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# Steam Math Question

Member Posts: 12
In a steam generating plant, the feedwater pumps are of the steam driven reciprocating duplex type. Steam at boiler pressure, 100lbs./sq.in., is used to drive these pumps. The pumps are designed to work against a head of 150 lbs/sq.in., and the steam pistons have a diameter of 31/2 inches.

Under these above conditions, the water plungers should have a diameter, in inches, MOST NEARLY equal to:

A) 3.85"

B) 3.26"

C) 2.25"

D) 2.86"

I know thw correct answer is C)  2.86", but I was wondering if anyone knew the formula on how to get the answer? Thanks

• Member Posts: 604
edited December 2011
Area times pressure

The steam cylinder will exert a force of 100psi x 3.14 x 3.5" x 3.5" / 4 = 962 lbs

(pressure times piston area)  where area = pi times diameter squared divided by 4

The same force will be applied to the water cylinder:

150psi x 3.14 x D squared / 4 = 962

117.75 D squared = 962

D squared = 962 / 117.75 = 8.17

Square root of 8.17 = 2.86

So diameter of water piston is 2.86 inches
• Member Posts: 12
Steam Math Question

WOW!!!   Thanks Mike, I'll have another one for you tomorrow
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