Valves Flashcards
Which one of the following describes the function of a safety valve?
A. Provide overpressure protection to limit the internal pressure in vessels.
B. Control pressure in a system to maintain optimum operational conditions.
C. Sound a warning by lifting at a predetermined value slightly higher than operating pressure.
D. Modulate open as necessary to maintain system pressure and/or temperature within normal limits.
Provide overpressure protection to limit the internal pressure in vessels.
A vertical safety valve has a compressed spring assembly that is applying 1,200 lbf to the top of the
valve disk in opposition to system pressure. System pressure is being exerted on the underside of the
valve disk that is 3 inches in diameter.
Which one of the following is the approximate system pressure at which the safety valve will open?
A. 44 psig
B. 64 psig
C. 128 psig
D. 170 psig
170 psig
A vertical safety valve with a 3-inch diameter disk has a spring applying 1,000 lbf to the top of the
valve disk in opposition to system pressure. Which one of the following is the approximate system
pressure at which the safety valve will begin to open?
A. 35 psig
B. 111 psig
C. 141 psig
D. 444 psig
141 psig
Refer to the drawing of a typical safety valve (see figure below).
The component indicated by the solid arrow is used when necessary to manually…
A. ratchet open the safety valve.
B. pop open the safety valve.
C. gag shut the safety valve.
D. determine the position of the safety valve.
pop open the safety valve.
A vertical safety valve has a compressed spring assembly that is applying 2,500 lbf to the top of the
valve disk in opposition to system pressure. System pressure is being exerted on the underside of the
valve disk that is 5 inches in diameter.
Which one of the following is the approximate system pressure at which the safety valve will open?
A. 32 psig
B. 127 psig
C. 159 psig
D. 500 psig
127 psig
A vertical safety valve with a 2-inch diameter disk has a compressed spring applying 2,400 lbf to the
top of the valve disk in opposition to system pressure. Which one of the following is the approximate
system pressure at which the safety valve will open?
A. 95 psig
B. 191 psig
C. 382 psig
D. 764 psig
764 psig
Given the following specifications for a main steam safety valve (MSSV):
Setpoint pressure (MSSV starts to open) = 1,200 psia
Maximum pressure (MSSV will be fully open) = 1,230 psia
Reseat pressure (MSSV will be fully closed) = 1,140 psia
Which one of the following is the percent blowdown for the MSSV?
A. 2.5 percent
B. 5.0 percent
C. 7.5 percent
D. 33.3 percent
5.0 percent
A completely full water storage tank is being hydrostatically tested to 100 psig using a positive
displacement pump (PDP) with a smooth and constant discharge flow rate of 10 gpm. The tank is
protected by a safety valve and a relief valve; both valves discharge to the atmosphere. Each valve
has an opening setpoint of 105 psig and a maximum rated discharge flow rate of 6 gpm. The PDP is
inadvertently left running when tank pressure reaches 100 psig.
With the PDP still running, tank pressure will stabilize __________ 105 psig; and the greater mass
flow rate will be coming from the __________ valve.
A. at; safety
B. above; safety
C. at; relief
D. above; relief
above; safety
Given the following pressure specifications for a safety relief valve (SRV):
Setpoint pressure (SRV will start to open) = 1,200 psia
Maximum pressure (SRV will be fully open) = 1,242 psia
Reseat pressure (SRV will be fully closed) = 1,152 psia
Which one of the following is the percent accumulation for the SRV?
A. 2.5 percent
B. 3.0 percent
C. 3.5 percent
D. 4.0 percent
3.5 percent
A completely full water storage tank is being hydrostatically tested to 200 psig using a positive
displacement pump (PDP) with a smooth and constant discharge flow rate of 8 gpm. The tank is
protected by a relief valve and a safety valve; both valves discharge to the atmosphere. Each valve
has an opening setpoint of 205 psig and a maximum rated discharge flow rate of 6 gpm. The PDP is
inadvertently left running when tank pressure reaches 200 psig.
When conditions stabilize with the PDP still running, the relief valve will be __________ open; and
the safety valve will be discharging a flow rate of approximately __________ to the atmosphere.
A. partially; 6 gpm
B. partially; 2 gpm
C. fully; 6 gpm
D. fully; 2 gpm
partially; 6 gpm
Refer to the drawing of two identical water storage tanks (see figure below). Tank A is protected by a
relief valve and Tank B is protected by a safety valve. Each valve has an opening setpoint of 205 psig
and a maximum rated discharge flow rate of 8 gpm.
