204 Questions
EASY What is the purpose of a gauge glass in a boiler?
To continuously determine the boiler water level
According to ASME BPVC I Part PG-60.1, how many gauge glasses are required for boilers with a maximum allowable working pressure exceeding 400 psi?
Two
What is the minimum diameter of the unrestricted drain opening required for steam heating boilers?
1/4 in.
Why is it critical to know the boiler water level at all times?
To prevent accidents and ensure safe operation
What is the minimum distance required between the lowest visible water level in a gauge glass and the lowest permissible water level?
2 in.
What is an alternative to one of the required gauge glasses for boilers?
Two remote water level indicators
Which type of boiler requires a permanent indicator of the lowest permissible water level?
Heating boiler
What is the purpose of the valved fittings attached to the water column or boiler?
To facilitate cleaning
What is the simplest and least costly gauge glass design?
Tubular
What is the purpose of the stainless steel check ball in the lower valve on the gauge glass?
To stop the flow of fluid when the glass breaks
What determines the pressure ratings of gauge glass tubing?
All of the above
What is the minimum overlap required for adjoining sections of gauge glass assemblies?
1 in.
What is the purpose of the washer or packing ring and a nut at each end of the gauge glass tube?
To hold the gauge glass tube tightly in place
What is the minimum size of piping required for connecting a water column to a steam boiler?
NPS 1 (DN 25)
What is the purpose of the drain valve or cock on the lower gauge glass fitting?
To remove any solid material that may collect
What is the purpose of the metal rods or transparent shield surrounding the gauge glass?
To protect the gauge glass from breakage
What is the limitation of using tubular gauge glasses?
Low pressure and temperature
What is the requirement for installing multiple gauge glasses?
The visible portions of the gauge glasses must overlap
When inserting the gauge glass into the steam fitting, what should be done first?
Insert the gauge glass into the steam fitting first
Why should the operator wear a face shield when opening the valves?
To prevent injury from steam or water
What is the maximum pressure for which tubular gauge glasses are available?
3000 kPa
What type of gauge glass is used for pressures up to 70 000 kPa?
Armored-Type (Flat)
What is the purpose of the transparent mica coating on the inside surfaces of the glasses?
To prevent water from directly contacting the glass
What is the recommended method for tightening the bolts on the transparent gauge glass?
Starting at the centre and working outwards
What is the purpose of the reflex gauge?
To create a sharp line of demarcation at the liquid level
What is the first step in replacing the armored-type (flat) gauge glass?
Close the steam and water valves on the gauge glass and open the drain valve
Why should the surfaces of the gauge body and the bolted covers be polished perfectly smooth?
To prevent the gasket material from plugging the valves on the gauge
Why should the old gauge glasses not be reused?
Because they are no longer suitable for high temperature high-pressure service
What is the purpose of the drain valve in the installation shown in Figure 15?
To permit all the connections to be blown through
What is the purpose of the water column in the installation shown in Figure 16?
To dampen agitation in the water and trap sludge or sediment
What was the purpose of try cocks in the past?
To provide a means of point level detection when the gauge glass is being replaced
What is the minimum distance between the lowest visible water level in the gauge glass and the lowest permissible water level in a boiler, according to ASME BPVC I Part PG-60.1?
2 in.
What is the minimum distance between the lowest visible water level in the gauge glass and the lowest permissible water level in a horizontal firetube boiler with a diameter greater than 400 mm, according to ASME BPVC I Part PFT-47.1?
75 mm
What is the minimum distance between the lowest visible water level in the gauge glass and the lowest permissible water level in a steam heating boiler, according to ASME BPVC IV Part HG-603?
25 mm
What is the main reason for the failure of gauge glasses?
Corrosion caused by alkalinity and silica depletion at higher temperatures
What should be done first when a gauge glass fails?
Shut off the steam and water valves on the gauge
Why is it important to wear a face shield when replacing a gauge glass?
To protect against injury from fragments of glass
What should be applied to the washers when installing a new gauge glass?
Graphite
What should be installed on one side of the boiler?
New mica, new glass, and new cover and replace the nuts on the cover
How should the nuts on the cover be tightened?
Tighten the nuts evenly starting from the centre of the glass
What should be done with the gauge valves if the boiler is in service?
Do not open the gauge valves until the new glass is heated up
What is the purpose of the bicolour gauge glass?
To show the steam and water levels as different colours
What is indicated by the red light in a bicolour gauge glass?
