Automatic Boiler Controls Flashcards
what are 4 basic things that any control system must perform?
measure, compare, compute, correct
what does the term manipulated variable mean?
any quantity or condition that is varied by a control systems to affect the value of the controlled variable
what does the term controlled variable mean?
any quantity or condition that is measure and controlled by a control system
an example of a final control element in the three element feed system would be what?
the feed water control valve
the steady satte difference between the control point and the value of the controlled variable corresponding to the set point is called what?
offset
deviation is the instantaneous difference between the actual valley of the controlled valve and the value of the controlled variable corresponding to what?
set point
the term dead time refers to what?
the time required to transport a change from one place to another
what are 3 ways that computing and comparison can be accomplished in a pneumatic transmitter?
the nozzle and vane assembly; bellows; escapement valves
continuous changing of the controlled variable is called what?
cycling
what re the three modes of control in the automatic boiler control system?
automatic, remote manual, local manual
what are the three loops associated with the automatic boiler control system?
steam pressure control loop, airflow control loop, fuel flow control loop
what will be the position of the feed water control valve if the diaphragm ruptures?
100% Open
what is the only authoritative source of information on the boiler control system on any ship?
the manufacturer’s technical manual
what does the term supply air pressure refer to?
the compressed air that is supplies to each pneumatic unit
compressed air that goes from one pneumatic unit to another pneumatic unit is known as?
loading pressure
a general regulator automatic combustion control system on a 600 psi steam plant is designed to maintain what set point when measured from the superheater outlet?
600 - 615 psig
what is the effective loading pressure range on a General Regulator combustion control system?
3- 5 psi
what component within the general regulator combustion control system develops a demand signal to maintain the boiler at a desired standard for any boiler load?
steam pressure controller
what is the desired set point on general regulator steam pressure transmitter?
7 psi
what is the function of the high limit and low limit relays on a general regulator combustion control system?
to prevent the master demand signal from bleeding out of range on the high end or the low end of the signal range operating pressure
the output of the high limit relay is applies to what component
low limit relay
what is the function of the airflow transmitter?
measures the pressure difference across the burner opening and develops a loading signal proportional to the rate of airflow per burner
the air flow controller serves what function?
develops a loading signal to the force draft blower speed control
the airflow controller is what type of controller?
proportional plus reset
what component within the general regulator combustion control systems designed to speed up force draft blower response time?
steam flow rate relay
what component converts the fuel oil demand signal a nonlinear signal?
characterizing relay
how is the minimum fuel oil pressure set on a general regulator FO control valve?
by adjusting the spring fore in the valve with the external spring adjusting screw and locking it in place with jam nut
a blown diaphragm within the FO characterizing relay on a general regulator combustion control system will have what effect on fuel oil header pressure?
fuel oil pressure will go to maximum and cause black smoke boiler assembly
what three elements are measured within the feed water control system?
boiler drum level, steam flow and feed flow
what component within the three element feed water control system develops a pneumatic signal proportional to actual boiler water level?
drum level transmitter
what terms are used to describe the three pneumatic signals associated with the feed water control system?
drum level = supervisory signal, steam flow = demand signal, feed flow = response signal
what component within the three element feed water control system compares the steam flow signal, feed flow signal and set point signal and develops a pneumatic output signal proportional to the difference between its inputs?
steam flow/ feed flow differential relay
what is the set point adjuster set at to maintain a normal water level on the three element feed water control system?
9 psi
what type of positioner is always used in conjunction with the feed water control valve?
reverse acting
the fuel oil control valve will always fail to what position if control air pressure is lost?
minimum
the main feed pump control valve will fail to what pressure if control air pressure is lost?
maximum
the force draft blower final control element will fail in what position if control air is lost?
minimum
what is the maximum allowable rpm differential on two force draft blowers operating in parallel?
300 rpms
what system is designed to hold on final control elements in their last known position upon a loss of control air pressure?
the air lock system
what is the master air lock trip valve spring set at?
65 psig
a pressure reducing valve is installed upstream of the air lock system and maintains the control air pressure at what?
