Industrial and laboratory OEM designers are constantly being challenged to come up with more versatile, user-friendly, light weight and cost-effective product solutions for their equipment and instrumentation. An important component in this design process is the selection of tubing connectors for the transfer and management of fluids and gases, particularly for mission-critical applications.
Although metal tubing connectors have been traditionally employed in industrial and laboratory markets, plastic connectors continue to supplant many that were previously metal, not only because of their increased options for design flexibility, improved ergonomics, reduced weight and lower cost, but also for their ability to effectively meet stringent industry standards in diverse and harsh environments. Many features of plastic connectors, which have been long proven in critical medical equipment design, are now being integrated into a broad spectrum of industrial equipment and laboratory instrumentation.
But choosing the right plastic connector can be a challenge. Plastic connectors offer more options for material selection, user interface and customized design than metal connectors. A basic understanding of the options available with plastic connectors will help the OEM to specify the most optimized features to achieve peak performance in the equipment or instrument being designed.
While plastic connectors effectively fill many roles, they may not be suitable for all laboratory and industrial uses. Brass, aluminum, die-cast zinc and stainless steel connectors are designed for extreme durability and high-performance fluid handling, particularly when influenced by high pressures and high temperatures. Choosing the most ideal connector first requires a careful assessment of the application. Following are the prime factors to be considered:
1. Temperature Range – the minimum and maximum temperature tolerances that the connectors will need to function within. Depending on connector material, temperature tolerances can range from -40° F to 200° F and above;
2. Pressure Range – determining the minimum, maximum and working pressures that the connectors will be expected to tolerate;
3. Flow Rate – assessing the required volume per minute, and the effect of fluid pulsation, and modulations from connect and disconnect forces;
4. Media – the viscosity, sensitivity and corrosiveness of the fluid or gas moving through the connection;
5. Exposure – degree of impact from external or internal conditions, such as UV, wind, dust, vibration, radiation, gases, water submersion, chemicals or cleaning agents, and mechanical stress;
6. Specialized Environments – for food and pharmaceutical grade manufacturing, including wash-down, cleanroom and aseptic environments, and vacuums;
7. User Interface – level of human contact expected with the system and connectors;
8. Cycle Life – anticipated maintenance and changeability required to be performed on the system, and expected longevity of the system in operation.
The requirements of the application will then determine what materials would be best suited for the connectors.
Plastic connector materials
The material chosen for plastic connectors should be based on the mechanical requirements of the connector and the type of media that will be moving through the system.
Significant pros and cons need to be weighed in the selection of connector material. Mechanical properties such as toughness, ductility, impact strength, transparency, lubricity, temperature capability, ozone resistance and UV compatibility need to assess when selecting the most functional material for the application.
A broad spectrum of plastic resins can be selected from to produce connectors, each with different characteristics to match the needs of system designers. These plastic resins are commonly used for producing connectors:
Polyethylene – chemically resistant, translucent or opaque thermoplastic with low temperature impact, which can withstand a variety of application environments;
Polycarbonate – hard, transparent thermoplastic with moderate chemical resistance. It provides good impact resistance and superior dimensional stability;
Polypropylene – soft thermoplastic that is highly resistant to chemical attack from solvents and chemicals in harsh environments;
Polyamide (Nylon) – versatile thermoplastic with good wear and chemical resistance, low permeability to gases and performs well at elevated temperatures;
ABS – tough thermoplastic with good stiffness and impact resistance even at lower temperatures, as well as good dimensional stability and high temperature resistance;
Acetal – strong and lightweight thermoplastic that provides high strength and rigidity over a wide range of temperatures;
PTFE – fluoropolymer resistant to most chemicals and solvents, with stability at high temperatures;
PVDF – thermoplastic that is mechanically strong with good ductility over a broad temperature range, as well as having excellent chemical resistance.
After the most appropriate material for the production of the connector is determined, the type of connection that best suits the laboratory or industrial need can be assessed.
Connectors are designed to accommodate tubing of varying hardness (durometer), from soft and flexible like PVC, silicone and C-flex®, to semi-rigid types like polypropylene, polyethylene, polyurethane and ethylene vinyl acetate (EVA).
To facilitate these varying styles of tubing and their respective application needs, different connector types are used, including barbed connectors, check valves, luer connectors, quick connects, threaded luers and tube-to-tube connectors. Of these, the most commonly used tubing connectors are tube to tube connectors, luers and quick connects. These basic connector styles can cover a wide range of liquid and air applications in laboratory and industrial environments.
*Tube to Tube Connectors
A popular choice for applications that do not require the disconnection of equipment or parts at any point during production or use. Tubing connectors are available in many different configurations, sizes and material options to adapt different tube sizes or styles, reroute the flow direction without kinking, and act as a manifold.
Delivery systems can employ conical or taper seal connectors, called luers, to link various system components. The male and female components of luer connectors join together to create secure, yet detachable, leak-proof connections with no o-ring or gasket required.
Quick connects (quick disconnects) allow flexible tubing and/or equipment to be quickly and safely connected and disconnected. They may be preferred over general connectors for fluid control because they can incorporate built-in shut-off valves that prevent spillage, allow multiple disconnections and faster servicing.
Plastic barb-style connectors provide designers with a capability to accommodate the widest possible range of tubing properties and application conditions, including a multitude of configurations such as tees, Ys, elbows and manifolds. A number of barb designs are available – each with unique characteristics to tailor connection performance to specific needs – for handling assembly forces, tensile resistance and blow-off resistance without the need for clamps.
Many factors can reduce the tubing’s ability to perform under pressure including temperature, chemical degradation, mechanical stress, fluid pulsation, selection of connector type and barb design. The latest generation of plastic connector technology affords designers and manufacturers with a wide latitude of flexibility to design and set-up applications that custom fit to their specific needs.
Compared to metal, plastic connectors provide a considerable reduction in weight, and much improved flexibility with regard to the equipment they serve. Uniquely equipped to do so, plastic quick connects allow rapid and easy servicing and maintenance of assembly line equipment, filling and packaging systems which limits system downtime and speeds throughput. Color-coding on plastic connectors also makes for quick tube identification and reconnection.
The cost difference between metal and plastic connectors is a major motivating factor pushing instrumentation, equipment and system designers to further embrace plastic connectors in laboratory and industrial applications.