The tanks are being hydrostatically tested to 200 psig. Each tank is being supplied with a smooth and
constant flow rate of 2 gpm from separate positive displacement pumps (PDPs). Both PDPs are
inadvertently left running when tank pressures reach 200 psig.
With the PDPs running continuously, what will be the resulting status of the relief and safety valves?
Relief Valve Status
Safety Valve Status
A. Partially open Partially open
B. Partially open Cycling between fully
open and fully closed
C. Cycling between fully
open and fully closed Partially open
D. Cycling between fully
open and fully closed
Cycling between fully
open and fully closed
Partially open Cycling between fully
open and fully closed
A completely full water storage tank is being hydrostatically tested to 200 psig using a positive
displacement pump (PDP) with a smooth and constant discharge flow rate of 8 gpm. The tank is
protected by a relief valve and a safety valve that both discharge to the atmosphere. The valves have
the following characteristics:
* The relief valve opening setpoint is 200 psig with an accumulation of 5 percent.
* The safety valve opening setpoint is 240 psig with a blowdown of 5 percent.
* Both valves have a maximum discharge flow rate of 6 gpm.
The PDP is inadvertently left running when tank pressure reaches 200 psig.
When conditions stabilize with the PDP still running, the relief valve will be __________ open; and
the safety valve will be discharging a flow rate of approximately __________ to the atmosphere.
A. partially; 6 gpm
B. partially; 2 gpm
C. fully; 6 gpm
D. fully; 2 gpm
fully; 2 gpm
A main steam system uses a combination of safety valves and relief valves for overpressure protection.
Which one of the following describes a major design consideration for installing both types of valves
in the same system?
A. The safety valves are installed to prevent chattering of the relief valves during normal power
operation.
B. The safety valves are installed to prevent unnecessary opening of the relief valves during a steam
pressure transient.
C. The relief valves are installed to prevent chattering of the safety valves during normal power
operation.
D. The relief valves are installed to prevent unnecessary opening of the safety valves during a steam
pressure transient.
The relief valves are installed to prevent unnecessary opening of the safety valves during a steam
pressure transient.
A completely full water storage tank is being hydrostatically tested to 200 psig using a positive
displacement pump (PDP) with a smooth and constant discharge flow rate of 8 gpm. The tank is
protected by a relief valve and a safety valve that both discharge to the atmosphere. The valves have
the following characteristics:
* The relief valve opening setpoint is 220 psig with an accumulation of 5 percent.
* The safety valve opening setpoint is 260 psig with a blowdown of 5 percent.
* Both valves have a maximum discharge flow rate of 6 gpm.
The PDP is inadvertently left running when tank pressure reaches 200 psig.
After a few minutes with the PDP still running, the relief valve will be discharging a flow rate of
approximately __________; and the safety valve will be __________.
A. 2 gpm; partially open
B. 6 gpm; partially open
C. 2 gpm; cycling between fully open and fully closed
D. 6 gpm; cycling between fully open and fully closed
6 gpm; cycling between fully open and fully closed
The primary purpose of a pressure relief valve is to…
A. reduce system energy.
B. reduce system pressure.
C. maintain system integrity.
D. maintain system mass.
maintain system integrity.
The difference between the setpoint pressure at which a safety valve opens and the pressure at which it
closes is called…
A. blowdown.
B. accumulation.
C. setpoint tolerance.
D. setpoint deviation.
blowdown
The difference between the setpoint pressure at which a relief valve begins to open and the pressure at
which it is fully open is called…
A. setpoint deviation.
B. setpoint tolerance.
C. accumulation.
D. blowdown.
accumulation
Which one of the following is a difference between a typical relief valve and a typical safety valve?
A. The actuator closing spring on a relief valve is in a compressed state whereas the actuator closing
spring on a safety valve acts in tension.
B. A relief valve gradually opens as pressure increases above the setpoint pressure whereas a safety
valve pops open at the setpoint pressure.
C. Relief valves are capable of being gagged whereas safety valves are not.
D. The blowdown of a relief valve is greater than the blowdown of a safety valve.
A relief valve gradually opens as pressure increases above the setpoint pressure whereas a safety
valve pops open at the setpoint pressure.
Refer to the drawing of two identical pressure vessels with identical relief valve protection (see figure
below).
