Answer / pradeepa

NPSH is net positive suction head of a pump. For
centrifugal pumps, it is calculated as follows:

NPSHa = Atm. pr. + static head - vapour pressure - pressure
loss in the suction piping - pressure loss due to the
suction strainer.

Answer / p.manikandan

NPSH is the acronym of Net Positive Suction Head, there r 2
NPSH one is NPSH(a) and NPSH(r) i.e., NPSH available and
required. Always NPSH(a) should be higher than the NPSH(r)
this NPSH(R) will be determined my the pump manufacturer
itself.

TO calculate NPSH(a)
NPSHa = Atm. pr.acting on the liquid + static head - vapour
pressure of the liquid- pressure
loss in the suction piping - pressure loss due to the
suction strainer.

Answer / karthick

net positive suction head is one of the design criteria in
centrifugal pump.it determines the intake pressure of the
fluid.the pressure at the suction head should be sufficient
enough to overcome the losses.

Answer / jimmy jacob

The definition of NPSHa is very simple. We can calculate
NPSH all we have to do is to take the sum of the static
head plus the surface pressure head and then subtract it
from the vapor pressure of the product (whatever) along
with the frictional losses in the piping, valves & fittings

Answer / saravanan

NPSH is Net Positive Suction Head.. As the name indicates
it is the Positive suction head that should be necessarily
available at suction to prevent the liquid from boil up due
the vapor pressure of the liquid at pumping temperature. It
is also said as the Head necessary at the suction to over
come the vapor pressure of the liquid at pumping
temperature.
Liquid if pumped at low pressure & high temperature (close
to boiling point) nullifies vapor pressure and cavitates.
NPSH available should always be greater than NPSH required
defined by the pump vendor (NPSH R is function of the pump
impeller geometry) to get improved performance.

NPSH available = Suction Pressure - Vapor Pressure + Static
Head - Frictional loss across the suction line.

Since the velocity at the suction is minimum, dynamic head
can be ignored. Hence the only deciding factor is Static
Head, Suction pressure & Operating Temperature..

Higher the static head, higher is the suction pressure &
lower is the pumping temperature better would be the NPSH
avaialble at the impeller eye.

Answer / t.nandakumar

NPSH means the net positive suction head.There are two
types of NPSH - NPSH available & NPSH required.

NPSH available = suction pressure + suction static head -
pressure drop in suction piping & fittings - vapour
pressure drop- presssure drop in section strainer.

NPSH required - NPSH specified by the pump supplied which
shall be atleast less than NPSH available by difference of
one.

Answer / raguvir

Its defined as positive pressure available above the vapour
pressure

Answer / nasser khattab

Given:
• Atmospheric pressure = 14.7 psi
• Gage pressure =the tank is at sea level and open to atmospheric pressure.
• Liquid level above pump centerline = 5 feet
• Piping = a total of 10 feet of 2 inch pipe plus one 90° long radius screwed elbow.
• Pumping =100 gpm. 68°F. Fresh water with a specific gravity of one (1).
• Vapor pressure of 68°F. Water = 0.27 psi from the vapor chart.
• Specific gravity = 1
• NPSHR (net positive suction head required, from the pump curve at 100 gpm) = 9 feet

Now for the calculations:
NPSHA = Atmospheric pressure(converted to head) + static head + surface pressure head - vapor pressure of your product - loss in the piping, valves and fittings
• Static head = 5 feet
• Atmospheric pressure = pressure x 2.31/sg. = 14.7 x 2.31/1 = 34 feet absolute
• Gage pressure = 0
• Vapor pressure of 68°F. water converted to head = pressure x 2.31/sg = 0.27 x 2.31/1 = 0.62 feet
• Looking at the friction charts:
o 100 gpm flowing through 2 inch pipe shows a loss of 17.4 feet for each 100 feet of pipe or 17.4/10 = 1.74 feet of head loss in the piping
o The K factor for one 2 inch elbow is 0.4 x 1.42 = 0.6 feet
• Adding these numbers together, 1.74 + 0.6 = a total of 2.34 feet friction loss in the pipe and fitting.
NPSHA (net positive suction head available) = 34 + 5 + 0 - 0.62 - 2.34 = 36.04 feet
The pump required 9 feet of head at 100 gpm. And we have 36.04 feet so we have plenty to spare.

Answer / m.s.suresh

NPSH is the minimum suction conditions required to pump a
liquid with out cavitation.
To mee the above requirments
NPSH a > NPSHr (minimum NPSHa should be 3% > NPSHa)

Answer / yasir shfique

It is the positive pressure at pump suction above the
vapour pressure at pump temperature.

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