4 replies to this topic

[chemmu]

Dear All,

I have a doubt in capacity of the pump


1. As per API 675, the rated capacity means the capacity at operating conditions.
So it clearly mentions that rated capacity and operating capacity are same.


2.As per data sheet mentioned in the standard, three capacity has been mentioned as minimum , maximum and rated.
What is minimum and maximum here ?


3.The same API says that " Rated capacity shall be at least 110% of the maximum capacity specified.

As per the statement, it is evident that rated capacity is more than maximum capacity.
How is it possible ? As per the point 1, the operating and rated capacity are same .

Please help me to understand ..

Regards,
Chem.M

[fallah]

Chem.M,

 

The min/normal/rated flow are to be specified by purchaser as per his flow requirements. The min flow would be normal flow time the min safety factor and the rated flow is equal to normal flow times the max safety factor. Obviously as per API 675, if the maximum flow would be specified by purchaser then the rated flow shall be 110% of the max flow even if the max safety factor would be higher than specified value...

[chemmu]

Dear fallah,

 

Thank u very much for sharing your view.

 

As per the standard if the rated flow is operating flow, then how will it be the rated flow is more than maximum flow ??

 

Shall we assume the maximum capacity is the design capacity or the rated capacity is the design capacity ?

 

Regards,

Chem.M

[fallah]

chemmu,

 

Positive displacement pumps, opposed to centrifugal pumps, have almost vertical flow vs head, let say, line and you cannot change the flow of them without a change in speed...Then if it is supposed the speed is constant, contrary to centrifugal pumps you would have almost fixed flowrate regardless of head developed or reduced. While you can create a flow higher than rated one in centrifugal pumps by head reduction, in PD pumps the flow would be nearly constant regardless of you named it operating, rated, design,...but because we have to specify our process requirement to min/max flow we would expect to receive from the PD pump, the standard would intend to remind us to get 10% overdesign on max flow to achieve the rated flow by which not only we create a room to cope with the inherent resistivity of the PD pump to deliver more flow with head reduction but also we would have adequate margin for future requirement to more flow...

 

Indeed, the rated flow would be the design capacity in PD pumps...

[chemmu]

Dear fallah,

 

Thank you so much for your valuable information

 

Regards,

M.Murugan