NPSHr

Net Positive Suction Head Required

All pumps have requirements to their performance, and no pump can perform well if you can't meet it's needs.

Below is part of the Cornell® 6NHTB-19 Pump Curve with a colored over-lay for this discussion.

NPSH REQUIRED is found at the top of the curves in FT.

What does this mean?

For this pump, running at 2100 RPM with its horsepower requirements met, you can pick a flow rate and easily find its NPSH REQUIRED.

1500 GPM = 5.5 FT.
2000 GPM = 8 FT.
2500 GPM = 11 FT.
3000 GPM = 17 FT.

Net Positive Suction Head Required is the required feet of head going into the back of the pump for it to function properly and achieve your desired flow rate.

Easy signs your pump's NPSHR is NOT met: 

• The pump is shaking
• It sounds like you have rocks going through your pump
• Gauges and Valves are falling off
• The unit is vibrating
• The tongue's jack is sunken into the ground from vibration
• Your gauges are broken
• Your suction cover shows physical damage of gouging and wash-out
• Your impeller shows physical damage of gouging and wash-out

CAUTION! Your Pump is Cavitating! 
More about cavitation: http://www.engineersedge.com/pumps/cavitation.htm



MEETING NPSH REQUIRED AT THE SITE:

Atmospheric Pressure – Friction Loss in Intake Hose – NPSHr of Pump = Static Suction Lift

• Static Suction Lift tells us the maximum distance from the top of the water to the center of the pump's impeller we can operate within without causing cavitation.  The pump needs to be primed, but not fed with another pump within this distance.
• Atmospheric Pressure is the force of air pressing down on a body of water - providing us with free FEET OF HEAD: we will use an easy-to-remember and conservative estimation of 30 FT. for atmospheric pressure.
• Friction Loss in Intake Hose is estimated using a C-140 Head Loss Chart.  See Below. We have modified it for 25 FT lengths. example: 10" Hose at 2000 GPM = 0.5 FT
  
  
• NPSHr is found on the pump's curve at a given flow rate. example: 2000 GPM = 8 FT.

30 FT. – 0.5 FT – 8 FT. = 21.5 FT

21.5 FT = the maximum distance from the top of the body of water to the center of the pump impeller that this pump can operate at without being force-fed and without cavitation at 2,000 GPM.  If you drop the flow rate, these numbers change and it has less NPSHr, and more Static Suction Lift

Call or write with Questions!

712-653-3045 - PCE Office

nancypuck@gmail.com - Nancy
bpuck@puckenterprises.com - Ben
jpuck@puckenterprises.com - Jeremy