultaneously opening the drain line to allow displacement of the accumulated hardness and metals from the resin bed during the service run. An injector consists of a nozzle and throat. The injector is selected based on the size of the media tank square foot (ft2) surface area. A venturi combines a narrow tube called a nozzle that restricts the flow of water which increases the velocity and decreases the pressure of the water passing through it, creating a partial vacuum immediately after leaving the nozzle. As water passes through the injector nozzle, the high velocity creates a vacuum which draws the brine from the brine tank, mixing with the water as it enters the throat. The brine is mixed with the water to dilute the brine from 100% concentrated brine to a 30% concentration. This diluted brine is introduced into the resin bed where it releases the calcium and magnesium from the resin and flushes it to drain. Maintaining the proper mixture is very important to ensure optimal regeneration. If the brine draw is weak due to poor vacuum, the brine is diluted below 30% and the result is a partial regeneration and potential salty water to service after the regeneration cycle is complete. Further evidence of poor connections includes overflowing brine tank, where a complete loss of vacuum won’t permit brine draw. However, the brine refill cycle will add additional water to the brine tank which could result in an overflow condition. Different manufacturers offered what they thought was the best connector based on what was available at the time. Let’s look at some of the options that were available.
Brass compression-style fittings were the most common and have been used for decades. In the early days, some valve manufacturers molded the 3/8” compression connection directly into the brass valve body produced at the foundry. The nuts, sleeves and tube supports were shipped with the valve to the assembler or were included with fully assembled softener/brine tank or cabinet style softeners. The brass compression-style connections are trusted for their dependable performance in virtually all conditions where temperatures range between 350 – 1200 F for domestic tap water applications. They also work very well for hot water softener applications where water temperatures can reach 1800 F. Attention to proper assembly is important because of the use of soft polyethylene or polypropylene tubing. Tube support is required to prevent distortion of the plastic tubing which guarantees effective gripping and a robust seal.
The connection is made by sliding the nut and sleeve onto the tubing, inserting the tube support into the plastic tube, inserting the tubing into the fitting until it’s bottomed on the seat, then tightening the nut until finger tight. The nut is then wrench-tightened with a specific number of wrench turns dictated by the specific fitting type and the size of the tubing. Based on their highly specific assembly instructions and the multiple components involved, brass compression-style fittings not only take time to assemble – around 40 seconds per connection – are labor-intensive - but also run the risk of being assembled incorrectly. For this reason, assemblers require some level of expertise when using this fitting type.
While brass compression fittings are viewed as highly dependable joint connections, with sealing performance that is second to none, higher labor costs are forcing manufacturers and assemblers to look for more cost-effective and less labor-intensive connection options.
Thermoplastic compression fittings
Plastic compression fittings have been used for over 40 years and vary in style and material composition. As with the brass compression-style fittings, tube support must be used with soft tubing. Plastic compression fittings are corrosion resistant and simple to install. The advantage is that there is no need to disassemble the fitting because all that is required is to cut the tubing square, insert tube support, insert into the fitting and hand tighten the ferrule nut to seal the connection. There is however a distinct disadvantage with these plastic fittings. They are prone to becoming loose with ambient temperature changes that coincide with seasonal weather patterns. Historically, it is necessary to retighten these plastic fittings to prevent the vacuum and water leaks previously mentioned.
Plastic Hose Barb Fittings
Plastic hose barb fittings are corrosion resistant and are not generally used for the brine valve connections. Typically, vinyl or polyurethane tubing or rubber hose is used with a hose clamp to ensure maximum grip and sealing power. Because vinyl or polyurethane or rubber hose is soft, it is subject to collapse during the vacuum phase of the brine draw cycle. Polyethylene tubing is not recommended because it will crack and leak.
Push-to-Connect (PTC) plastic fittings for water service have been available since the mid-1980s. There are many companies that offer competitive products. Many of those products require a locking clip where a vacuum service is required to prevent the collet from retracting which allows the entrance of air. To combat this problem, some competitive products use a double “O”- Ring seal to solve vacuum-loss. The double “O”- Ring makes it harder to insert the tubing and unless full insertion depth is achieved by engaging both “O”- Rings, connection failure may result. Additionally, debris entrapment between the “O” – Rings may promote bacterial growth in the fluid stream. The problem of collet retraction may persist during vacuum service and therefore, a clocking clip may be required to prevent seal loss during vacuum.
Parker LIQUIfit fittings and one-piece cartridges feature a D-Seal that maintains a bubble-tight seal around the tubing to prevent liquid by-pass. The stainless-steel grab ring is fixed to the cartridge body which prevents the tubing from “pumping” or retracting during vacuum up to 28 inches of mercury (Hg) at room temperature without the need of a retaining clip.
The compact cartridge design allows machining or molding of a cavity for the cartridge which enables automation of manufacturing processes, reduces the labor cost of assembly, reduces leak paths, and gives your product or equipment a new, clean profile. By eliminating the need for threaded connections, tube connections are made quick and easy without the need or use of tools.
With Parker LIQUIfit, gone are virtually all labor costs associated with compression-style fittings and assembly time can be reduced by as much as 90%. Seasonal retightening of the plastic compression nuts due to temperature variations is no longer a concern. Hose clamps are no longer needed when using polyethylene tubing, and locking clips aren’t necessary to prevent retracting collets. LIQUIfit fittings and one-piece cartridges solve the challenges associated with other styles of brine tube connections and improve the integrity and reliability of your component, product, or system.
Post contributed by Gary Battenberg, 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.
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