Slip-Locks as the name describes, slip together and lock. In the misting industry these fittings are made out of brass with nickel plating. The tubing used is high pressure nylon. The locking occurs under pressure. The greater the pressure the harder they lock.
We are not talking about the plastic slip-locks you can buy at the hardware store. Again, these are made out of brass to give them the strength to handle high pressures.
Slip-Locks have their place, typically not in industrial environment. If you are a home owner looking a patio mist cooling, YES, great application. Easy to pipe and hang, small form factor, tubing is flexible.
Keep the pressure below 1000 psi for safety sake. 500 psi is a great operating pressure that will produce a fine nozzle mist.
Slip-Locks can be used with plastic or nylon tubing. Nylon has a higher pressure rating and is a standard in misting industry. Nylon is a stronger material and has a thicker wall to give it that 1000 psi rating popular in misting.
There are two sizes of Slip-Locks available, 1/4" and 3/8". The 1/4 and 3/8" reference outside diameter (OD) of the tubing. Home application would use 1/4". 3/8" could be used if you have over 20, maybe 30 nozzles depending on nozzle orifice size.
As you would expect there are several different slip-lock fittings available. They consist of coupling union, unions with 10/24unc to connect a nozzle, Tees, Ells, Ends with 10/24unc.
Pictured below is the same fitting above but cut in half by a band saw.
In this cutaway there is a locking mechanism with barbs. The barbs push against and grabs the tubing as pressure increases. With no pressure the tubing can be sliped out for adjustment or replacement.
This has an advantage over compression fittings. Once a compression fitting is set and compressed the ferrules are locked in place and generally cannot be removed without damage to the ferrules.
Tubing should be cut with a tubing cutter, not with a hack saw or sawzall. The cut has to be clean with no burrs.
I suggest a light grit sanding of the outside edge of the cut, just a quick brush of the edge. Then place a very small amount of liquid soap or just some water on the outside end. This helps to easily slide the fittings together.
If you have a burr or are not using any lubricant there is a good chances you will not get the tube all the way into the fitting. You could possibly dislodge the rubber o-ring gasket and then the fitting will leak.
When you slip the two together you will notice the connection can be tight. As mentioned above using some sort of lubricant helps with the process.
Using water is a good first choice for a lubricant. A second and safe choice is to use a small amount of dish soap or Vaseline in small amounts. Just enough to coat the outside edge end where the tube was cut and clean up or debured.
All this does is help the tube slip under and pass buy the o-ring to obtain a seal and complete fit.
One other advantage is the ease of removal. A little Vaseline goes along way keeping that rubber o-ring seal lubricated. That is the whole purpose of this exercise, ease of install and remove.
Removing Tube from Fitting
When remove the tubing from the fitting, first make sure there is no water pressure in the tubing, then the collet sleeve must be pushed in towards the fitting body and held there. Then the tube can slide out.
This can be difficult depending on the tube/fitting positioning. Sometimes you have to work at it. Holding the collet in with enough pressure and pulling the tube out can be a chore.
Occasionally I will use a channel lock pliers to go around the tube but not crimp the tube and slide it up against the collet sleeve. This gives you the ability to put greater pressure on the sleeve to open up its jaws/barbs and release the tube.
Why only 1/4" and 3/8" fittings?
Pressure rating, As I said above, the tubing has to have a thick wall to withstand the pump pressure. As you get above 3/8" the wall thickness has to become quite thick to handle high pressures. It becomes a economics issue. Manufacturing and material costs become high. Is it worth it? Are there alternatives? Maybe copper or stainless steel tube.
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