All boilers must be fitted with at least one pressure indicator.
The usual type is a simple pressure gauge constructed to EN 12953.
The dial should be at least 150 mm in diameter and of the Bourdon tube type, it should be marked to indicate the normal working pressure and the maximum permissible working pressure / design pressure.
Pressure gauges are connected to the steam space of the boiler and usually have a ring type siphon tube which fills with condensed steam and protects the dial mechanism from high temperatures.
Pressure gauges may be fitted to other pressure containers such as blowdown vessels, and will usually have smaller dials as shown in Figure 3.7.9.
Typical pressure gauge with ring siphon
Gauge glasses and fittings
All steam boilers are fitted with at least one water level indicator, but those with a rating of 100 kW or more should be fitted with two indicators. The indicators are usually referred to as gauge glasses complying with EN 12953.
Fig. 3.7.10
Gauge glass and fittings
A gauge glass shows the current level of water in the boiler, regardless of the boiler's operating conditions. Gauge glasses should be installed so that their lowest reading will show the water level at 50 mm above the point where overheating will occur. They should also be fitted with a protector around them, but this should not hinder visibility of the water level. Figure 3.7.10 shows a typical gauge glass.
Gauge glasses are prone to damage from a number of sources, such as corrosion from the chemicals in boiler water, and erosion during blowdown, particularly at the steam end. Any sign of corrosion or erosion indicates that a new glass is required.
When testing the gauge glass steam connection, the water cock should be closed. When testing the gauge glass water connections, the steam cock pipe should be closed.
To test a gauge glass, the following procedure should be followed:
Close the water cock and open the drain cock for approximately 5 seconds.
Close the drain cock and open the water cock.
Water should return to its normal working level relatively quickly. If this does not happen, then a blockage in the water cock could be the reason, and remedial action should be taken as soon as possible.
Close the steam cock and open the drain cock for approximately 5 seconds.
Close the drain cock and open the steam cock.
If the water does not return to its normal working level relatively quickly, a blockage may exist in the steam cock. Remedial action should be taken as soon as possible.
The authorised attendant should systematically test the water gauges at least once each day and should be provided with suitable protection for the face and hands, as a safeguard against scalding in the event of glass breakage.
Note: that all handles for the gauge glass cocks should point downwards when in the running condition.
Gauge glass guards
The gauge glass guard should be kept clean. When the guard is being cleaned in place, or removed for cleaning, the gauge should be temporarily shut-off.
Make sure there is a satisfactory water level before shutting off the gauge and take care not to touch or knock the gauge glass. After cleaning, and when the guard has been replaced, the gauge should be tested and the cocks set in the correct position.
The usual type is a simple pressure gauge constructed to EN 12953.
The dial should be at least 150 mm in diameter and of the Bourdon tube type, it should be marked to indicate the normal working pressure and the maximum permissible working pressure / design pressure.
Pressure gauges are connected to the steam space of the boiler and usually have a ring type siphon tube which fills with condensed steam and protects the dial mechanism from high temperatures.
Pressure gauges may be fitted to other pressure containers such as blowdown vessels, and will usually have smaller dials as shown in Figure 3.7.9.
Typical pressure gauge with ring siphon
Gauge glasses and fittings
All steam boilers are fitted with at least one water level indicator, but those with a rating of 100 kW or more should be fitted with two indicators. The indicators are usually referred to as gauge glasses complying with EN 12953.
Fig. 3.7.10Gauge glass and fittings
A gauge glass shows the current level of water in the boiler, regardless of the boiler's operating conditions. Gauge glasses should be installed so that their lowest reading will show the water level at 50 mm above the point where overheating will occur. They should also be fitted with a protector around them, but this should not hinder visibility of the water level. Figure 3.7.10 shows a typical gauge glass.
Gauge glasses are prone to damage from a number of sources, such as corrosion from the chemicals in boiler water, and erosion during blowdown, particularly at the steam end. Any sign of corrosion or erosion indicates that a new glass is required.
When testing the gauge glass steam connection, the water cock should be closed. When testing the gauge glass water connections, the steam cock pipe should be closed.
To test a gauge glass, the following procedure should be followed:
Close the water cock and open the drain cock for approximately 5 seconds.
Close the drain cock and open the water cock.
Water should return to its normal working level relatively quickly. If this does not happen, then a blockage in the water cock could be the reason, and remedial action should be taken as soon as possible.
Close the steam cock and open the drain cock for approximately 5 seconds.
Close the drain cock and open the steam cock.
If the water does not return to its normal working level relatively quickly, a blockage may exist in the steam cock. Remedial action should be taken as soon as possible.
The authorised attendant should systematically test the water gauges at least once each day and should be provided with suitable protection for the face and hands, as a safeguard against scalding in the event of glass breakage.
Note: that all handles for the gauge glass cocks should point downwards when in the running condition.
Gauge glass guards
The gauge glass guard should be kept clean. When the guard is being cleaned in place, or removed for cleaning, the gauge should be temporarily shut-off.
Make sure there is a satisfactory water level before shutting off the gauge and take care not to touch or knock the gauge glass. After cleaning, and when the guard has been replaced, the gauge should be tested and the cocks set in the correct position.
Maintenance
The gauge glass should be thoroughly overhauled at each annual survey. Lack of maintenance can result in hardening of packing and seizure of cocks. If a cock handle becomes bent or distorted special care is necessary to ensure that the cock is set full open. A damaged fitting should be renewed or repaired immediately. Gauge glasses often become discoloured due to water conditions; they also become thin and worn due to erosion. Glasses, therefore, should be renewed at regular intervals.
A stock of spare glasses and cone packing should always be available in the boiler house. Remember:
If steam passes are choked a false high water level may be given in the gauge glass. After the gauge has been tested a false high water level may still be indicated.
If the water passages are choked an artificially high water level may be observed due to steam condensing in the glass. After testing, the glass will tend to remain empty unless the water level in the boiler is higher than the top connection, in which case water might flow into the glass from this connection.
Gauge glass levels must be treated with the utmost respect, as they are the only visual indicator of water level conditions inside the boiler. Any water level perceived as abnormal must be investigated as soon as it is observed, with immediate action taken to shut down the boiler burner if necessary.
The gauge glass should be thoroughly overhauled at each annual survey. Lack of maintenance can result in hardening of packing and seizure of cocks. If a cock handle becomes bent or distorted special care is necessary to ensure that the cock is set full open. A damaged fitting should be renewed or repaired immediately. Gauge glasses often become discoloured due to water conditions; they also become thin and worn due to erosion. Glasses, therefore, should be renewed at regular intervals.
A stock of spare glasses and cone packing should always be available in the boiler house. Remember:
If steam passes are choked a false high water level may be given in the gauge glass. After the gauge has been tested a false high water level may still be indicated.
If the water passages are choked an artificially high water level may be observed due to steam condensing in the glass. After testing, the glass will tend to remain empty unless the water level in the boiler is higher than the top connection, in which case water might flow into the glass from this connection.
Gauge glass levels must be treated with the utmost respect, as they are the only visual indicator of water level conditions inside the boiler. Any water level perceived as abnormal must be investigated as soon as it is observed, with immediate action taken to shut down the boiler burner if necessary.
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