npsh requis et npsh disponiblenpsh requis et npsh disponible

See also:

Create a new pump or fan Compare network load curves and pump operating point

Npsh net positive suction head:

the required NPSH and NPSH available

 Imagine a vertical tube one meter in height filled with water, to raise the water column should be a depression to the top of the column, at least equal to the pressure (generated by the weight of water) at the bottom…  the higher the colomn of water is, the higher the depression should be..

If the negative pressure necessary for raising the water column, drops the liquid pressure below the threshold of "saturation vapor pressure" the liquid turns into gas in the region where pressure is the lowest (usually at the point of maximum acceleration of the fluid), the fluid cavitate.

The water level at the suction limits the depression it is possible to create without cavitating

If the water level is too important to be raised without cavitation, it will be necessary to place intermediate pumps ...

This possible depression before cavitation is called NPSH (net positive suction head) available.

network interface pumps / turbines

In mecaflux NPSH available is calculated automatically when you enter the suction head. 

So far we have only raised the water column without giving it a speed, to moves liquid at a certain rate, the pump must generate additional depression. This pressure must be even greater than the desired flow rate is important.

This additional pressure related to the flow of the pump is called the required NPSH.The pump manufacturer provided a graph where we see the curve binding NPSH required to the flow. Usualy the required NPSH values, ​​vary from 0.5 to 3 mcf

If a column of water is so heavy, that it allows the possibility of only a very low sucking (available NPSH) before cavitation, we can only apply a small additional suction (required NPSH) therefore a low flow ...

 

If the water level is too important to be raised without cavitation, it will be necessary to place intermediate pumps ...

Example curve binding required NPSH, in meters of fluid column (mcf) to flow rate:

curve binding required NPSH, in meters of fluid column (mcf) to flow rate

 

charge hydrostatique derive aerodynamique hydrodynamique construire aile foil construire eolienne dimensionner conduits fumée carene dirigeable construire helice propulsion derive aerodynamique hydrodynamique frottement sur une surface de coque trainée resistance au vent trainée resistance au vent construire eolienne trainée resistance au vent conception helice bateaux derive aerodynamique hydrodynamique carene dirigeable frottement sur une surface de coque construire aile foil construire aile foil conception hydrolienne calcul voile frottement sur une surface de coque trainée resistance au vent calcul voile construire aile foil construire eolienne construire helice propulsion aeraulique aspiration air systemes ventilation aeration pertes charges vannes debit et pression conduits pompes et ventilateurs vidange reservoir construire aile foil Logiciels de la suite Mecaflux Forces sur des objets géometriques dans un courant de fluide ramification et boucles réseaux dimensionner conduits fumée calcul systemes réseaux fluides gaz liquides helice a vitesse nulle sustentation resistance aerodynamique vehicules calcul debit rivierre helice de captage turbine Kaplan hydroelectrique charge hydrostatique carene dirigeable construire helice propulsion derive aerodynamique hydrodynamique