It's your first day on the job in a new [to you] industry and you are faced with a large amount of information. Everyone is using terminology that you’ve never heard before and you are hit with a truckload of information. It can seem like you are drinking from a fire hose at this point. To help, we created this fittings 101 post to help you understand the basics. This is the first of two posts regarding the basics of what you absolutely must make sense of before you can move forward if you are new to the world of fittings.
First, we need to start at the very beginning -- what is a tube fitting? Unknown to most people, our world is filled with fittings. You would be hard-pressed to be somewhere where there is not a fitting within a few feet of where you are standing. So, with all these fittings around us, what are they doing?
A fitting is simply a manufactured piece that connects one component to another. For tube fittings specifically, they can connect:
one tube to another tube
a tube to a hose
a tube to a hydraulic component, such as a valve
These fittings have two major functions -- sealing under pressure and holding tube under pressure. The goal is to create a seamless transition from one piece to another. In an example using tubes, if you are trying to create a connection between a tube going one way and another tube going in a different direction, you would put a fitting between the two so that they are joined together as one.
Since we are primarily going to be talking about tube fittings, it’s important to understand one thing about tube terminology first. When talking about fitting sizes, it is always based on the tube OD (outside diameter). The size designation has nothing to do with dimensions on the fitting itself, only the tube OD that is intended to work with that fitting.
Figure 1: Tube and Tube OD
Now that we’ve established the importance of the tube OD, we can add a few more details to what a fitting size is. As stated before, the fitting size designates what tube OD should mate with the fitting. The term that is commonly used is “dash size”. A dash size is the tube OD multiplied by 16. i.e., if we start with a ½” OD tube, we multiply ½” x 16. This calculation tells us we would use a “-8” sized fitting for a ½” OD tube. You can also reverse that, and say 8 ÷ 16=1/2, therefore, a “-8” fitting goes with a ½” OD tube.
Note: Metric fittings use different nomenclature and does not follow any of the same rules. This explanation will require its own article.
Figure 2: Size 8 fitting
By nature, a tube fitting is a connector of one component to another. There are two types of connections or “ends” that can be called out on a tube fitting. First, is the tube end, which as the name implies is the end that attaches to a tube or hose. The other end type is the port end, which is intended for connecting into the pump, valve, cylinder, etc. The port end allows the fitting to act as a bridge between the tube and the component. A fitting that has both a port end and a tube/hose end is commonly referred to as an adapter. An example of this would be connecting the tube directly to a pump. There are several end configurations that are possible, and most fitting manufacturers will be able to supply any size or configuration you may need. See Parker’s tube fitting and hose adapter product lines.
Figure 3: Port and tube end fitting
There are many configurations that a fitting can have. For simplicity, these configurations can be put into two buckets -- straights and shapes. Straights are fittings that are straight in shape. Shapes could be describing a variety of configurations such as, 90-degree elbows, 45-degree elbows, tees (three ends) and crosses (four ends). As stated before, the ends of each fitting could be a range of styles and sizes, such as, all tube ends, one tube end with one port end, two tube ends with one port end, etc. Examples are shown in Figure 4.
Figure 4. Assortment of Fitting Configurations
As mentioned, this is the first of two posts that cover the first day of fittings basics. Now that we better understand the very basics of fittings, we can move into more specific terms and definitions in the next post. So, if you felt like you were drinking out of a fire hose, this should bring the water pressure down to maybe a hose from a small fire truck, and the next article should bring it down to maybe a standing a few feet away from a yard sprinkler.
If you have any questions or comments, please post them, and we will respond if warranted. To talk to our techConnect engineer team directly, they can be reached at Parker Tube Fittings Division, 614.279.7070. See Parker Tube Fittings Division's full line of tube fittings and hose adapters.
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Contributed by Emily Alexander, senior design engineer at Parker Tube Fittings Division
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