80 psig
individual final control element air lock valves are set to trip at what control air pressure?
40 psig
air lock is designed to hold for what minimum time frame IAW PMS?
10 minutes
what procedures are used to verify that each automatic boiler control component is functioning properly prior to conducting boiler flex testing?
online verification procedures (OLVs).
A boiler flex test shall be conducted in what
an up and down ramp with boiler with a load change at 70 percent in 45 seconds, within a range from 15-95 percent of boiler full power
who must witness or designate someone to ensure all boiler flex testing is conducted within PMS requirements?
engineer officer
boiler flex testing is conducted at what interval IAW PMS?
semi annually
after conducting a boiler flex up ramp or down ramp the boiler parameters must stabilize what time frame?
4 minutes
all boiler flex testing is conducted in accordance with what document?
PMS MRC
who conducts boiler flex testing?
the person assigned as the automatic boiler control tech
what NSTM contains general information on various automatic boiler control systems?
NSTM 255
who is tasked with ensuring the boiler flex up ramp or down ramp only lasts 45 seconds?
the person operating the main engine ahead throttle valve (throttle man)
the maximum signal selector selects the higher of the steam pressure signals and sends it to what component?
the steam pressure controller
what are the two inputs to the minimum signal receptor?
master demand and airflow
what is the function of the fuel air ratio relay?
provides the operator with means of adjusting the airflow signal as necessary to provide optimum combustion throughout the firing range of the boiler
the term bias refers to what?
the act of adding or subtracting from a control system signal
what are three loops associated with the automatic boiler control system?
steam pressure, airflow and fuel flow
how is biasing accomplished?
by manually adjusting the hand wheel on the compensating relay (AM station), this can only be accomplished on a 4 way compensating relay
the compressed air that goes from a pneumatic unit to a motor operator of a final control element is defined as?
control pressure
what component cuts down the lag time casual by forced draft blower inertia?
steam flow relay
who must accomplish adjustment or repair of automatic boiler controls?
only authorized and qualified individuals
the interval of time between the start of a response and its completion is termed what?
lag time
a closed loop system gives a comparison with the desired condition by using?
feedback
output of an escapement valve is determined by?
position of the valve seats
on a nozzle and flapper assembly, what’d device is used to restrict the flow through the nozzle?
flapper
an orifice plate, flow nozzle, thermometer bulb, and air registers are all examples of what?
primary elements
the time interval by which rate action advances the effect of proportional position action is?
rate time
an uncontrolled oscillation of a controlled variable is termed?
hunting
on nozzle and flapper assembly, when the flow through the nozzle is decreased, the output will?
increase
a desired restriction in the path of the flow is at?
primary element
the automatic control system compares the measure valve with?
the desired value
what integral action of a controller will bring it back into balance, after a load change, at set point?
reset
boiler flex testing is measure in how many levels IAW PMS?
five
what boiler flex level is considered optimum for plant operation?
level one
is it allowable to conduct ETT drills on boiler that cannot conduct a satisfactory level three or higher boiler flex test?
never, ETT drills shall only be conducted on boilers that have achieved a level three or higher flex test
what effect will a failure of an airflow transmitter have on an operating steam plant?
fuel oil header pressure will decrease to minimum
when performing master light off checks what is the reason for conducting the EOP CTRM on the automatic boiler control system?
to verify that the airflow transmitter and minimum signal selector are functioning properly
what automatic boiler component must be adjusted prior to conducting boiler soot blow?
the fuel air ratio relay must be adjusted to increase windbag pressure IAW EOSS
what is meant by the term two knob centric when dealing with automatic boiler controls?
fuel and air controls are being manipulated by remove manual means
during a white smoke condition on an operating boiler, what must never be adjusted?
fuel oil header pressure
what action must be taken if a controlled variable oscillates about the set point at high frequency?
reduce the controller sensitivity
what is the most common cause of a control valve or actuator not responding to a position input a signal?
mechanical preference
the primary function of the automatic feed water control system is to maintain boiler water level within set point ?
normal with a maximum deviation of + - one inch at all boiler loads
