It may seem like a simple process, but choosing a pneumatic hose or tube can make the difference between a well-oiled machine and hours of maintenance. Here are 4 items to consider when choosing a pneumatic hose.
Working Pressure (W.P.)
The first item to consider when choosing a pneumatic hose is the working pressure of the system (obviously). Most hoses and tubes will have a label printed on the product wall, which will provide the working pressure and other important information. You want to choose a hose that will handle the normal pressure of the system, including any potential for over-pressurization, such as a loaded cylinder or external force. DO NOT rate the hose based on the compressor rating; you need to assess the system as a whole.
Large diameter hoses may have different working pressures than small diameter hoses, so don’t assume that a 1” hose has the same rating as a ½” hose. The large diameter hose has more surface area than a small diameter hose, which means the force on that hose is greater (Pressure x Area = Force). Take a close look at the working pressure of the hose and make sure it is properly rated for your application.
You also need to be aware that certain hoses are rated for vacuum and others are not. Designing a vacuum system with a normal pressure hose could result in the hose collapsing and cutting off the air flow in the system. A common mistake is using a low pressure hose on a compressor suction inlet instead of a vacuum rated hose. If the hose kinks or collapses in this arrangement, the hose could starve the compressor of air and cause major damage to the motor and pump.
The second item to consider when choosing a pneumatic hose is the minimum bending radius. All hoses and tubes should provide a minimum bending radius to prevent the hose from kinking. Kinks are especially problematic since they can damage the wall material and result in the hose failing prematurely. In addition, the kink is restricting the flow of air, making the system slower and less efficient.
In order to determine the system’s bending requirements, create a dimensional drawing and calculate the tube pathway. It may be tricky to predict the pathway before the system is built, but even estimated values are helpful in choosing a pneumatic hose. If you don’t feel confident in your system layout, choose a hose that can handle the radius smaller than the calculations to allow for any errors. In the case of an existing system, you can look at the existing tube ratings, or recalculate the radius based on the physical layout.
A good trick for close proximity bends is utilizing a fitting to do the bending while the hose provides the straight run. A simple elbow fitting out of a cylinder can alleviate a sharp bend that would normally require a highly flexible hose.
The third item to consider when choosing a pneumatic hose is temperature. This is especially prevalent in outdoor systems that may encounter low temperatures. Most materials will become very brittle at low temperatures and greatly decrease the pressure rating of the material, so read the hose temperature rating carefully before ordering.
The opposite is also true for high temperatures, such as engine rooms or a compressor outlet, where the material starts to melt or degrade from the heat. The hose manufacturer should provide information on the temperature rating and may even provide information on the pressure rating as the temperature changes across the rated range.
Even if the hose is rated for the correct temperature, frequently fluctuating temperatures could degrade the hose. The cooling and heating of the material could cause micro-fractures in the material, which grow over time and eventually cause the hose to fail. In these scenarios, you should establish a frequent inspection of the system to find potential failures and replace the suspect hose before a failure can occur.
The fourth item to consider when choosing a pneumatic hose is the makeup of the air. Most pneumatic systems use atmospheric air to supply the working media to a system, but not all atmospheric air is the same.
If your compressor is inside a facility that manufactures plastics or chemicals, the “atmospheric air” could contain cleaners, acids or aerosols that can eat away at the hose material. A filter would not necessarily remove these types of contaminants, so don’t assume your system is indestructible by sticking a big filter on it.
In other cases, the “atmospheric air” could contain particles or hardeners that would cause the hose to become rigid. You may be wondering why is that a problem? A rigid hose means that the hose cannot expand with pressure and will start to crack from the added stress.
In most facilities, the concentration of particulates are not high enough to affect the hose in the short-term, but it can be a factor in designing a long lasting system that can run for decades without maintenance.
If you would like more information about choosing a pneumatic hose or find a supplier who can provide you with that hose, feel free to contact us at RG Group and we’ll be glad to help you out!