What do you think of when it comes to liquid chromatography composition? Pump, injector or detector? These are really critical, but there is another category of components that is often overlooked, and that is connections and piping. These components may seem inconspicuous, but they play a very critical role in the performance of the system. I will discuss these connectors with you in several articles, and I hope you can gain something!

What is a connector?

Dictionary Definition: A small part used to connect, adjust, or fit other components (as in a piping system).

In layman’s terms, a connector is a component used to connect, adjust or modify the pipeline. It is not only used for the connection of different modules, but also many connectors are used inside the same module.

Basic knowledge of connectors

The connector is usually composed of a nut and a ferrule (also known as a pressure ring or a blade ring, etc.), where the ferrule is a sealing component, and the nut is used to fix the ferrule.

What nut and ferrule to use will be determined primarily by these parameters:

● Thread to accept port

● Material of receiving port

● Receiving port geometry

● Size and type of piping used

● Expected pressure value

Screw nut

We usually distinguish different nuts based on some characteristics. For example, the head geometry of the nut, the material of the nut, and the thread of the nut. One of the most important features is the thread, which is the key to matching the nut and port.

The thread of the nut is usually external, but the thread of some nuts is internal. This kind of internally threaded nut is called an internal thread nut. Most of the external thread nuts used in the preparation of liquid phase are mainly used.

How do we describe or name the thread size of a nut?

10-32 is a common thread specification in higher pressure systems. Note that it is actually composed of two parts, separated by a hyphen in the middle. The front part indicates the diameter of the thread, the “10” here is the meaning of the American thread standard number 10, that is, 3/16 inch (4.7625mm), the rear part indicates the thread pitch, and “32” refers to the thread per inch The number of threads is 32 threads per inch.

Let’s look at another thread size 1/4-28 commonly used in low pressure systems, where “1/4” means the thread diameter is 1/4 inch (6.35mm), “28” and the previous “32” Again, it indicates the number of threads per inch.

The above two examples use imperial units, and some threads use metric units, which will be more intuitive, such as M6×1, which is relatively easy to understand. “6” means the thread diameter is 6mm. “1” means that the distance between adjacent threads is 1mm.

Thread diameter
Thread spacing

Now you should know the size of the thread!

Let’s do a little test, thread: 5/16-24

What is the diameter of this thread? What is the pitch?

(Note: the answer is at the end of this article)

Regarding the geometric shape of the nut, the common ones are knurled, hexagonal, square and wing-shaped, etc. For some hexagonal and square-shaped nuts, it needs to be tightened by a suitable wrench, and the knurled or winged shape can be directly tightened by hand.

The material of the nut

Nut materials can be divided into metal materials and polymer materials. Commonly used metal materials such as 316L stainless steel, Hastelloy and titanium alloys, and polymer materials such as PEEK, PTFE, PFA and PCTFE. The selection of specific materials can be considered from the aspects of chemical compatibility and compressive strength.

Other factors – nut length and channel size.

The length of the nut mainly depends on the installation position of the connector. Shorter nuts can be used in places with limited space, and long nuts can be used on angled ports to reduce the impact of disassembly and assembly of adjacent connectors (such as six-way valves). nut on is usually of different lengths).

The channel size of the nut is determined by the pipeline and needs to match the outer diameter of the pipeline, which is generally slightly larger than the outer diameter of the pipeline.

Card cover

We mentioned earlier that the ferrule is a sealing component, which achieves sealing by squeezing the outer wall of the pipeline. The ferrule is simpler than the nut. Let’s take a look at it together.

Assorted card sets

Factors to consider when selecting a ferrule are the size of the pipe, the pressure value, the matching nut and the geometry of the receiving port. The geometry of the receiving port is the most important. We need a narrower angle than the receptacle port for the ferrule to press against the line to generate enough pressure.

As mentioned above, nuts can be classified by “low pressure” and “high pressure”. The high and low here are relative, and the ferrule can also be divided into “low pressure” and “high pressure”. Usually, the low pressure port adopts a flat bottom configuration. The high pressure ones use a conical configuration.

Connections at higher pressures – “swaged” connections

Swaged refers to the permanent assembly of a ferrule on a pipe. This method is unique in high-pressure applications. Swaged connections are usually used on stainless steel connections and pipes, which will help the connection obtain better quality. Great pressure resistance. Of course, before swaging, it is necessary to confirm that the pipeline has been flushed with the bottom of the port, because swaging is an irreversible process, and once the swaging is completed, it is almost impossible to remove the ferrule.

Swaged in different sizes

Card sleeve material

Ferrules are usually made of materials such as stainless steel, PEEK, ETFE, PP and PCTFE. Materials like PEEK and stainless steel are commonly used to make ferrules for high pressure applications. Softer polymers, including ETFE and PP, are mainly used in low-voltage applications. It is also necessary to pay attention to the chemical compatibility of different ferrule materials.

Other factors

Achieving a good connection requires consideration not only of the effect of the connector, but also other factors, including the following:

Pipeline: Different materials will bring different pressure resistance and chemical compatibility (the specific content will be described in detail in the next article).

Receiving Port: The ferrule should match the shape of the port, and one very important rule to note is that the material of construction of the receiving port must be at least as hard as the material of construction of the pipe.

Any connector needs the nut and the ferrule to work together to fix the pipeline, but the connector divided into two parts is a little inconvenient to use, so the one-piece connector was introduced later, which is generally made of polymer material. , such as PEEK. This will be more convenient and simple to use.

PEEK integrated connector

Quiz Answers:

The diameter of the threads is 5/16 inch and the pitch is 24 threads per inch.

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