2 replies to this topic

[Bodhisatya]

Dear All

 

Requesting esteemed members to help in understanding how specific speed of a rotary equipment is defined and what is its physical significance.

 

Bodhisatya

 

 

[Lucian Gomoescu]

Hello,

Specific speed of a rotary equipment represents the impeller speed which would develop a head of 1 unit at a flow rate of 1 unit.
Thus:

Ns = N * (Q/Qs)^0.5 / (H/Hs)^0.75
 

, where:
Ns - specific speed of impeller, rpm
N - speed of impeller, in rpm, at which flow rate is Q and head H;

Qs = 1 unit of flow rate (gpm or m3/hr);

Hs = 1 unit of heat (ft or m);

Of course, Qs and Q, respectively H and Hs units must be the same within the calculation.

Specific speed helps the designer of the equipment in selection of impeller type.
For example, what impeller type to use in order to have the required efficiency, if the application requires a flow rate Q and a pump head H, at a shaft speed N ? Based on the calculated Ns, the designer looks on a diagram an makes a decision.

It is also helpful in determining the impact on pump efficiency in case of changing operating conditions for a pump already in operation.

For further documentation I suggest "H P Bloch - Pump Wisdom Problem Solving for Operators and Specialists" (chapter 1).
 

[breizh]

Hi,

consider this resource for a centrifugal pump:

 

http://centrifugal-p...definition.html

 

 

Breizh