S = SIZE ... what diameter is required…keep in mind hose size is normally expressed using the inside diameter (ID) or Bore. On certain applications the outside diameter of the hose can be of importance dependant on the type of fittings used.

T = TEMPERATURE ... In order to select the correct hose material it is important that you know the maximum and minimum temperature of the environment in which the hose has to operate, as well as the maximum and minimum temperature of the media being conveyed through the inside of the hose.

A = APPLICATION ... how and where is the hose going to be used, consider not only what the application is but the surrounding environment, number of hours used, are there any chemicals or petroleum products that the hose will come into contact with, what are the flexing characteristics of the application?

M = MEDIA ... What is the media being conveyed through the hoses? Is it abrasive. Is it laden with chemicals or fumes that call for greater chemical resistance in the polymer? Is the hose being used for more than one media ?

P = PRESSURE ... Establish what the working pressure is…positive (PSI)/Bar or negative (In. Hg)/mm Hg. Is the pressure constant or subject to surges in pressure.

Many rubber compounds contain a variety of ingredients, some of which may burn, a crude method of establishing the type of rubber compound is by means of a burn test and therefore the following information should be used as a general guide only.

Natural Rubber-NR: Pure rubber burns but has no characteristic smell. Compounds of natural rubber often have a recognizable odour. After extinguishing the flame, the surface is usually tacky.

Styrene butadine rubber - SBR: This burns with a black smoky flame and leaves a dry black surface after being extinguished.

Chloroprene rubber ( Neoprene,Baypren) - CR: This elastomer burns in a flame but will not support combustion. In other words, when removed from the flame, it is self-extinguishing. When burning, it gives a green tint to the flame. Be careful, because PVC, PVC/Nitrile, and Hypalon also have similar burning characteristics.

Acrylnitrile butadiene rubber ( Nitrile ) - NBR: Trade names include:
"Buna-N." This burns with a characteristic smell which leaves a nasty taste in the mouth. Somewhat similar to burning fat.

Butyl - IIR / Ethylene propylene rubber - EPDM: These burn with a yellowish flame similar to a candle.

Crush-recoverable or wire reinforced

There are two basic types of vehicle exhaust hose in general use today.

Crush-recoverable garage exhaust hose has no wire reinforcement, it is designed to be run over by vehicles and bounce back into shape.

The other style of vehicle exhaust hose that is used generally on overhead reels has a wire reinforcement. The wire support ensures the hose remains open at all times, even when it is partially coiled on the reel. These products should be used in conjunction with a powered exhaust extraction system and a suitable tailpipe adaptor. We also recommend that tight bends are avoided in the flexible exhaust hose in order to prevent a heat build up.

Simply put, PTFE (polytetrafluoroethylene) is a problem solver. When application parameters are outside the limits of many hose types, PTFE hoses made from Teleflex can be your best solution.

The chemical compatibility of PTFE, combined with its unique physical characteristics, make it the ideal engineered plastic for use in hose applications throughout the world. Consider the benefits:

Flexible and Strong
Combined with metal braid, Teleflex PTFE hoses can perform well under conditions where high pressures and continuous flexing and vibration makes this type of application a particular challenge. Properly applied and installed, braided PTFE hoses can withstand hundreds of thousands of flex cycles without fatigue or failure.

Chemically Resistant and Inert
Teleflex PTFE hoses can handle an almost endless variety of fluids at extreme pressures and temperatures. It is the most universal hose known.

Wide Ranging Temperature
Hoses made of PTFE can typically withstand temperatures from -100°F to +500°F (-73°C to +260°C) under most operating conditions. Even 350°F steam/cold water cycling can usually be handled safely.

Non-Stick, Low Friction
Almost no substance can adhere to PTFE. This property insures the purity of any fluid being transferred within this type of hose. It also allows for repeated reuse or alternate use with different fluids. With a coefficient of friction as low as 0.05, deposits cannot build up and flow rates are high throughout the hose assembly life.

Resistant to Moisture
By nature, PTFE lacks affinity to moisture. Absorption is less than 0.01%. In addition, no odor, taste or color is added to the transfer fluid by PTFE, making it an FDA approved material for food contact.

Ageless
Weather, exposure, or time does not affect a properly installed hose assembly. Teleflex PTFE hoses have an almost limitless shelf life.

Dash size is the common method used to refer to the inside diameter of a hose. Originally developed as a means of calling out size in a part number, this procedure indicates the size by a two digit number representing the relative ID in sixteenths of an inch.

For example, a quarter inch (1/4") hose in true bore is designated as -05 which has a 1/4" ID, in dash size a number of -04 would be designated which has a 3/16" ID.

However, dash sizes do not correspond to the exact hose inside dimension. Actual ID’s are smaller. This may be because rubber hoses are built to pipe sizes.

If exact inside diameters are required, ask for true bore sizes. Actual inside diameters are about one sixteenth of an inch less (but not in all sizes). They will still be called out by dash number. The following table lists the common hose sizes in inches with corresponding dash numbers for standard and true bore diameters.

Effusion or permeation is the process of migration of one substance into and through another. Usually the movement of a gas into and through a hose material. The rate of permeation is specific to the substance, temperature, pressure and the material being permeated. (Also refer to FAQ #8 regarding .040 wall versus .030 wall.)

Effusion can occur with many types of media, and with many different hose materials. In every case, certain questions must to be asked:

1. What is the rate of effusion? Is it constant or intermittent?
2. How hazardous is the medium being conveyed? Is it noxious? Is it poisonous? Is it flammable? Is it explosive? Is it corrosive?
3. What is the external environment? Will the product be exposed to sunlight? An open area? An enclosed space? Close to a source of heat or ignition? Near potable water sources or where it can create other health risks?
   

