There are four common water level gauges: glass tube type, flat plate type, two-color water level gauge and low-position water level gauge.
1. Glass tube water level gauge
Glass tube water level gauge, nominal pressure generally does not exceed 1.6MPa, nominal diameter has two types of DN15 and DN20, the inner diameter of the glass tube should not be less than 8mm, thickness not less than 3mm.
Glass tube water level gauge is mainly composed of steam cock, water cock, glass tube, drain cock and connecting flange.
The height and change of water level in the boiler are displayed through the glass tube. The center line of the glass tube should be concentric with the center line of the steam and water cocks of the water level gauge to prevent the glass tube from breaking due to torsional stress. In order to prevent the glass tube from exploding and injuring people, in the water level gauge with steel ball, there is a marble in the cock, and the impact of steam and water explosion makes the marble automatically close the steam and water cocks. At the same time, a protective cover should also be installed. The protective cover is generally made of thicker heat-resistant tempered glass plate. If the protective cover is made of iron sheet, a 12~15mm wide gap should be opened on the front and rear walls of the cover in the direction of observing the water level, and its length should be larger than the length of the glass tube. The gap at the back is to allow light to enter for easy observation. Do not use ordinary glass as a protective cover to prevent the glass tube from breaking, which will increase the danger.
2. Double-sided glass plate water level gauge
The double-sided glass plate water level gauge is mainly composed of steam valve, water valve, pressure plate, glass plate, drain valve, drain pipe and flange. Its characteristic is that the glass tube is replaced by a flat glass plate. The inner surface of the glass plate usually has a triangular groove. The refraction of light in the groove makes the steam-water boundary very obvious. Due to the different refractive indices of steam and water, steam and water will show different colors. Steam is bright white and water is gray. The boundary between the two is very obvious and easy to observe.
When the working pressure of the boiler is high, mica sheets can be embedded behind the glass plate to improve operating safety and extend the service life.
3. Two-color water level gauge
Two-color water level gauges are mainly of transmission type, reflection type and reverse transmission type.
1). Transmission type two-color water level gauge This water level gauge is composed of reflectors, light sources, red and green filters, cylindrical condensers, plane mirrors, screens, frames, and soda cocks.
The working principle of the transmission type two-color water level gauge is basically the same as that of other forms of water level gauges. The difference is that the light of the light source is reflected by the reflector and passes through the optical system, so that the part of the light that passes through the water appears green on the screen mirror, and the part of the light that passes through the steam appears red on the screen mirror, thus showing the change of the water level in the drum representing water green and steam red on the screen mirror.
2). Reflection type two-color water level gauge The reflection type two-color water level gauge uses the different refractive indices of light in water and steam. Through the reflection of the prism, the steam part of the water level gauge appears red and the water part appears green.
3). Reverse-transmission two-color water level gauge Its structure is between transmission and reflection. Its water level display uses both the transmission and reflection principles of light. The green light source is installed on the tongue of the meter. The red light source is installed on the left side of the meter. There are also color plates. After the light is transmitted and reflected, the water part of the water level gauge is green and the steam part is red.
4. Low-level water level gauge
According to regulations, when the water level gauge is higher than 6m from the operating surface, a low-level water level gauge should be installed.
There are two types of low-level water level gauges: liquid column differential pressure low-level water level gauge and mechanical low-level water level gauge.
The liquid column differential pressure low-level water level gauge is made by measuring the static pressure difference between two liquid columns using the principle of fluid static pressure. According to the different specific gravity of the liquid in the low-level water level gauge indicator, there are heavy liquid low-level water level gauges with a specific gravity greater than 1 and light liquid low-level water level gauges with a specific gravity less than 1. There are also differential pressure low-level water level gauges, etc.
The requirements for the working fluid used in the low-level water level gauge are as follows:
1. Insoluble in water.
2. Can be dyed into bright colors and can form a clear dividing line with water.
3. High boiling point and no corrosion.
4. Viscosity should be as small as possible.
The heavy liquids that can meet the above requirements include carbon tetrachloride (ρ=1623kg/m3), chloroform (ρ=1489kg/m3, bromoform (ρ=2890 kg/m3), etc. or a mixture of other solutions. The commonly used heavy liquid density is 1600~2000 kg/m3. In order to facilitate the observation of the water level, soluble dyes can be added: such as adding 0.01% croton red, the heavy liquid can be bright red. Light liquid is generally mixed with engine oil, kerosene and gasoline in different proportions. And adding an appropriate amount of phenolphthalein can make the light liquid red. The commonly used light liquid density is 700~800 kg/m3.