The steam space in the boiler drum
Why does the gauge glass generally indicate a water level lower than the actual level in the boiler drum?
Because the water in the gauge glass is cooler and denser than the water in the boiler drum
What is the purpose of the mirrors in the bicolour gauge glass?
To reflect the red and green light to the operating floor
What is required by ASME BPVC I Part PG-60.1.1.1?
A fibre optic cable or mirrors to transfer the optical image of the water level
What is the purpose of cracking open the steam valve?
To slowly blow steam through to heat the glass further
What should be done after the glass is at operating temperature?
Open the steam and water valves fully
What is the purpose of the shutter in a coloured screen remote level indicator?
To separate the blue and red colours
What is the purpose of the dirt traps in a remote level indicator?
To prevent contamination of the indicating liquid
What is the advantage of an electronic remote water level indicator?
It has no moving mechanical parts
What is the function of the water detection probes in a remote water level indicator?
To detect the presence of water or steam
What is the purpose of the electronic detection and verification unit in a remote water level indicator?
To determine the validity of the reading and transmit the level to LED displays
What is the purpose of the digital water level indicator in Figure 27?
To display the level on an LCD display in user-configurable engineering units
What is the function of the camera in Figure 28?
To monitor the water levels and transmit the information to the control room
What is the colour of the liquid in the manometer?
Blue or green
What is the consequence of overfilling the indicating liquid in a remote level indicator?
The indicated level will be too high
What is the function of the LED display in a remote water level indicator?
To display the level received from the electronic detection and verification unit
What are the factors that can affect the error in a gauge glass?
Ambient temperature and length of the gauge glass
Why is it important to keep piping connections to water level controls clear?
To ensure accurate water level readings
What happens when steam connection piping is blocked?
Steam condenses and forms a vacuum
Why is regular blowing down of the water column and gauge glass necessary?
To remove sediment that may collect
What is the purpose of a remote water level indicator?
To show the water level at a remote location
How often should the water column and gauge glass be blown down on smaller high-pressure boilers?
Every shift
Why should gauge glasses be renewed?
If they become obscured by internal corrosion or deposits
What is the purpose of ASME BPVC I Part PG-60.1.1.1?
To provide guidelines for remote water level indicators
What is the operating element of the remote water level indicator in Figure 24?
A large sensitive diaphragm
What happens when the water level in the drum rises in the remote water level indicator?
The diaphragm moves up
What is the primary purpose of having a gauge glass in a boiler?
To continuously monitor the boiler water level
Which of the following boilers is required to have a permanent indicator of the lowest permissible water level?
Heating boilers
What is the minimum distance required between the lowest visible water level in a gauge glass and the lowest permissible water level in a power boiler?
2 in. (50 mm)
What is the alternative to one of the required gauge glasses for boilers, according to ASME BPVC I Part PG-60.1.1.1?
Remote water level indicator
What is the primary purpose of the valved fittings attached to the water column or boiler in a heating boiler?
To provide a way to attach the gauge glass
What is the main purpose of the safety shutoff device in the lower valve on the gauge glass?
To prevent fluid from escaping when the gauge glass breaks
What is the minimum diameter of the unrestricted drain opening required for steam heating boilers, according to ASME BPVC IV Part HG-603?
1/4 in. (6 mm)
Why is it critical to know the boiler water level at all times, especially with boilers operating at higher pressures?
To prevent unsafe operation and potential damage to the boiler
What is the purpose of the washer or packing ring and a nut at each end of the gauge glass tube?
To hold the gauge glass tube tightly in place
What is the purpose of having both direct and indirect methods of determining the boiler water level?
To provide a redundant system for safety
What determines the pressure ratings of gauge glass tubing?
All of the above
What is the limitation of using tubular gauge glasses?
They are limited to relatively lower pressures and temperatures
MEDIUM What is the purpose of the metal rods or transparent shield surrounding the gauge glass?
To protect the gauge glass from breakage
What is the requirement for installing multiple gauge glasses?
The visible portions of the gauge glasses must overlap
What is the purpose of the drain valve or cock on the lower gauge glass fitting?
To remove any solid material that may collect
What is the minimum overlap required for adjoining sections of gauge glass assemblies?
1 in. (25 mm)
What is the purpose of the isolating valves above and below the gauge glass connections?
To isolate the gauge glass for maintenance
What is the purpose of the chains attached to the valve spindles?