Both vessels have been pressurized to 50 psig and then isolated. Vessel A is completely filled with
water at 150°F. Vessel B is in a saturated condition with one-half steam (100 percent quality) and
one-half water (0 percent quality) by volume.
If both relief valves fully open simultaneously, the faster pressure reduction will occur in vessel
__________; and if both relief valves close at 40 psig, the greater mass loss will have occurred in
vessel __________.
A. A; A
B. A; B
C. B; A
D. B; B
A; B
Water storage tanks A and B are identical except that tank A receives overpressure protection from a
relief valve, whereas tank B uses a safety valve. The relief valve and safety valve have the same
pressure setpoints and design flow rates.
Water is continuously added to each tank at the same rate (50 percent of the design flow rate of the
relief and safety valves). After the tanks are completely full, tank A pressure will __________; and
tank B pressure will __________.
A. fluctuate within a few percent of the pressure setpoint; stabilize slightly above the pressure
setpoint
B. fluctuate within a few percent of the pressure setpoint; fluctuate within a few percent of the
pressure setpoint
C. stabilize slightly above the pressure setpoint; stabilize slightly above the pressure setpoint
D. stabilize slightly above the pressure setpoint; fluctuate within a few percent of the pressure
setpoint
stabilize slightly above the pressure setpoint; fluctuate within a few percent of the pressure
setpoint
Vessels A and B are identical except that vessel A receives overpressure protection from an installed
safety valve. Vessel B has an installed relief valve. The safety and relief valves have the same
pressure setpoint and design flow rate.
Water is continuously added to each vessel at the same rate (50 percent of the design flow rate of the
safety and relief valves). After vessel pressure reaches the setpoint for each valve, vessel A pressure
will __________; and vessel B pressure will __________.
A. stabilize slightly above the pressure setpoint; stabilize slightly above the pressure setpoint
B. stabilize slightly above the pressure setpoint; fluctuate within a few percent of the pressure
setpoint
C. fluctuate within a few percent of the pressure setpoint; stabilize slightly above the pressure
setpoint
D. fluctuate within a few percent of the pressure setpoint; fluctuate within a few percent of the
pressure setpoint
fluctuate within a few percent of the pressure setpoint; stabilize slightly above the pressure
setpoint
Refer to the drawing of two identical pressure vessels with identical relief valve protection (see figure
below).
Vessel A is completely filled with subcooled water at 80°F and vessel B is in a saturated, two-phase
condition. Both vessels are currently pressurized to 50 psig and isolated.
If both relief valves fully open simultaneously, the faster pressure reduction will initially occur in
vessel _____; and the faster mass loss will initially occur in vessel_____.
A. A; A
B. A; B
C. B; A
D. B; B
A; A
A completely full water storage tank is being hydrostatically tested to 200 psig using a positive
displacement pump (PDP) with a smooth and constant discharge flow rate of 6 gpm. The tank is
protected by two relief valves that discharge to the atmosphere. The relief valves have the following
characteristics:
* Relief valve A opening setpoint is 200 psig with an accumulation of 1.5 percent.
* Relief valve B opening setpoint is 200 psig with an accumulation of 3.0 percent.
* Each valve has linear flow rate characteristics and a maximum discharge flow rate of 6 gpm.
The PDP is inadvertently left running when tank pressure reaches 200 psig.
With the PDP running continuously, what will be the discharge flow rates of the relief valves when
tank pressure stabilizes?
Relief
Valve A
Relief
Valve B
A. 1 gpm 5 gpm
B. 2 gpm 4 gpm
C. 3 gpm 3 gpm
D. 4 gpm 2 gpm
4 gpm 2 gpm
A completely full water tank is being hydrostatically tested to 180 psig using a positive displacement
pump (PDP) with a smooth and constant discharge flow rate of 6 gpm. The tank is protected by two
relief valves that discharge to the atmosphere. The relief valves have the following characteristics:
* Relief valve A opening setpoint is 180 psig with an accumulation of 5 percent.
* Relief valve B opening setpoint is 200 psig with an accumulation of 5 percent.
* Each relief valve has linear flow rate characteristics and a maximum flow rate of 4 gpm.
The PDP is inadvertently left running when tank pressure reaches 180 psig.
With the PDP still running, at what pressure will the tank stabilize?
A. 190 psig
B. 195 psig
C. 205 psig
D. 210 psig
205 psig