patrickraj
Chemical
- Apr 5, 2003
- 87
We have a horizontal centrifugal pump for ammonia service. Pump is taking suction from a horizontal cylindrical tank located at 20.0 feet elevation(from tank bottom).
Pump suction pressure : 279.7 psiA
Temperature : 100°F
Sg : 0.58 4
Vapour pressure at 100°F : 212 psiA
Suction pipe : 6 " dia
Length : 30 Feet with a gate valve & 5 nos 90° bend.
I have calculated the NPSH(A) as 286 feet. But the data sheet reads only "20 + " feet. NPSH(R) indicated is 11.0 feet. NPSH(A) calculation details :
System pressure : 279.7x2.31/0.584 = 1106.4 feet
Vapour pressure : 212 x 2.31 / 0.584 = 838.6 feet.
Friction loss : 2.2 feet
Velocity head : 0.46 feet
NPSH(A) :Sys Press + Ele. +Vel Head – VP - Friction loss
NPSH(A) =1106.4 + 20+0.46 - 838.6 – 2.2
=286.0 feet
What could be the reason for the NPSH(A) indicated value of only "20 + " against the calculated value of 286 feet.
What is actual NPAH(A)
Thanks in advance.
Pump suction pressure : 279.7 psiA
Temperature : 100°F
Sg : 0.58 4
Vapour pressure at 100°F : 212 psiA
Suction pipe : 6 " dia
Length : 30 Feet with a gate valve & 5 nos 90° bend.
I have calculated the NPSH(A) as 286 feet. But the data sheet reads only "20 + " feet. NPSH(R) indicated is 11.0 feet. NPSH(A) calculation details :
System pressure : 279.7x2.31/0.584 = 1106.4 feet
Vapour pressure : 212 x 2.31 / 0.584 = 838.6 feet.
Friction loss : 2.2 feet
Velocity head : 0.46 feet
NPSH(A) :Sys Press + Ele. +Vel Head – VP - Friction loss
NPSH(A) =1106.4 + 20+0.46 - 838.6 – 2.2
=286.0 feet
What could be the reason for the NPSH(A) indicated value of only "20 + " against the calculated value of 286 feet.
What is actual NPAH(A)
Thanks in advance.