To operate the valves from ground level if the boiler drum is located too high to reach
Which type of boilers have a different requirement for the location of the gauge glass in relation to the lowest permissible water level?
Horizontal firetube boilers and locomotive boilers
What is the main reason for the failure of tubular gauge glasses?
Corrosion caused by alkalinity and silica depletion
What is the purpose of the water column in the installation shown in Figure 16?
To act as a reservoir to dampen agitation in the water
What should be done first when a gauge glass fails?
Shut off the steam and water valves on the gauge
What should be applied to the washers when installing a new gauge glass?
Graphite
Why should the operator wear a face shield when replacing a gauge glass?
To prevent injury from flying glass fragments
What is the purpose of the drain valve in the installation shown in Figure 15?
To permit all the connections to be blown through
What is the requirement for the location of the gauge glass in relation to the lowest permissible water level in a steam heating boiler?
The lowest visible water level in the gauge glass must be at least 1 in. above the lowest permissible water level
What is the purpose of the water column in relation to the gauge glass connections?
To trap sludge or sediment and prevent it from collecting in the gauge glass connections
What is the requirement for tightening the nuts on the gauge glass?
The nuts should be only hand tightened
What is the correct procedure for tightening the nuts on the cover?
Tighten the nuts on the cover evenly, starting from the centre of the glass.
Why is it necessary to heat the gauge glass slowly when putting it into service?
To prevent the glass from breaking due to thermal shock
What type of gauge glass is suitable for high pressure steam applications and can also be used for caustic and acidic liquids?
Armored-type (flat) gauge glass
What is the purpose of allowing the new glass to warm up gradually in a boiler?
To prevent thermal shock to the glass.
What should be done when the gauge glass leaks when put into service?
Close the steam and water valves, and open the drain before tightening the nuts
What is the function of the green and red filters in a bicolour gauge glass?
To diffract the light and indicate the water level.
Why is the gauge glass generally lower than the actual level in the boiler drum?
Because the water in the gauge glass is cooler and denser than the water in the boiler drum.
What is the purpose of the mica coating on the inside surfaces of the glasses?
To provide a clear view of the liquid level
What is the purpose of the mirrors in a bicolour gauge glass installation?
To direct the light from the gauge glass to the operator.
Why should the operator wear a face shield when opening the valves?
To prevent injury from flying debris
What is the correct sequence of steps when replacing the gauge glass in a boiler?
Install new glass, replace the cover, and tighten the nuts.
What should be done when replacing the armored-type (flat) gauge glass?
Apply molybdenum disulfide to the threads of the studs
What is the limitation of using tubular gauge glasses?
They are not suitable for high pressure steam applications
What is the purpose of cracking open the steam valve during the replacement of the gauge glass?
To heat the new glass further.
What happens when the mica coating on the inside surfaces of the glasses becomes opaque?
Water is now directly contacting the glass
What is the purpose of the circulating tie bar in a bicolour gauge glass?
To provide a connection point for the gauge valves.
What is the requirement for indicating the drum level in a boiler with a gauge glass?
The gauge glass must be visible from the operating floor.
What should be done when checking the gauge glass for level?
Wait for the water level to stabilize
What is the purpose of the reflex gauge?
To create a sharp line of demarcation at the liquid level
What is the purpose of the water valve in the installation of a new gauge glass?
To allow water to enter the boiler.
What is the purpose of the shutter in a coloured screen remote level indicator?
To separate the blue and red colours
What is the function of the dirt traps in a remote level indicator?
To prevent contamination of the indicating liquid
What type of liquid is used in the manometer of a remote level indicator?
Insoluble liquid denser than water
What is the advantage of using an electronic remote water level indicator?
It has no moving mechanical parts
What is the purpose of the LED displays in a remote water level indicator?
To display the water level reading
What is the effect of a closed valve on the steam connection piping?
The steam in the gauge glass condenses, forming a vacuum.
What is the result of a blocked water connection piping?
The condensate accumulates in the float cage, column, or gauge glass.
What is the purpose of the cameras in a remote water level indicator?
To monitor the water level and transmit the information to the control room
What is the unit of measurement displayed on the digital water level indicator in Figure 27?
Millimetres
Why is it necessary to keep piping connections to water level controls, water columns, and gauge glasses clear?
To ensure accurate communication of the boiler water level to the level instruments.
What is the purpose of blowing down the water column and gauge glass?
To remove sediment that may collect.
What happens when the drum level rises in a coloured screen remote level indicator?
The shutter moves upwards
What is the purpose of the water column in a remote water level indicator?
