ASME CSD-1-2009 pdf – Controls and Safety Devices for Automatically Fired Boilers.
CW450 Requirements for Operating and Safety Controls for Electrically Heated Boilers
Electric resistance and electrode boilers shall have a boiler feed control system that shall maintain the operating level in steam boilers and operating water pressure on hot-water boilers. Where uncovering of the electrical element can lead to an unsafe condition, the boiler shall be provided with low-water fuel cutoff(s) in accordance with Part CW. Boiler feed control and low- water fuel cutoff may he common to one control. In the case of electrode-type boilers, where the reduction in water level provides a self-limiting control on input, low-water fuel cut-off controls are not required.
CW210 Requirements for Flow or Temperature- Sensing Devices for Forced Circulation Boilers
(a) In lieu of the requirements for low-water fuel cutoffs in CW-100, a water tube or coil-type boiler, requiring forced circulation to prevent overheating and failure of the tubes or coils, shall have an accepted safety control to prevent burner operation at a flow rate inadequate to protect the boiler unit against overheating, at all allowable firing rates. This safety control shall shut down the burner and prevent restarting until an adequate flow is restored. Positive means shall he provided to determine during testing that the accepted safety control has functioned upon an inadequate flow condition. The positive means shall enable the accepted safety control to remain in the running safety lock circuitry during testing. The safety control must be automatically restored to service after completion of system testing.
(1,) When there is a definitive waterline, a low-water fuel cutoff complying with the applicable portions of CW-100 shall be provided in addition to the sensing device required in (a) above. Functioning of the low- water fuel cutoff shall cause a safety shutdown and lOCkOUt.
CW-310 Requirements for Pressure Controls for Steam Boilers
(a) Each boiler pressure control shall conform to UL 353, Standard for Limit Controls, and shall be accepted by a nationally recognized testing agency.
(b) Each automatically fired steam boiler or system of commonly connected steam boilers shall have at least one steam pressure control device that will shut off the fuel supply to each boiler or system of commonly connected boilers when the steam pressure reaches a preset maximum operating pressure. This requirement does not preclude the use of additional operating control devices where required.
(c) In addition to the pressure control required in (b) above, each individual automatically fired steam boiler shall have a high steam pressure limit control that will prevent generation of steam pressure greater than the maximum allowable working pressure. Functioning of this control shall cause safety shutdown and lockout. The manual reset may be incorporated in the pressure limit control. Where the reset device is separate from the pressure limit control, a means shall be provided to indicate actuation of the pressure limit control. Each limit and operating control shall have its own sensing element and operating switch.
EXCEPTION: Lockout is not required for boiler units installed in residences, as defined by the authority having jurisdiction.
(d) A pressure limit control of the automatic or manual reset type shall be electrically connected in accordance with CE-11O(i).
(e) No shutoff valve of any type shall be placed in the steam pressure connection between the boiler and the high-pressure limit control device and steam pressure control device or between the boiler and steam pressure control device.
f) Each pressure control device shall be protected with a siphon, or equivalent means of maintaining a water seal, that will prevent steam from entering the control. The minimum size of a siphon shall be NPS 1/4• Tubing suitable for the temperatures and pressures involved, with an inside diameter at least equal to standard pipe sizes, may be substituted for pipe. When a control incorporating a mercury switch is mounted on the siphon, the loop of the siphon shall be in a plane that is 90 deg (1.57 rad) from the plane of the mercury switch.
(g) Steam pressure supply connections to a single pressure control using pipe of nonferrous material shall not be less than NPS 1/4 for lengths up to and including 5 ft (1.5 m) and not less than NPS ‘2 for lengths over
5 ft (1.5 m). Tubing suitable for the temperatures and pressures involved, having an inside diameter at least equal to that of standard pipe, may be substituted for pipe.