Questions and Answers
What is the purpose of the pressure gauge on a steam boiler?
To indicate the internal pressure of the boiler
Why is it important for the pressure gauge dial to be graduated to approximately double the safety valve setting?
To indicate if the boiler is at its normal operating temperature
What type of pressure gauge is commonly used for indicating the boiler's internal pressure?
Bourdon tube gauge
Why must each boiler have a pressure gauge so located that it is easily readable?
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What is the purpose of a shutoff valve or cock in the gauge connection adjacent to the gauge?
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Why is a syphon or equivalent device required to protect the pressure gauge in a steam boiler?
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What are siphons used for in steam boilers?
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According to ASME BPVC I Part PG-60.6.3, what is required for each boiler during operation to ensure the accuracy of the boiler pressure gauge?
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What is the minimum size requirement for siphons used in piping for steam boilers?
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What is the purpose of an inspector gauge connection for low-pressure boilers?
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Study Notes
- The pressure gauge in a steam boiler must be connected to the steam space or water column to reduce the likelihood of blockage and maintain accurate pressure readings.
- Part PG-60.6.1 requires a shutoff valve or cock in the gauge connection adjacent to the gauge, prohibiting the installation of any other valves between the gauge and the boiler.
- The shutoff valve is important for permitting the replacement of the perfect pressure gauge while the boiler is in operation and for installing a master test pressure gauge to verify the accuracy of the boiler pressure gauge.
- To protect the pressure gauge from high pressure and temperature steam, a syphon or equivalent device is required to maintain a water seal and prevent steam from entering the gauge tube.
- Piping or siphons for steam boilers must meet minimum dimensions: NPS ¼ (DN 8) for connections to the boiler, except the syphon, and ¼ in. (6 mm) for the minimum size of a syphon.
- Siphons, which are liquid seals shaped in a spiral pattern or a "U," work by trapping condensate at the lower portion of the pigtail or U, which keeps steam away from the pressure-sensing device while still transmitting pressure to the gauge.
- ASME BPVC I Part PG-60.6.3 requires each boiler to have a valve connection for attaching a test gauge during operation to ensure the accuracy of the boiler pressure gauge.
- Low-pressure steam boilers must have a steam gauge or compound steam gauge connected to the steam space or water column or steam connection with a siphon or equivalent device for preventing steam from entering the gauge tube.
- The gauge connection, boiler tapping, or piping to the boiler must not be less than DN 8 (NPS ¼) or DN 15 (NPS ½) for steel or wrought iron pipe or tubing, and the scale on the dial of the steam boiler gauge must be graduated to not less than 200 kPa (30 psi) nor more than 414 kPa (60 psi) with a travel of at least 75 mm (3 in.).
- Though an inspector gauge connection is not mandatory for low-pressure boilers, it is recommended for the ability to verify the reading of the boiler gauge during operation.
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