To connect the steam condenser to the boiler
What is the recommended frequency of blowing down the gauge glass on large boilers?
Less frequently, to avoid shortening the life of the mica.
What is the purpose of remote water level indicators?
To show the water level at a remote location.
What is the function of the probes in a remote water level indicator?
To detect the presence of water or steam
What is the operating principle of the mechanical remote water level indicator shown in Figure 24?
It uses a spring to balance the pressure on the two sides of the diaphragm.
What is the effect of boiler pressure on the movement of the diaphragm in the mechanical remote water level indicator?
It has no effect on the movement of the diaphragm.
What is required by ASME BPVC I Part PG-60.1.1.1 for boilers where the water level is not readily visible to the operator?
A combination of two of the following: an independent remote water level indicator, an independent continuous transmission and display of an image of the water level, or a fiber optic cable.
What is the purpose of regular water column, gauge glass, and level control blow down?
To remove sediment that may collect and ensure accurate communication of the boiler water level.
HARD What is the minimum number of gage glasses required for boilers with a maximum allowable working pressure not exceeding 400 psi, according to ASME BPVC I Part PG-60.1?
One
What is the purpose of the drain valve in the lower fitting of the gage glass on a steam heating boiler, according to ASME BPVC IV Part HG-603?
To facilitate cleaning
What is the minimum diameter of the unrestricted drain opening required for steam heating boilers, according to ASME BPVC IV Part HG-603?
¼ in.
What is the alternative to one of the required gage glasses for boilers, according to ASME BPVC I Part PG-60.1.1.1?
A remote water level indicator
What is the minimum distance required between the lowest visible water level in a gage glass and the lowest permissible water level, according to ASME BPVC IV Part HG-603?
1 in.
What is the purpose of the valved fittings attached to the water column or boiler on a steam heating boiler, according to ASME BPVC IV Part HG-603?
To attach the gage glass
What is required by ASME BPVC I Part PG-60.1 for boilers having a maximum allowable working pressure exceeding 400 psi?
Two gage glasses
What is the purpose of the permanent indicator of the lowest permissible water level on a steam heating boiler?
To indicate the lowest permissible water level
What is the recommended procedure for tightening the bolts on a transparent gauge glass?
Tightening the bolts from the centre outwards
What is the purpose of the mica coating on the inside surfaces of the glasses in a transparent gauge glass?
To prevent water from contacting the glass
Why must the gauge glass be inserted into the steam fitting first and then lowered into the bottom of the water fitting before tightening the nuts?
To ensure the glass is properly aligned
What is the primary purpose of a reflex gauge glass?
To create a sharp line of demarcation at the liquid level
What should be done before tightening the nuts on a gauge glass that has been replaced?
Apply molybdenum disulfide to the contact surfaces
What is the primary advantage of using a flat gauge glass?
It is suitable for high-pressure steam applications
Why should the operator wear a face shield when opening the valves?
To prevent injury from sudden valve opening
What is the purpose of the crossover method of tightening the bolts on a transparent gauge glass?
To ensure even pressure on the glass
What should be done when a gauge glass leaks during initial installation?
Close the steam and water valves and open the drain
What is the primary purpose of polishing the gauge surfaces when replacing a gauge glass?
To ensure the gasket material does not plug the valves
What is the main reason for the requirement of a greater safety margin for power boiler water level indicators as opposed to those for heating boilers?
Due to the higher operating pressure of power boilers
What is the purpose of the water column in the installation shown in Figure 16?
To act as a reservoir to dampen agitation in the water
What is the consequence of misalignment of fittings on the gauge glass?
It causes premature gauge glass failure
What is the recommended method for cutting a new gauge glass to the correct length?
Using a glass cutter
What is the purpose of putting graphite on the washers when installing a new gauge glass?
To act as a lubricant between the washers and nuts
What is the requirement for the location of the gauge glass in relation to the lowest permissible water level in a horizontal firetube boiler with a diameter greater than 400 mm?
The lowest visible water level in the gauge glass must be at least 75 mm above the lowest permissible water level
What is the purpose of the drain valve on the gauge glass fitting?
To permit all the connections to be blown through
Why should the nuts on the gauge glass be tightened alternately?
To prevent the glass from turning when tightening the nuts
What is the consequence of not cracking open the gauge glass valves when replacing a gauge glass?
The gauge glass may shatter due to fragments of glass
What is the purpose of the water column in relation to the gauge glass connections?
