GFES Question

[theedge56]

I am trying to figure this question out:

TOPIC: 191002
KNOWLEDGE: K1.10 [2.3/2.5]
QID: P2109 (B2109)
A centrifugal pump is taking suction from the bottom of a vented cylindrical storage tank that
contains 100,000 gallons of water at 60F. A pressure gauge at the inlet to the pump indicates 40
psig. Over the next several days storage tank temperature increases to 90F with no change in tank
water level and no change in head loss in the pump suction line.
Which one of the following is the current pressure at the inlet to the pump?
A. 39.8 psig
B. 37.4 psig
C. 34.6 psig
D. 31.2 psig
ANSWER: A.

How is the conclusion reached?

[Nuclear Renaissance]

static head = density x g x height of column of water

rearranged,

height of column of water = static head / (density x g)

since tank level remains constant (and g cancels out),

static head at 60 / density at 60 = static head at 90 / density at 90.

thus

static head at 90 = static head at 60 x (density at 90 / density at 60)

[Fermi2]

He's right!

[theedge56]

Thanks