max. discharge

[wookiyo]

Max dis pressure can be increase by the additional differntial pressre due to following conditions ;
a. max. realtive density
b. max. dia. impellers or no. of stages
c. operation to trip speed

How can I assess and compare the possibility of the above ?
and what's mean "trip speed" ?

 

[checman]

Wookiyo Trip speed (rpm) is normally applied to steam turbines and if exceeded the turbine steam supply is shut off to keep the turbine from running at higher than recommended speeds. All of the terms are applied to centrifugal pumps. You can evaluate those by looking at the pump curve. Also you can get an increase in discharge pressure by increasing inlet pressure.

Regards checman

 

[25362]

The "model laws" for geometrically similar centrifugal pumps, call for the following proportionality:

H [ε] (n.D)²​

Where H is differential head; n, rotating speed; D, diameter of the impeller.

Strictly speaking, the model laws are only applicable at constant efficiency.

In a great number of cases the highest permissible speed of a pump "n", is determined by its suction performance or the required available NPSH. For a given flow, head and NPSHa values, the permissible speed can be increased by the following measures:

-using impellers of various shapes
-using double-entry first stage impeller
-installing an inducer
-using a booster pump

As for other factors affecting developed heads on centrifugal pumps:

Although most pumps can handle a small quantity of gases w/o losing their priming, dissolved gases, for example free air, will reduce differential heads as the vol% increases.

Additional frictional resistance as imposed by flowing fluids with higher viscosities may also reduce the developed differential head. More NPSH should be made available for higher viscosities.

Addition of inducers may help to increase head at lower flow rates, especially when recirculation at the impeller inlet is present.

Removing part of the shrouds on the impellers may increase heads at low flowrates and at shutoff.

Sharpening the ends of impeller blades may increase heads at all operating flow rates.