It is best to categorize the application based on the answers to the questions listed above. Usually you will find some general categories of concern. They are:

• Media that is not corrosive or noxious but may displace breathable air in an enclosed space thus creating a hazard to personnel.
• Media that will effuse at "vapor phase" if a certain temperature is reached, i.e. a fluid that boils at 125°F at atmospheric pressure. Such substances may form chemicals with exposure to air. These chemicals can be corrosive and/or cause injury to personnel or in some way create a hazard. For example, liquid chlorine can effuse as a gas and form hydrochloric acid in the atmosphere.
• Corrosive, hazardous or noxious media that is already a gas at atmospheric pressure and at ambient temperature and known to effuse through PTFE.
• Flammable or explosive media that may or does effuse under conditions within the scope of the application. Here again, no attempt is being made to cover all possible scenarios.

Tape wrapped convoluted hose is the method of producing convoluted or corrugated hose by progressive layers of material that are subsequently helically convoluted and sintered. The result is a highly flexible PTFE hose that can be produced in large diameters (up to 4") and in relatively long lengths.

Across almost every industry, applications for Teleflex PTFE hoses can be found. From caustic chemical transfer, to high purity food handling, to pharmaceutical processing, from aerospace and automotive to petrochemical processing...here are just some of the benefits:

• Reduced Maintenance Costs - Teleflex PTFE hose assembly life is often many times that of rubber or elastomeric hose. Per hour cost is lower.
• Less Production Loss - The real cost of a failed hose is often the loss of production or product spoilage incurred. The properties of Teleflex PTFE hose assemblies keep the assembly in service longer than other hose type.
• Greater Margin of Safety - Teleflex PTFE hoses handle even the most dangerous fluids...steam, acids, caustics, noxious gases, even flammable liquids, safely. Constructed with built in safety features, it is engineered not only for the application but also for the operator.
• Lower Inventory Costs - Teleflex hoses are designed to suit many different applications within a facility. Combined with longer service life, fewer inventory items to purchase and track, and designed for greater performance, Teleflex hoses save you money.

Innercore is made conductive by adding carbon to a small percentage of the innermost tube wall. The amount used and the way that it is introduced into the PTFE resin, provides sufficient conductivity without contaminating or coloring the medium.

Most Teleflex hose products are available with conductive and non-conductive liner. Conductive liner is required when the possibility of electrostatic discharge exists. Most applications do not require conductive hose liner, however, under certain conditions where build up of static electricity exists (usually produced by high velocity), conductive liner must be used to avoid a hazard.

This condition exists or is created when two different materials are in contact and electrons from one material move across its boundary and associate with the other material aligning themselves with that material. If the two materials are good conductors of electricity, the flow of electrons will remain balanced. If one or both are insulators (poor conductors of electricity) this flow will not occur. Instead, a charge will build up (phase separation) on one of the materials. When this charge exceeds the dielectric strength of the material, dielectric breakdown occurs.

In PTFE hose applications, consideration must be given to fluids and gases which are poor conductors. The flow rates of these materials must also be considered. For a liquid or gas to be considered a poor conductor of electricity, it will satisfy one or both of the following:

• The fluid is non-polar; there is an imbalance between protons and electrons.
• The fluid contains an immiscible component or a suspended solid; i.e. water in kerosene.
  

When such a fluid is conveyed in non-conductive PTFE hose, phase separation occurs and an electric charge builds up. The rate of build-up becomes a function of flow rate. When the dielectric strength of the PTFE is exceeded, a sudden discharge occurs through the tube wall. What occurs is essentially a small lightning bolt moving through the hose wall to a grounding point, usually the braid. The tube wall is mechanically and thermally damaged, leaving a pinhole or larger. The results of such a hazard range from hose failure, fire, explosion, personal injury or even death.

In hydraulics, high pressure often accompanies high velocity. Also in many applications, fluids are filtered somewhere in the system. Paper or glass fiber filter elements tend to "charge" the fluids they filter.

An area of concern regarding fluids are fuels. Fuels are usually non-conductive, having an electrical resistivity as high as 108 ohms. Examples include gasoline and white spirits, hydrazine, benzene, diesel oil, etc. Generally these fluids are transferred at low velocities but the potential still exists for an electrostatic discharge due to external environmental factors such as humidity and sometimes temperature. Even at fluid velocities lower than 1 meter/second, all these factors should be considered.

Note: The information stated here and elsewhere in this web site is not intended to cover all situations where electrostatic discharge hazard may exist. In all applications using fuel, steam or other fluids in this category.

In reality, neither one is better than the other. What counts is whether an assembly performs to accepted industry standards. Qualified aerospace and industrial hose assemblies utilize both attachment methods successfully. Even PTFE hoses which have a smaller window of correct compression than rubber and thermoplastic hoses utilize both methods. With regard to the cost of tooling, complexity of procedure, and time consumed, crimping has proved to be superior and is being used more.

Not necessarily. Tube wall thickness can change some of the physical properties of a hose. For example, it can increase the bend radius, reduce flexibility, and increase hoop strength. It should be noted that wall thickness does not appreciably change the permeation rate or "effusive" characteristics of PTFE. Permeation is a function of the relative porosity of PTFE which essentially does not change with thickness, the characteristics of the medium being conveyed, the pressure or other related factors.