Gauge glass

Circffiation and heat transfer in this type of evaporator are strongly affected by the liquid level. Highest heat-transfer coefficients are achieved when the level, as indicated by an external gauge glass, is only about halfway up the tubes. Shght reductions in level below the optimum result in incomplete wetting of the tube walls with a consequent increased tendency to foul and a rapid reduction in capacity. When this type of evaporator is used with a liquid that can deposit salt or scale, it is customary to operate with the liquid level appreciably higher than the optimum and usually appreciably above the top tube sheet. 

Gauge glass and level instruments to be located at inlet-outlet end. 

For gauge glasses, it is good to have a vent at the top as well as a drain at the bottom. These should be inline for straight-through cleaning. 

Gas or electric driven pump. Verify adequate circulation by shutting off the glycol discharge from the absorber and timing the fill rate in the gauge glass. 

Be extremely cautious and do not install light weight gauge glass liquid level columns. Rather use the heavier shatterproof style. 

In many cases it is inconvenient to use a dipstick, due to the position or location of the tank, and there are a variety of direct and remote contents gauges available, including gauge glasses, float and weight, float and swing arm, float and indicator, hydrostatic, electrical capacitance, etc. 

Water column gauge glass and gauge cocks (try cocks)... 

Blowdown is generally provided only for a few seconds, or sufficient to drop the water level in the gauge glass by perhaps 1/2 inch (1.25 cm). Where 10 seconds ofBD is required, it is much preferable to stagger this over a period of time rather than all at once. 

The gauge cocks provide a backup means to determine water levels. In general, three gauge cocks (globe valve type) are vertically installed at spaced intervals, close to the visible gauge glass. 

Silica can also etch gauge glass, thus making it difficult to observe the water level. As a result, special flat gauge glass is used for boilers operating at over 250 psig. 

A type of glass used for gauge glasses operating at over 250 psig. Flocculant ... 

Make sure items such as gauge glasses, level controls, or pressure taps do not receive an impact head from an incoming stream. 

The liquid levels of products that have a Reid vapor pressure of 40 lb or more are generally determined by the use of gauge glasses, rotary or slip-tube gauges, tapes and bobs through pressure locks, or other types of gauging equipment. The type of gauging equipment depends on the size and type of the pressure tank. 

What is the difference between a gauge glass and a level glass Simple There is no such thing as a level glass. The liquid level shown in a... 

This discrepancy between the apparent level, in the gauge glass, and the actual level (see Fig. 6.1), in the tower, also occurs in any other type of level-measuring device. This includes external float chambers, kidneys, displacement chambers, and level-trols. The one exception to this is level-measuring devices using radiation techniques. 

Ambient-heat loss from the external gauge glass or level-trol... 

The gauge glass will normally be somewhat colder than the process vessel as a result of ambient-heat losses (an exception to this would be a refrigerated process). For every 100°F decrease in the gauge-glass temperature or level-trol temperature, the specific gravity of the liquid in the glass increases by 5%. This rule of thumb is typical for hydrocarbons only. Aqueous (water-based) fluids are totally different. 

For example, suppose the height of liquid in a gauge glass is 4 ft between the level taps. The glass temperature is 60°F. The tower temperature is 560°F. How much higher is the height of liquid in the tower than in the glass (answer 1 ft). 

This means that the liquid in the gauge glass is 25% more dense than the liquid in the tower bottom. 

Assuming a linear relationship between density and volume, the level of liquid in the tower above the bottom tap of the gauge glass must be... 

Once the actual liquid level inside the tower bottom rises above the top-level tap, no further increase in level can be observed in the gauge glass. 

The two gauge glasses shown in Fig. 6.4 both show a liquid level. Many of you may have observed this on a process vessel. We certainly cannot... 

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