To trap sludge or sediment in the gauge glass connections
What is the main reason why the gauge glass generally indicates a water level lower than the actual level in the boiler drum?
The density of the water in the gauge glass is higher than the density of the water in the boiler drum.
What is the purpose of cracking open the steam valve?
To allow the new glass to warm up gradually.
What is the purpose of the mirrors in the bicolour gauge glass?
To reflect the red and green light to the control area.
What is required by ASME BPVC I Part PG-60.1.1.1?
A fibre optic cable or mirrors must be used to transfer the optical image of the water level to the control area.
What is the purpose of the bicolour gauge glass?
To indicate the steam and water levels separately.
Why is it important to allow the new glass to warm up gradually?
To prevent the glass from breaking.
What is the purpose of the green light in a bicolour gauge glass?
To indicate the water level in the boiler.
How should the nuts on the cover be tightened?
Tighten the nuts on the cover starting from the centre of the glass.
What should be done after the glass is at operating temperature?
Close the drain valve and open the steam valve.
Why should the old gauge glasses not be reused?
All of the above.
What is the effect of a blocked steam connection piping on the water level in the gauge glass?
The steam in the gauge glass will condense, forming a vacuum that draws water in, causing the operators to believe the boiler is full of water.
Why is it necessary to blow down the water column and gauge glass regularly?
To remove sediment that may collect and affect the water level reading.
What is the purpose of the condenser at the boiler drum in a remote water level indicator?
To maintain a constant head of water pressure on the steam side.
What is the result of a blocked water connection piping on the steam in the gauge glass?
The steam will condense and accumulate in the float cage, column, or gauge glass.
What is the purpose of the mica coating on the inside surfaces of the gauge glasses?
To protect the gauge glass from internal corrosion or deposits.
Why is it necessary to keep the piping connections to water level controls, water columns, and gauge glasses clear?
To ensure the boiler water level is properly communicated to the level instruments.
What is the consequence of not blowing down the water column and gauge glass regularly?
The water level reading will be inaccurate due to sediment accumulation.
What is the purpose of the spring in a remote water level indicator?
To balance the difference in head pressure on the two sides of the diaphragm.
What is the result of a closed valve on the water level control piping?
The steam in the gauge glass will condense and form a vacuum that draws water in.
What is the requirement for installing multiple gauge glasses, according to ASME BPVC I Part PG-60.1.1.1?
A combination of two of the above options shall be provided.
What is the purpose of the transparent leg in a manometer-based remote level indicator?
To provide a constant head of water acting on one leg of the manometer
What is the advantage of using an electronic remote water level indicator?
It has no moving mechanical parts
What is the purpose of the shutter in a coloured screen remote level indicator?
To separate the blue and red colours in the indicator
What is the function of the detection and verification unit in an electronic remote water level indicator?
To determine the validity of the reading and transmit the level to LED displays
What is the purpose of the digital water level indicator shown in Figure 27?
To display the level in user-configurable engineering units
What is the advantage of using a remote water level indicator with multiple displays?
It can be located up to three different locations
What is the purpose of the cameras in the remote water level indicator system shown in Figure 28?
To monitor the water levels and transmit the information to the control room
What is the consequence of overfilling the indicating liquid in a manometer-based remote level indicator?
The indicated level will be too high
What is the purpose of the dirt traps in a manometer-based remote level indicator?
To prevent contamination of the indicating liquid
What is the function of the probes in an electronic remote water level indicator?
To detect the presence of water or steam in the boiler
What is the purpose of the stainless steel check ball in the lower valve on the gauge glass?
To stop the flow of fluid in case the gauge glass breaks
Why are tubular gauge glasses limited to relatively lower pressures and temperatures?
Because their pressure ratings are determined by the manufacturer
What is the minimum overlap required for adjoining sections of gauge glass assemblies?
1 in. (25 mm)
What determines the pressure ratings of gauge glass tubing?
All of the above
Why are metal rods or a transparent shield used to surround the gauge glass?
To protect the gauge glass from breakage
What is the purpose of the washers or packing rings and nuts at each end of the gauge glass tube?
To hold the gauge glass tightly in place
What is the minimum size of piping required for connecting a water column to a steam boiler?
NPS 1 (DN 25)
What is the purpose of the drain valve or cock on the lower gauge glass fitting?
To remove solid material that may collect
What is the limitation of using tubular gauge glasses?
