How to Assemble FK Series Medium-Pressure Tube Fittings

In this video, you will learn how to assemble Swagelok 1/2 in. medium pressure stainless steel FK tube fittings used in combination with either 316 stainless steel or 2507 Super Duplex tubing.

Be sure to wear appropriate personal protective equipment such as safety glasses.

Here are some things to keep in mind before you begin. First, determine whether you will install the FK fitting by turns or by torque. Next, determine whether you will preswage the fitting with the manual preswage tool. Preswaging is not always necessary, but can be advantageous in tight spaces. For more information on manual preswaging, see MS-02-472.

In addition to any preswaging tools you may need, you will also need the following tools: deburring tools, ultrafine non-chloride marking pen, and the Swagelok FK depth marking tool. For torque installation, you will need a calibrated torque wrench with a crow foot at a right angle to the handle, plus an additional open-ended wrench for holding the fitting body. For installation by turns, you will need two open-ended wrenches and a Swagelok medium-pressure gap inspection gauge.

Now we will demonstrate how to assemble the FK fitting. First, we will assemble the fitting by turns. One turn is required to adequately assemble the fitting thread.

Thread the pre-assembled cartridge, which includes nut, ferrules, and plastic arbor into the fitting body until finger tight. Remove the plastic arbor from the end of the nut.

Select tubing according to specifications. Squarely cut the tubing to length. Then, deburr both the ID and OD surfaces.

To ensure the tubing is fully bottomed on the shoulder inside of the fitting body, use the FK depth marking tool. Insert the tubing into the FK depth marking tool. Use the depth marking tool appropriate to the tube OD as shown in this chart. For 1/2 in. sizes, use MS-DMT-8FK0.

Mark the side of the tube end with an ultrafine non-chloride marking pen above the depth marking tool. Insert the tubing into the FK fitting body. Make sure the tubing rests firmly on the shoulder of the fitting body. Check the depth mark on the tube. If any portion of the depth mark on the tube can be seen above the fitting nut, the tube is not fully inserted into the fitting.

Use a non-chloride marking pen to apply rotational alignment marks in a line that extends along both the nut and fitting body. Tighten the nut one full turn. As the nut is tightened, the tube depth mark will emerge out of the end face of the nut. The two alignment marks should be in line after one turn.

Once you have assembled the fitting, use the Swagelok medium-pressure gap inspection gauge to ensure that the fitting has been tightened sufficiently. Position the gap inspection gauge next to the gap between the nut and body. If the gauge will not enter the gap, the fitting is sufficiently tightened. If the gauge will enter the gap, additional tightening is required.

Now we will demonstrate how to install the FK fitting by torque. Thread the pre-assembled cartridge, which includes nut, ferrules, and plastic arbor into the fitting body until finger tight. Remove the plastic arbor from the end of the nut.

Select tubing according to specifications. Squarely cut the tubing to length. Then, deburr both the ID and OD surfaces.

To ensure that the tubing will be fully bottomed on the shoulder inside of the fitting body, use the FK depth marking tool appropriate for the tube OD. For 1/2 in., use MS-DMT-8FKO.

Insert the tubing into the FK depth marking tool and mark the side of the tube end with an ultrafine non-chloride marking pen above the depth marking tool. Insert the tubing into the FK fitting body. Make sure the tubing rests firmly on the shoulder of the fitting body. Check the depth mark on the tube. If any portion of the depth mark on the tube can be seen above the fitting nut, the tube is not fully inserted into the fitting.

Use a calibrated torque wrench with a crow foot at a right angle to tighten the nut. If you are not using a vise, use an open-ended backup wrench to hold the body steady. Tighten the nut to the specified torque. For the 1/2 in. fitting, tighten the nut to 110 foot-pounds or 115 Newton meters.

Use a non-chloride marking pen to apply rotational alignment marks and a line that extends along both the nut and fitting body. As the nut is tightened, the tube depth mark will emerge out of the end face of the nut.

Check the rotational alignment marks after assembly by torque. The specified torque should have caused the nut to turn approximately one turn. The two alignment marks should be reasonably in line.

Once you have assembled the fitting, use the Swagelok medium-pressure gap inspection gauge to ensure that the fitting has been tightened sufficiently. Position the gap inspection gauge next to the gap between the nut and body. If the gauge will not enter the gap, the fitting is sufficiently tightened. If the gauge will enter the gap, additional tightening is required.

For information on assembling other fitting sizes and materials, refer to these instructions. For 1-inch fittings, see MS-CRD-0249. For 1/4-in. through 3/4-in. sizes, see MS-CRD-0096.

To learn more about these or any of our other products and services, contact your local Swagelok sales and service center.