Removing and Replacing Windows

The windows in the Cryostation Base Platforms can be removed and replaced. Please consult the Windows Buyers Guide for selecting a proper window.


The vacuum window must be thick enough to safely support the vacuum differential across it. Use a Window Calculator to determine if the thickness of the window is enough to keep the integrity of the window.

When replacing the windows be aware of how the windows are positioned with respect to one another. Be sure when vacuum is pulled, the windows do not collide with each other or other components of the system.

Vacuum Housing Windows

Always remove the housing from the system first and lay on its side, so as not to damage the o-rings. To remove the black window covers twist the black cover counter-clockwise; the cover will come loose and can then be removed. To put the cover back on, align the four tabs on the cover with the four tabs in the delrin ring and gently twist clockwise.

Figure 1: Window housing removed and on its side

To remove the windows a window tool is used. The Montana Instruments accessory kit comes with the window tool(s) needed for your system. There are a few variations, as shown below. On the left in Figure 2 is a 30mm window tool for 30mm windows. In the center is the most commonly used window tool, which is for 50mm windows (this tool is used in the rest of the document). Lastly, on the right is the 50mm window tool that is hollowed out; this is used for castle systems, or mounting KF vacuum flanges in which the full 50mm diameter is needed.

Figure 2: Various window tools

Each window tool has four tabs that line up with the notches in the delrin retaining rings. Align the window tool with the notches in the delrin retaining ring and turn counter clockwise to remove the delrin ring, as shown in Figure 3. Sometimes the tool slips and this can damage the window, so be careful to not put too much force on the window tool when removing the delrin retaining ring.

Figure 3: Window removal tool

Next, remove the retaining ring. The user can now carefully remove the window. As seen in Figure 4, the window sits on an o-ring and there is enough room in the window slot for a window slightly larger than 50mm, so a 50.8mm window will fit in the space. When replacing the window, be sure that the window is centered over the o-ring and that the o-ring is free from debris. If the window slides down and the o-ring is not fully covered, there could be a vacuum leak. Also, try to carefully place the window over the o-ring and avoid having to re-position it, as that could spread L-grease into the clear aperture of the window.

Figure 4: Retaining ring removed, access to window

Radiation Shield Windows

The radiation shield windows are simply held in place by the spring fingers with some added N-grease. The windows unscrew from the radiation shield, as shown in Figure 5. The pitch is 1mm per rotation for reference.

Figure 5: Unscrewing radiation shield window

The window can be removed by pressing it out of the spring fingers (Figure 6). Make sure your gloves are clean before performing this step so the window will remain clean. The window can be quite tight, so some force is required.

Figure 6: Press window out

To add a new window, first add a very thin layer of N-grease on the edge of the spring fingers (Figure 7). This layer should be so thin that none of the grease spreads onto the optic.

Figure 7: Adding N-grease to spring fingers prior to mounting a window

After the grease is applied, the window can be replaced by press fitting the radiation window ring onto the window. The window should not be loose. The radiation window ring should hold the window evenly.

Figure 8: Replacing window in radiation window holder

Before placing the radiation window back in add a small amount of N-grease to the threads and then screw back in place.

Other Windows

For low working distance windows, it is typically not possible to replace the vacuum window without getting a new window since the window is epoxied in place. Either an aluminum blank or a custom vacuum window can be purchased from Montana Instruments.

For castle windows, or other windows, a custom window tool is generally provided. It can be more difficult to remove and align windows in a castle. A user with these options will get more information in a manual addendum for options.