They are limited to relatively lower pressures and temperatures
What is the purpose of the valved fittings attached to the water column or boiler?
To blow down the water column
Study Notes
Boiler Water Level Measurement
- Boiler water level can be measured using direct or indirect methods.
- Direct methods include gauge glasses of various designs.
- Indirect methods include remote water level indicators.
ASME BPVC Code Requirements
- ASME BPVC I Part PG-60.1 requires at least one gauge glass for boilers with a fixed water level.
- Boilers with a maximum allowable working pressure exceeding 400 psi (3 MPa) require two gauge glasses.
- The lowest visible water level in a gauge glass must be at least 2 in. (50 mm) above the lowest permissible water level.
- ASME BPVC I Part PG-60.1.1.1 allows for the use of remote water level indicators.
Gauge Glass Types
- Tubular gauge glasses:
- Simplest and least costly design.
- Limited to relatively lower pressures and temperatures.
- Excessively long gauge glasses should be avoided.
- Armored-type (flat) gauge glasses:
- Used for higher pressures and temperatures.
- Consist of glass plates bolted in a steel forged housing.
- Bicolour gauge glasses:
- Show steam and water as different colours.
- Permit easy identification of the water level at a distance.
Gauge Glass Installation and Maintenance
- Gauge glasses can be connected directly to the shell or drum of the boiler, or to an intervening water column.
- ASME BPVC I Part PG-60.3.1 and BPVC IV Part HG-603 permit gauge glasses to be connected to a single water column.
- Gauge glasses should be replaced if they become corroded or damaged.
- Replacement of tubular gauge glasses involves shutting off steam and water valves, opening the drain valve, and removing the broken glass.
Error in Gauge Glass Measurement
- Gauge glasses generally indicate a water level lower than the actual level in the boiler drum.
- Error is affected by factors such as ambient temperature, length of the gauge glass, and level of the liquid in the gauge glass.
Testing of Water Column and Gauge Glass During Operation
-
Water and steam connections to both a water column and a gauge glass must always be unobstructed.
-
Regular water column, gauge glass, and level control blow down is recommended to remove sediment and ensure accurate water level measurement.### Remote Water Level Indicators
-
Remote water level indicators are used to show the water level at a remote location, such as in a control room, adjacent to boiler blowoff valves, or at particular operating locations.
ASME BPVC I Part PG-60.1.1.1 Requirements
- When the water level in at least one gage glass is not readily visible to the operator in the area where control actions are initiated, a remote water level indicator is required.
- The indicator can be a fiber optic cable, mirrors, or a combination of two of the following: an independent remote water level indicator, and an independent continuous transmission and display of an image of the water level in a gage glass.
Mechanical Remote Water Level Indicators
- Figure 24 shows a type of remote water level indicator of entirely mechanical operation.
- The operating element consists of a large sensitive diaphragm with the top side connected to the steam space of the boiler, and the bottom to the water space.
- The diaphragm moves up and down in accordance with the water level.
- Coloured screens illuminate the inside of the indicator with blue in the lower portion, representing the water, and red in the upper part to represent steam.
Manometer Remote Water Level Indicators
- Figure 25 shows a type of remote level indicator that is basically a manometer with one transparent leg.
- The manometer is filled with a blue or green insoluble liquid that is denser than water.
- The indicating liquid rises in the glass, and shows the level to engineers on the operating floor as the drum level rises.
Electronic Remote Water Level Indicators
- Figure 26 shows a common type of remote water level indicator that uses electronic devices to sense and transmit level.
- The system is comprised of three major components: a water column with up to 24 water detection probes, an electronic detection and verification unit, and one or more remote LED displays.
- The probes detect the presence of water or steam, and the detection and verification unit determines the validity of the reading, and transmits the level to LED displays.
Digital Water Level Indicators
- Figure 27 shows a digital water level indicator that receives a standard 4 to 20 mA signal from a drum level transmitter, and displays the level on an LCD display, in user-configurable engineering units.
- The indicator shows drum level in millimetres, with levels above or below set point indicated as positive or negative readings.
Remote Water Level Indicators in Control Rooms
- Figure 28 shows four reflex-type gauge glasses for four different boilers, displayed on a single computer display, in a central control room.
- Cameras monitor the water levels and transmit the information to the control room in real time.
ASME BPVC I Part PG-60.1.1.2 Requirements
- The display of a remote water level indicator shall have a clearly marked minimum water level reference at least 2 in.(50 mm) above the lowest permissible water level, as determined by the Manufacturer.
