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Water Level Controls and Devices

Print Date: 2/19/2018 10:12:43 AM

Description and Overview
Water level controls and devices include:

A water column is used on a steam boiler to reduce the turbulence and fluctuation of the water level so the gage glass can provide a steady, accurate water level reading. The use of a water column is not mandatory.

A level indicator, whether it be a gage glass, indirect sensing method, or independent remote, is used on a steam boiler to provide a water level reading. A gage glass is the most common form of level indicator found on steam boilers. Depending upon ASME BPV Code requirements, the gage glass can be a round glass "window" known as a bull's-eye, a glass tube with a circular cross-section, or a flat glass assembly held in a special frame. An indirect sensing method, as allowed in ASME BPV Code Section IV, could be in the form of a floating magnet which causes colored "flags" external to the mechanism to flip over, indicating the water level. If an indirect sensing method is used, an operable gage glass must also be installed. An independent remote level indicator, as allowed in ASME BPV Code Section I, could include fiber-optic cables, video camera, electronic representation on a computer monitor, and magnetic devices. Section I has specific requirements which must be followed when using these types of indicators.

A low-water fuel cutoff is used on both steam and hot water boilers to shut off the fuel or source of heat when the water drops below a predetermined, safe operating level. The most common type of low water fuel cutoff is a float inside a chamber. The float mechanism actuates an electrical switch when the float reaches a preset level. Another popular form of low-water fuel cutoff is called a probe type. This variation uses rod-like electrical probes inserted into the boiler or in an external chamber. When the probes are in contact with the water, an electrical circuit is completed using the water as a conductor. If the probes lose contact with the water, the electrical circuit is opened. Some low-water fuel cutoffs have a manual reset device built in. The purpose of this is to alert the operator that the low-water fuel cutoff has activated. The operator should then look for the problem that caused the low-water condition before resetting the device and restarting the boiler.

A feedwater regulator can be found in different forms. This guide will address only those most commonly used on small- to medium-sized boilers. The feedwater regulator is essentially a valve installed in conjunction with the boiler to ensure the water is maintained at the desired level. The valve can be opened either mechanically by direct actuation of a float, electrically, or pneumatically. Many times the feedwater regulator is installed as a mechanically integral component of the low-water fuel cutoff or it may be controlled by a signal from a low-water fuel cutoff.

A pump controller is an electrical switch used for controlling a feed pump on a steam boiler. While this may seem to be similar to one of the variations of a feedwater regulator, it does serve a different purpose.

All the devices listed above must be constructed and rated for the pressure and temperature applicable to the installation.


Common Observations and Problems
All water level controls and devices must operate as designed in order to perform their required tasks. Different types of problems can prevent normal operation:

While inspecting low-pressure or high-pressure boilers, the inspector will be observing water level controls and devices. The inspector must take the time necessary to completely evaluate the condition and operational effectiveness of these controls and devices. The inspector should consider:

Miscellaneous Information