Before inserting the tube in the coupling and tightening the nut on the ring, the ring must be precrimped on the tube. To do this we have a very practical tool called a “precrimping tool”
PRECRIMPING THE TUBE
The “precrimping tool” is shown in the figure
We will now use the following examples to illustrate the procedure. Firstly, we place the nut and the ring on the tube.
The tube must then be inserted in the precrimping tool. We ensure that it firmly abuts on the shoulder of the crimping tube and we hand tighten the nut. We maintain the body of the precrimping tool and tighten the nut almost two turns with a spanner.
And finally, we can:
- Unscrew the nut
- Remove the tube with the precrimped rings from the tools.
Once the tube has been precrimped we can insert our tube with its precrimped ring into the coupling we wish to connect.
Furthermore, it is essential for the integrity of the coupling that we do not apply excessive force when tightening the nut. If the connection is too tight, the olive will become distorted resulting in leaks.
Excessive tightening is the main cause of leaks in compression couplings.
As a general rule, a compression coupling must initially be hand tightened, then tightened a quarter turn with a spanner. The coupling must then be tested and if we observe a slight seepage, the coupling must be slowly tightened a little more until the seepage stops.
If during assembly and disassembly of these couplings you hear a squeaking noise when tightening with a spanner, it is too late, the coupling has been destroyed. The only solution is to replace it.
SEALING OF COUPLINGS
Here is a short reminder because, on worksites, I have already seen instrument technicians connect instruments to couplings without using Teflon. This is important because it can result in large measurement errors if there are leaks on the instrumentation couplings.
Here is the procedure to be followed to apply Teflon on all types of couplings:
The Teflon tape must be applied in the opposite direction to the
thread.
“Loctite” is now also used to replace Teflon but I would not recommend it because the couplings become difficult to remove.