Boiler Water Level Measurement
- Boiler water level can be measured using direct or indirect methods.
- Direct methods include gauge glasses of various designs.
- Indirect methods include remote water level indicators.
ASME BPVC Code Requirements
- ASME BPVC I Part PG-60.1 requires at least one gauge glass for boilers with a fixed water level.
- Boilers with a maximum allowable working pressure exceeding 400 psi (3 MPa) require two gauge glasses.
- The lowest visible water level in a gauge glass must be at least 2 in. (50 mm) above the lowest permissible water level.
- ASME BPVC I Part PG-60.1.1.1 allows for the use of remote water level indicators.
Gauge Glass Types
- Tubular gauge glasses:
- Simplest and least costly design.
- Limited to relatively lower pressures and temperatures.
- Excessively long gauge glasses should be avoided.
- Armored-type (flat) gauge glasses:
- Used for higher pressures and temperatures.
- Consist of glass plates bolted in a steel forged housing.
- Bicolour gauge glasses:
- Show steam and water as different colours.
- Permit easy identification of the water level at a distance.
Gauge Glass Installation and Maintenance
- Gauge glasses can be connected directly to the shell or drum of the boiler, or to an intervening water column.
- ASME BPVC I Part PG-60.3.1 and BPVC IV Part HG-603 permit gauge glasses to be connected to a single water column.
- Gauge glasses should be replaced if they become corroded or damaged.
- Replacement of tubular gauge glasses involves shutting off steam and water valves, opening the drain valve, and removing the broken glass.
Error in Gauge Glass Measurement
- Gauge glasses generally indicate a water level lower than the actual level in the boiler drum.
- Error is affected by factors such as ambient temperature, length of the gauge glass, and level of the liquid in the gauge glass.
Testing of Water Column and Gauge Glass During Operation
-
Water and steam connections to both a water column and a gauge glass must always be unobstructed.
-
Regular water column, gauge glass, and level control blow down is recommended to remove sediment and ensure accurate water level measurement.### Remote Water Level Indicators
-
Remote water level indicators are used to show the water level at a remote location, such as in a control room, adjacent to boiler blowoff valves, or at particular operating locations.
ASME BPVC I Part PG-60.1.1.1 Requirements
- When the water level in at least one gage glass is not readily visible to the operator in the area where control actions are initiated, a remote water level indicator is required.
- The indicator can be a fiber optic cable, mirrors, or a combination of two of the following: an independent remote water level indicator, and an independent continuous transmission and display of an image of the water level in a gage glass.
Mechanical Remote Water Level Indicators
- Figure 24 shows a type of remote water level indicator of entirely mechanical operation.
- The operating element consists of a large sensitive diaphragm with the top side connected to the steam space of the boiler, and the bottom to the water space.
- The diaphragm moves up and down in accordance with the water level.
- Coloured screens illuminate the inside of the indicator with blue in the lower portion, representing the water, and red in the upper part to represent steam.
Manometer Remote Water Level Indicators
- Figure 25 shows a type of remote level indicator that is basically a manometer with one transparent leg.
- The manometer is filled with a blue or green insoluble liquid that is denser than water.
- The indicating liquid rises in the glass, and shows the level to engineers on the operating floor as the drum level rises.
Electronic Remote Water Level Indicators
- Figure 26 shows a common type of remote water level indicator that uses electronic devices to sense and transmit level.
- The system is comprised of three major components: a water column with up to 24 water detection probes, an electronic detection and verification unit, and one or more remote LED displays.
- The probes detect the presence of water or steam, and the detection and verification unit determines the validity of the reading, and transmits the level to LED displays.
Digital Water Level Indicators
- Figure 27 shows a digital water level indicator that receives a standard 4 to 20 mA signal from a drum level transmitter, and displays the level on an LCD display, in user-configurable engineering units.
- The indicator shows drum level in millimetres, with levels above or below set point indicated as positive or negative readings.
Remote Water Level Indicators in Control Rooms
- Figure 28 shows four reflex-type gauge glasses for four different boilers, displayed on a single computer display, in a central control room.
- Cameras monitor the water levels and transmit the information to the control room in real time.
ASME BPVC I Part PG-60.1.1.2 Requirements
- The display of a remote water level indicator shall have a clearly marked minimum water level reference at least 2 in.(50 mm) above the lowest permissible water level, as determined by the Manufacturer.
Boiler Water Level Measurement
- Boiler water level can be measured using direct or indirect methods.
