Dunbar Water Sight Glass and
Pressure Testing the Dunbar Boiler
By
Bruce Wm. Anderson
Picture 1 Dunbar Water Sight Glass Assembly
Picture 2 Dunbar Water Sight Glass & Fittings
A Water Sight Glass (Picture 1) is on one end of the Boiler. The gage glass of the Water Sight Glass (Picture 2) is .471” OD, .315 ID, .078 wall thickness, and 6 inches long (1/2” TGR gage glass--- high-pressure). It is sealed on each end by a packing nut, a gage glass EPDM washer--- ½ inch from McMaster’s Carr that needs to be modified by sanding down its outside diameter on a mandrel to fit inside the packing nut, and a brass (.040” thick---original?) or stainless steel (.0185” thick) washer 1/2 " inside diameter by 11/16 " outside diameter (Pictures 3 & 4). See modern day Gage Glass Care and Use Directions below. Water can be added directly to the Boiler by removing the ¼ inch square pipe threaded brass plug on top of the Water Sight Glass and drained from the boiler by removing the ¼ inch square pipe threaded brass plug on the bottom of the Water Sight Glass (Pictures 1, 5, & 6). The highest working steam pressure allowed from this boiler is 30 pounds. It should be safety checked by first filling the boiler completely with water and then pressurized with air to 60 pounds before installation. The female fittings in both boiler ends for the Water Sight Glass and pipe fittings should be held parallel by the use of a ¼ inch steel pipe substitution for the Water Sight Glass and pipe fittings (Pictures 7 & 8 - Jig Made by John Mueller) to maintain the correct orientation of these pipe threads during this pressure test. This will minimize the deformation of the heads under pressure.