INSTALLATION OF GAUGE GLASSES
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Sketch 1
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Notwithstanding the capability of Moncrieff Glasses to resist high pressure and sudden variations of temperatures, and their reputation to resist breakage, when breakage does occur, it is almost invariably the result of incorrect alignment or poor packing methods.
These sketches show the correct method of installing gauge glasses.
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Sketch 2
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Alignment
Tipping the glass to the right or left, or backward or forward, will bring the glass in contact with the metal parts supporting it, thereby causing a breakage within a brief period. Although the rubber washer at the top and bottom of the glass might temporarily prevent the glass from touching the gland or nut; after being subjected to the rigors of service, the washer becomes displaced and allows the glass to bear against these metal parts. It is important that the boiler be properly tapped so the water gauge is in alignment and the glass in alignment when inserted. Sketches 1 and 2 show the correct way and if followed, assure proper installation. Be sure that the nuts, holding the glass, are true to each other; that the top cock is screwed into the boiler the same distance as the bottom cock; that the holes in the boiler are perfectly aligned.
Dimensions
Glass should not be too long. (A) represents the top and bottom of the glass. Longer glasses provide greater opportunity for the steam end to be worn thin and eventually broken down. If boiler is tapped 9", center to center of hole, the gauge glass should be approximately 7" long.
Glasses should be of the correct diameter to slip easily into the glands. If too tight, the normal expansion is interfered with and unequal expansion occurs.
Packing
The rubber washers (B) used at the top and bottom should be of the highest quality (Jenkins Gauge Glass Washers are recommended). The washers should fit easily into the nut without being forced in with hammer or other tool. Do not use a wrench when turning down these nuts; hand-tight is sufficient and allows for normal expansion. A slight leak at first will cease when full steam is turned. Poor quality washers lose their resiliency very quickly and soon permit steam to escape. This rapidly increases until the entire washer blows out or sufficient steam escapes to set up violent vibration and unequal expansion.
Page 209
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