How to properly tighten a fitting assembly into a port

A satisfying fluidic connection must be sufficiently tight to prevent any leakage, and the assembly must be seated correctly so that no pocket of liquid is created within the port (no creation of dead volume). We will take here the example of the tightening of a tubing piece into a Fluigent 2-SWITCH™ receiving port:

1. Cut the tubing to the appropriate length with a tubing-cutter, leaving a square-cut face.

 2. Slide the nut over the tubing with the nut thread facing the tubing end being connected.

 3. Slip the ferrule over the tubing, with the tapered nose of the ferrule facing either the nut (flat-bottom geometry) or the port (coned geometry).

4. Two cases:

a. The tubing OD is wider than the port hole diameter.

        • In this case, let a length of tubing extend after the ferrule and insert the assembly into the receiving port, making sure that the tubing goes to the bottom of the port. Then, maintain the tubing bottomed out in the port and tighten the nut finger tight.

      • If the fitting needs to be wrenched, tighten further with a wrench according to manufacturer’s instructions (keep holding the tubing).
      • To check the tightness of the connection, pull gently on the tubing. It must remain fitted in the ferrule and nut.

 

b. If the tubing OD is smaller than the port hole diameter,

      • The trick is to avoid inserting the tubing inside the port hole while bringing it near enough to avoid the formation of a dead volume with a pocket of liquid. To manage this, allow only a little length of tubing to come out of the ferrule or out of the sleeve if you are using one and insert and fasten finger-tight the assembly into the receiving port while maintaining the tubing in this position.

      • If you are using a sleeve, it should bottom out in the receiving port.
      • For adapters and unions, a plug can be screwed on the other side of the small tubing to act as a gauge and block the small tubing at the end of the port.
      • If the fitting needs to be wrenched tighten further with a wrench according to the manufacturer’s instructions (keep holding the tubing). To check the tightness of the connection, pull gently on the tubing. It must remain fitted in the ferrule and nut.

 

Coline Lemang, R&D Engineer  

The ability of the MFCSTM combined with the Flow-rate Control Module greatly enhanced our control of the flow rates.

Dr. Andrew Hudson,
Leicester University, UK

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