Boiler Pressure Control Quiz
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Questions and Answers

What is the major difference in the primary sensing elements between steam boilers and hot water boilers?

  • Steam boilers require temperature-sensitive sensors, while hot water boilers require flow rate sensors.
  • Steam boilers require temperature-sensitive sensors, while hot water boilers require pressure-sensitive sensors.
  • Steam boilers require flow rate sensors, while hot water boilers require pressure-sensitive sensors.
  • Steam boilers require pressure-sensitive sensors, while hot water boilers require temperature-sensitive sensors. (correct)

In two-position firing rate control, what is the cut-in point for the burner in the case of steam boilers?

  • 50 kPa
  • 35 kPa (correct)
  • 100 kPa
  • 70 kPa

What is the primary manipulated variable in steam boiler control systems?

  • Steam pressure
  • Airflow
  • Firing rate (correct)
  • Fuel flow

Why is two-position control only used in smaller capacity boilers?

<p>Energy losses due to frequent cycling have less economic impact for small capacity boiler plants than for large capacity plants. (A)</p> Signup and view all the answers

What happens when a hot water boiler continues to fire at an excessive rate?

<p>The boiler will produce supersaturated hot water and over-pressurize due to liquid expansion. (A)</p> Signup and view all the answers

What is the primary focus of this chapter?

<p>Boiler-firing circuits (D)</p> Signup and view all the answers

Which code most suitably addresses automatic firing rate controls for boilers?

<p>ASME CSD-1 Controls and Safety Devices for Automatically Fired Boilers (C)</p> Signup and view all the answers

What is the purpose of firing rate controls in boilers?

<p>To increase boiler efficiency (C)</p> Signup and view all the answers

In the event of an operating control failure, what must high limit controls be able to do?

<p>Shut off the burner to prevent unsafe operating conditions (B)</p> Signup and view all the answers

What must the energy output of a boiler always equal?

<p>The energy demand (A)</p> Signup and view all the answers

What is the purpose of high-low firing rate control in a boiler?

<p>To maintain finer control of the boiler steam pressure or temperature (D)</p> Signup and view all the answers

Why do high-low boilers require two operating pressure controls (pressuretrol) instead of one?

<p>To maintain the high-fire and low-fire burner circuits separately (C)</p> Signup and view all the answers

What happens when the low-fire burner circuitry is energized in a high-low boiler?

<p>It remains energized until the boiler pressure reaches a certain level (A)</p> Signup and view all the answers

In a multi-position firing rate control, what happens when the load demand increases?

<p>The low-fire burner cannot satisfy the load demand and the boiler pressure continues to drop (B)</p> Signup and view all the answers

What makes fully modulating firing rate control different from high-low and multi-position firing rate control?

<p>It can operate at any one of an infinite number of firing rates between high-fire and low-fire (A)</p> Signup and view all the answers

What causes mercury switches to occasionally fail?

<p>Oxygen entering through small cracks and oxidizing the mercury (C)</p> Signup and view all the answers

What type of switches are used instead of mercury switches?

<p>Purely mechanical switches with a pressure capsule (B)</p> Signup and view all the answers

How does the high-pressure cut-off (HPCO) differ from the operating pressure control?

<p>It has a manual reset button (C)</p> Signup and view all the answers

What is the purpose of the high-temperature limit control for hot water boilers?

<p>To prevent the water temperature from exceeding the maximum allowable water temperature (D)</p> Signup and view all the answers

How is the high-temperature cut-off (HTCO) different from the operating temperature control?

<p>It has a higher setting than the operating temperature control (A)</p> Signup and view all the answers

What is the purpose of limiting the boiler to low-fire when starting up a cold boiler with fully modulating firing rate control?

<p>To prevent uneven thermal expansion and excessive stress on the boiler (B)</p> Signup and view all the answers

What type of control devices do hot water boilers with fully modulating firing rate control use to control the firing rate?

<p>Variable resistance temperature-actuated sensors (A)</p> Signup and view all the answers

What type of switches are used as operating pressure controls, low fire controls, and high-pressure cut-offs in two-position (on-off) steam boilers?

<p>Pressure-actuated two-position single pole, single throw switches (D)</p> Signup and view all the answers

What is the purpose of the high-pressure cut-off control in hot water boilers with fully modulating firing rate control?

<p>To prevent generation of steam pressure above the maximum allowable working pressure (C)</p> Signup and view all the answers

What is the purpose of the pressuretrol in a steam boiler equipped for fully modulating firing rate control?

<p>To position a modulating motor that drives the combustion air damper and the firing rate control valve (D)</p> Signup and view all the answers

What is the purpose of the manual reset button on the high-temperature cut-off (HTCO)?

<p>To lock the switch in the open position when activated (A)</p> Signup and view all the answers

What is the purpose of a modulating pressure control in steam boilers with fully modulating burners?

<p>To control how closely the boiler pressure tracks the set point (D)</p> Signup and view all the answers

In hot water boilers with fully modulating burners, what is the purpose of a modulating temperature control?

<p>To control how closely the boiler pressure tracks the set point (C)</p> Signup and view all the answers

What is the function of a modulating motor in electrical control systems for boilers?

<p>To position dampers and valves in electrical control systems (C)</p> Signup and view all the answers

Why might some larger boilers use two modulating motors?

<p>To control both air and fuel flow (C)</p> Signup and view all the answers
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