How To Replace A Sight Glass On A Boiler

If you have metal working projects that need to be completed, now is the time to consider investing in the supplies that are needed to weld. Learn here.

How To Replace A Sight Glass On A Boiler

10 December 2015
 Categories: , Articles

If the sight glass, also called a boiler glass or gauge glass, on your temporary boiler becomes clouded due to etching or deposits, then you will need to replace the unit. Replacement is an easy process and only requires a few simple tools and protective gear. Below is what you will need and how to perform the replacement:

Tools and materials required

  • Replacement sight glass - You will need to purchase a new glass tube that matches the length and diameter of your boiler's mount, and the glass should also match or exceed the strength rating for your particular boiler.

  • Brass nuts - You may use the original nuts as long as they are in good condition with no signs of corrosion or damage.

  • Rubber grommets - Use new rubber grommets at each end of the tube; old grommets may crack, lose their flexibility and be unable to adequately seal the tube connections.

  • Brass washers - Purchase new, matching brass washers to serve as buffers between the tube and grommets.

  • Adjustable wrench - To avoid slipping and possible damage or injury, do not use a pair of pliers for this task.

  • Eye protection - Wear appropriate goggles or a face shield to guard your eyes from shattering glass.

  • Gloves - Leather gloves provide protection against burns or broken glass for your hands.

Step-by-step procedure

1. Remove the boiler from a pressurized state - Never attempt to replace the sight glass on your boiler while the unit is under pressure. Take down the boiler pressure following the appropriate procedures before beginning the replacement procedure.

2. Turn off sight glass water flow valves - To shut down the water flow into and through the sight glass, turn each water valve at the top and bottom of the sight glass in a clockwise direction; keep turning until the valves are fully seated, but do not apply excessive pressure to these valve handles in order to prevent damage.

3. Drain the water from the sight glass - Locate the drain cock at the bottom of the sight glass, and open the valve slowly by turning it counterclockwise. Be sure to wear gloves and keep your hands out of the way to prevent burns if the water is still hot. Once the drain cock is open, allow all the water to drain from the sight glass.

4. Loosen the sight glass nuts - After the water has drained from the sight glass, loosen the brass nuts located at each end of the tube by turning them counterclockwise. Keep a firm grip on the sight glass to prevent it from falling and breaking once the brass nuts are loosened completely.

5. Remove the tube, nuts, washers and grommets - When you have loosened the washers at both ends of the sight glass tube, slide the nuts onto the tube an inch or so away from each end. Next, lift up on the tube gently to unseat the bottom of the tube from the connector, then pull the bottom of the tube outward to remove it from the top connector. The grommets and brass washers should still be attached to the tube along with the nuts.

6. Inspect the connectors - Look inside the connectors to be sure the seats are clean and clear of any debris, such as rubber residue or water deposits. If there is any debris present, clean them out thoroughly with a brush and solvent suitable for use on brass.

7. Install the replacement sight glass - After ensuring the connectors are clean, you are ready to install the new glass tube and hardware. In order, slide the brass nuts down each end of the glass tube, then the brass washers, and finally, the rubber grommets. Next, insert the top end of the glass tube into the top connector, then push the bottom end into the tube and slide it downward.

Once the tube is in position, slide the grommets, washers and nuts along the tube toward each end, then use your hands to begin tightening the nuts on the connector threads. When you are unable to tighten them further, use the adjustable wrench to tighten them to a point just past "snug". Do not overtighten the nuts, or you will break the glass tube.

8. Restore service to the sight glass - After the tube has been installed and the nuts tightened, restore service by closing the drain cock and opening the water flow valves on each end of the sight glass. Be sure to check for leaks before pressurizing the boiler.