It can be challenging to make sure you've covered all the bases during the tubing and hose selection process for medical instrumentation. For each application, there are many elements to consider, including chemicals, temperatures, pressures, and flexibility needs. The tips in this article are designed to help avoid situations in which the wrong tubing or hose is integrated. The article also presents critical details that can often be overlooked.
1. Check for Approved Ingredients
Know whether the tubing or hose must be constructed with the Food and Drug Administration (FDA) or other association-approved ingredients. If so, check the supplier's catalog or specification sheets for these approvals. Before proceeding, it is also important to determine whether the application calls for specifically approved ingredients.
2. Be Aware of Pressure or Vacuum Requirements
Some products must travel through the tubing or hose under pressure or by vacuum. Certain tubing materials cannot handle these situations, but reinforced hose often can. In fact, depending on the type of reinforcement (polyester braid, fabric, stainless steel wire, corrugation, convolution), certain types of hose are well suited for pressure applications, while others are better for vacuum.
3. Know the Temperatures Involved
It is important to know whether the tubing or hose being investigated can withstand the temperature of the product traveling through it, as well as the temperature of the environment it's in. Be aware of the temperatures operating within the tubing or hose as well as the temperatures surrounding it. And keep in mind that the higher the temperature, the less pressure the tubing or hose can handle.
4. Consider Flexibility and Resistance to Kinking
In some applications, the tubing or hose needs to bend around machinery. If so, products manufactured with characteristics to prevent kinking should be used. Similarly, for applications that involve repetitious movement, such as those dealing with robotics, the tubing or hose must be able to withstand this repeated flexing.
5. Look for Incompatible Ingredients or Substances
Product flowing through the tubing or hose may contain ingredients that could react with the tubing or hose material. In addition, the material of the tubing or hose may contain substances that could react with the product being conveyed. If an application involves transferring harsh chemicals, it is important to conduct any necessary research and to consult chemical compatibility charts to determine what tubing and hose materials can handle those chemicals. It is also important to note any other fluids and gases with which the tubing or hose may come in contact. Consider, for instance, cleaning products that may be used on the exterior or gases that may exist in the same room as the tubing or hose. The chemicals may seem harmless enough, but their effects on particular tubing and hose materials should be investigated.
6. Know Whether the Tubing or Hose Will Impart a Taste or Odor
Certain tubing and hose materials will, simply by their nature, not transfer a taste or odor. If an application involves items such as foods, beverages, laboratory fluids, or medicines, any taste or odor transferred to those items could be of concern. Also, some tubing and hose materials contain plasticizers to help them stay flexible. These plasticizers can occasionally leach out from the tubing or hose, thereby contaminating the product within. Other materials (silicone and polyurethane, for instance) are naturally flexible, so no plasticizer is needed. When selecting tubing or hose, be aware of these characteristics and how they can affect the product.
7. Determine Whether the Products Must Be Seen
In some applications, the user needs to see the flow of the product to check for consistency, progression, or to note measurements. Understanding the eventual application of the tubing or hose and whether products must be viewed as they run through it will affect hose choice. Depending on its material and construction, tubing and hose can be transparent, translucent, or opaque.
8. Learn Whether the Tubing or Hose Can Be Sterilized and Reused
Some applications require sterilization for reuse, so the tubing or hose must withstand sterilization with a chemical cleaning agent. These questions should be addressed: Can it be autoclaved? Does it simply flush clean? Can it withstand low-pressure steam sterilization or gamma irradiation? Knowing the answers to these questions could save money, so be sure to ask. And, depending on the labor and equipment involved to clean the tubing or hose, it may be less costly to simply replace it.
9. Consider Indoor or Outdoor Use
Note whether the application will require that the tubing or hose be used inside or outside. Conditions can vary greatly in either environment, but outdoor usage often has particular requirements. Tubing and hose that is used outside may need to resist a wider range of temperatures. It may need to handle the effects of rain, wind, and gases such as ozone. Sun exposure is another important consideration. Certain tubing materials and/or colors handle the effects of sunlight and UV better than others.
10. Be Aware of Moisture-Related Factors
Applications that involve water, condensation, or humidity have special considerations Tubing and hose materials react in different ways to moisture. Some materials will absorb water and other liquids, and that may be unacceptable. Absorption can cause the tubing to swell and can affect its physical properties. Certain materials like ether-based polyurethane resist attack from moisture and help inhibit mold growth.
