thank u for ur answer but this link is speake about changing rpms it is available to change the pump head by change pump capacity with constant RPM and how ?russ_watters said:Have a look at the pump affinity laws: http://www.engineeringtoolbox.com/affinity-laws-d_408.html
Pump head is the measure of the energy required to move a fluid through a pump system. It is directly related to flow rate, as the higher the pump head, the higher the flow rate will be.
The pump head and flow rate relationship is affected by factors such as the type of pump, the speed of the pump, the fluid viscosity, and the size and length of the pipes.
The pump head can be calculated using the Bernoulli's equation, which takes into account the fluid's density, velocity, and elevation. The flow rate can be calculated using the equation Q = VA, where Q is the flow rate, V is the velocity of the fluid, and A is the cross-sectional area of the pipe.
The optimal pump head and flow rate for a given system will depend on the specific needs and requirements of the system. Factors such as the desired flow rate, the pressure requirements, and the type of fluid being pumped should be considered when determining the optimal values.
If the pump head and flow rate are not properly matched, it can result in inefficiency and damage to the pump system. If the pump head is too high, it can lead to excessive energy consumption and wear on the pump. If the flow rate is too high, it can cause cavitation, which can damage the pump and reduce its efficiency.