Is the pump directly connected to the motor so that each revolution of the motor causes a fixed ratio of revolutions in the pump?  For example, a transmission, clutch, belt(s), or other connection(s) might be important. Moreover, some motors are more efficient in certain ranges; so it would help to know the type of motor and fuel or power source.

Finally, do you have a way to measure the flow at different RPM's?  It would seem important to distinguish efficiency of the pump from efficiency of the motor.  I am not sure if this helps; however, it is an interesting question and I bet my answer will encourage others. 

tanks for answer

The purpose is to calculate the efficiency of motors. We know the electro-pump efficiency  but not the motor or pump efficiency separately.

Operational Condition is:

- Pump directly connected to the motor without any connection

- there is not any VSD and motor work in a fixed speed

- Motor Type: 3-ph Asynchronous induction motor

- Motor Nameplate Power: 200Kw

- Motor measured speed (rpm): 1400 (measured rpm)

- Motor Nameplate speed (rpm): 1496

There is no direct relationship between motor efficiency and its rotational speed. However all piston engines have a mechanical efficiency which is a maximum at a specific speed of rotation. Consequently a means for estimation of the best efficiency is the distribution of this tachometer speed reading with time. The most efficient use of the engine is when this speed more often is close to or equal to the ideal value noted above. Overall efficiency of piston engines is about 40% at best and older designs of motors are considerably less.

In the case of an electrical motor (the questioner does not specify which kind), the greatest efficiency is similar, but is usually designed into the motor characteristics to be at or close to its maximum permissible rotational speed. Here the efficiency can be as high as 95%.