11. Investigate Hardness and Softness Needs
Tubing hardness is measured as its durometer. Different scales, namely Shore A, Shore D, and Rockwell R, are commonly used for plastic and rubber materials. The lower the scale number, the softer and more flexible the material will be. For instance, a typical silicone tubing rating is Shore A50. Polyurethane tubing is not as soft as silicone and can measure between Shore A70 and A95. Harder materials like nylon and polyethylene are normally measured on the Shore D scale, and others (polypropylene, for example) use the Rockwell R scale. Flexibility and softness/hardness requirements differ greatly between applications, so the needs for a particular job must be carefully considered.
12. Check for Flammability
Depending on the type of material, tubing or hose can react differently if it catches on fire. Some might emit fumes, while others self-extinguish. Still others are nonflammable. Some tubing and hose, such as that made from particular polypropylene formulas, meets burn ratings established by Underwriters Laboratories (UL). Silicone tubing can self-extinguish. Fluoropolymer is nonflammable. But when tubing manufactured from the high-performance synthetic rubber Viton™ burns, hazardous chemicals can be released, and extreme caution should be taken.
13. Consider Quality
Some applications require that the tubing or hose transfer critical fluids. In some cases, there is reason to be concerned with the environmental conditions in which the tubing or hose is manufactured. In others, the application simply needs a drainage tube to transfer condensation from point A to point B. Applications vary greatly and the highest quality product available is not always a necessity. When the application is critical, it is important to research the tubing or hose under consideration to ensure it meets the required standards. When that's not the case, it may be possible to save money by using tubing or hose that doesn't meet such standards. Products discontinued by the manufacturer may be acceptable and available at a reduced cost.
14. Evaluate Surface Characteristics
Surface characteristics can also play a role in tubing selection. Questions to consider include: Does the tubing or hose need to have a mirror-smooth interior surface for efficient transfer with little to no friction? Will it transport granular materials, dry powder, or another substance where the surface condition is not a crucial matter? What about the outside? Should it be smooth, or does it need a surface texture like ribbing to make it easy to grip and hold on to? Surface properties can also affect electrical conductivity and static dissipation.
15. Consider Weight
Some single-layer tubing is very lightweight and a perfect match for applications where overall weight is a concern. Some hoses are multilayered and heavy. Add metal fittings and clamps to form an assembly, and that increases the weight. The overall weight of the tubing, hose, and/or assembly components used in an application needs to be considered. It is essential that the hose assembly's weight does not pull on other equipment.
16. Check for Abrasion Resistance
If the application involves rubbing of the tubing or hose against other equipment, it is critical that both the tubing or hose and, of course, the other equipment can withstand that abrasion. Certain tubing materials like polyurethane are better suited to abrasion resistance than others (silicone, for example). Corrosion resistance is another concern that is sometimes overlooked. Perhaps the liquid in the application is acidic. If so, it needs to flow through tubing or hose that can withstand it. Consider, too, the environment the tubing or hose will be in and whether corrosive fluids will come into contact with the tubing or hose.
17. Research Alternative Materials
Research each need individually to make sure the application is not being overengineered or that the tubing or hose is more than what is needed. Also consider coextrusions, which can save costs. Sometimes demanding performance characteristics required for the inside of a hose can differ from those needed on the outside. Hytrel®-lined PVC is one example — oil-resistant Hytrel makes up the interior while durable PVC protects the outside.
18. Know Packaging Requirements
Packaging should also be considered. It can dictate whether a 100-ft coil of tubing or hose acceptable or whether 20 straight pieces, each five feet long, is more appropriate. Consider whether it must it be bagged, double bagged for extra cleanliness, or boxed, or whether stacked coils on a wooden pallet are acceptable. Knowing how the tubing or hose will be used can help determine your packaging needs, allow for easier handling, and result in less waste. The product can be packed so that it's ready to use upon delivery.
19. Explore Custom Options
This can relate closely to packaging requirements. For instance, if the end use of the tubing or hose requires that it be cut into 6-in. pieces, why not have it delivered that way? Other customization can include special colors, heat-formed shapes, thermally bonded tubing, printing, coiling, molded components, or hose assemblies. Don't consider only stocked products — know the ultimate use of the tubing or hose to determine whether a custom product will save time and cost.
20. Don't Forget about Fittings and Clamps
In most cases, the tubing or hose must be attached to other equipment. Fittings and clamps come in many different materials — from nylon to PVDF, fluoropolymer to brass — so it is important to select the best match for the application. For some applications, a system can be built from one material (polypropylene, nylon, polyethylene, or fluoropolymer). Remember that the fitting's material must also be compatible with your application.
For any given medical application, it is important to consider everything from chemicals to flexibility when selecting the tubing. Applying the tips described above should help designers select the right tubing, avoiding situations that can lead to downtime add unnecessary cost.
This article was written by Alex Kakad, Product Manager for NewAge Industries, Southampton, PA. For more information, visit here .