- Direct methods include gauge glasses of various designs.
- Indirect methods include remote water level indicators.
ASME BPVC Code Requirements
- ASME BPVC I Part PG-60.1 requires at least one gauge glass for boilers with a fixed water level.
- Boilers with a maximum allowable working pressure exceeding 400 psi (3 MPa) require two gauge glasses.
- The lowest visible water level in a gauge glass must be at least 2 in. (50 mm) above the lowest permissible water level.
- ASME BPVC I Part PG-60.1.1.1 allows for the use of remote water level indicators.
Gauge Glass Types
- Tubular gauge glasses:
- Simplest and least costly design.
- Limited to relatively lower pressures and temperatures.
- Excessively long gauge glasses should be avoided.
- Armored-type (flat) gauge glasses:
- Used for higher pressures and temperatures.
- Consist of glass plates bolted in a steel forged housing.
- Bicolour gauge glasses:
- Show steam and water as different colours.
- Permit easy identification of the water level at a distance.
Gauge Glass Installation and Maintenance
- Gauge glasses can be connected directly to the shell or drum of the boiler, or to an intervening water column.
- ASME BPVC I Part PG-60.3.1 and BPVC IV Part HG-603 permit gauge glasses to be connected to a single water column.
- Gauge glasses should be replaced if they become corroded or damaged.
- Replacement of tubular gauge glasses involves shutting off steam and water valves, opening the drain valve, and removing the broken glass.
Error in Gauge Glass Measurement
- Gauge glasses generally indicate a water level lower than the actual level in the boiler drum.
- Error is affected by factors such as ambient temperature, length of the gauge glass, and level of the liquid in the gauge glass.
Testing of Water Column and Gauge Glass During Operation
-
Water and steam connections to both a water column and a gauge glass must always be unobstructed.
-
Regular water column, gauge glass, and level control blow down is recommended to remove sediment and ensure accurate water level measurement.### Remote Water Level Indicators
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Remote water level indicators are used to show the water level at a remote location, such as in a control room, adjacent to boiler blowoff valves, or at particular operating locations.
ASME BPVC I Part PG-60.1.1.1 Requirements
- When the water level in at least one gage glass is not readily visible to the operator in the area where control actions are initiated, a remote water level indicator is required.
- The indicator can be a fiber optic cable, mirrors, or a combination of two of the following: an independent remote water level indicator, and an independent continuous transmission and display of an image of the water level in a gage glass.
Mechanical Remote Water Level Indicators
- Figure 24 shows a type of remote water level indicator of entirely mechanical operation.
- The operating element consists of a large sensitive diaphragm with the top side connected to the steam space of the boiler, and the bottom to the water space.
- The diaphragm moves up and down in accordance with the water level.
- Coloured screens illuminate the inside of the indicator with blue in the lower portion, representing the water, and red in the upper part to represent steam.
Manometer Remote Water Level Indicators
- Figure 25 shows a type of remote level indicator that is basically a manometer with one transparent leg.
- The manometer is filled with a blue or green insoluble liquid that is denser than water.
- The indicating liquid rises in the glass, and shows the level to engineers on the operating floor as the drum level rises.
Electronic Remote Water Level Indicators
- Figure 26 shows a common type of remote water level indicator that uses electronic devices to sense and transmit level.
- The system is comprised of three major components: a water column with up to 24 water detection probes, an electronic detection and verification unit, and one or more remote LED displays.
- The probes detect the presence of water or steam, and the detection and verification unit determines the validity of the reading, and transmits the level to LED displays.
Digital Water Level Indicators
- Figure 27 shows a digital water level indicator that receives a standard 4 to 20 mA signal from a drum level transmitter, and displays the level on an LCD display, in user-configurable engineering units.
- The indicator shows drum level in millimetres, with levels above or below set point indicated as positive or negative readings.
Remote Water Level Indicators in Control Rooms
- Figure 28 shows four reflex-type gauge glasses for four different boilers, displayed on a single computer display, in a central control room.
- Cameras monitor the water levels and transmit the information to the control room in real time.
ASME BPVC I Part PG-60.1.1.2 Requirements
- The display of a remote water level indicator shall have a clearly marked minimum water level reference at least 2 in.(50 mm) above the lowest permissible water level, as determined by the Manufacturer.
Learn about the methods of measuring boiler water level, including direct and indirect methods, and the ASME BPVC code requirements for gauge glasses on boilers.
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