Steam and Hot Water Boiler Controls 080307c Flashcards
What is the maximum allowable pressure for a low pressure steam boiler?
15 psig
What is the function of the differential pressure switch (DOPS)?
Cuts off the fuel supply when the steam pressure reaches an operating set point
The DOPS is a pressure sensing switch
What is the function of the high limit pressure switch in a steam boiler?
Cuts off fuel supply to prevent steam pressure from exceeding the maximum allowable pressure (15 psig)
The loop of a pigtail should be set at ___° to the face of any pressure controls with mercury switches in them
90
A flow switch is required on what kind of boiler?
Low mass over 400MBH
A low water cut off is required on what kind of boiler?
High mass over 400MBH
Many different types of sensing elements can be found on aquastats, but most common one is what?
Liquid bulb with capillary tube
An alternate method of installation of a sensing bulb is what?
Immersion well (thermal well)
A high limit switch is what kind of switch?
Single pole single throw break on temp rise
What is the function of a safety limit control on a hot water boiler?
Prevent water temperature from exceeding the maximum allowable temperature (250°F)
What is the maximum allowable temperature in a hot water boiler?
121°C (250°F)
Once a limit control has closed the gas valve, the control will not allow the boiler to fire until what happens?
The control has been reset manually
What is considered the final form of boiler protection?
Safety relief valve
What is the function of the safety relief valve on a steam boiler system?
It safeguards the boiler from over pressuring
What 2 pressure controls must a steam boiler have?
Differential operating pressure switch (DOPS)
High limit pressure switch
What 2 controls must a hot water boiler have?
Operating temperature switch
High limit temperature control switch
Boiler maintenance may be as little as how often?
Yearly
If a float chamber type control seems stuck in the up position after us has been drained, what may be the solution?
Tap on it
High oxygen content in a boiler system may cause what?
Will corrode steel components in the system and may result in boiler failure
How much slope should be on a horizontal vent connector?
Not less than 1/4” per foot
What is the sequence of operations for a an electrical ladder diagram?
Power - Switch - Load
Where is a reduced principal backflow preventer placed on a boiler system?
On the boiler feed water line immediately upstream of the boiler feed water valve
Operating controls have what kind of differential?
Adjustable
Safety controls have what kind of differential?
Fixed
