Fittings & Mountings
Essential boiler fittings including gauge glass, try cocks, pressure gauges, and water column.
Gauge Glass (Water Level Indicator)
The gauge glass provides a visible indication of the water level inside the boiler. It is the primary means of monitoring water level during operation.
- Shows actual water level in the boiler
- Must be kept clean and readable at all times
- Blow down the gauge glass regularly to verify accuracy
- A plugged gauge glass can give a FALSE water level reading
- Replace cracked or discolored glass immediately
Never trust the gauge glass alone — verify with try cocks regularly.
Try Cocks
Try cocks are small valves mounted on the water column that provide an independent method to verify water level.
- Three try cocks are required on high-pressure boilers
- Top try cock: should show steam (above water line)
- Middle try cock: should show a mix of steam and water (at normal water level)
- Bottom try cock: should show water (below water line)
- Used to verify gauge glass readings
If all three try cocks show steam, the water level is dangerously low.
Pressure Gauge
The pressure gauge indicates the steam pressure inside the boiler.
- Bourdon tube type is most common
- Connected to the boiler through a siphon or pigtail to protect from direct steam
- Dial must show MAWP marked with a red pointer or line
- Must be tested and calibrated regularly
- Range should be approximately 1.5–2x the MAWP
Water Column
The water column is a vertical chamber connected to the boiler that houses the gauge glass and try cocks.
- Provides a calm area for accurate water level readings
- Must be blown down regularly to remove sediment
- Cross-connections to the boiler must be kept clear
- LWCO is typically mounted on or connected to the water column
Fusible Plug
A fusible plug is a safety device with a low-melting-point core that releases steam if water level drops below a safe point.
- Tin or Babbitt metal core melts at approximately 450°F
- Located at the lowest permissible water level
- Releases steam/water as a warning of dangerously low water
- Must be inspected and replaced periodically
- Required on some firetube boilers