4 replies to this topic

[Meysam_45000]

Dear Friends,

I need to know whether I calculate the required brake horsepower for a duplex plunger pump in a correct way or not.

We want to purchase a plunger pump with following operating conditions:

Handled liquid: steam condensate

Operating temperature: 38°C

Discharge pressure: 63 bar

Suction pressure: 0 bar

Normal Capacity at operating temperature: 3.44 m³/hr

Specific Gravity: 0.993

Viscosity (cP): 0.68

Moreover, it is possible that we work with the capacity about 3.9 m³/hr for a short period of time.

 

Based on API 675 (2.1.15) I calculate the rated capacity 10% greater than Maximum capacity which is 3.9*1.1= 4.29 m³/hr.

I calculate the BHP of PD pump based on 85% efficiency and rated capacity, the equation is Q×ΔP/η. The estimated required BHP is 4.29*63*100000/(3600*0.85)=8.83 kW.

Am I right!?

It would be grateful if you could help me.

[ankur2061]

Your answer is right. but why are you complicating the formula:

 

It is just:

 

BkW = Rated flow rate (m3/h)*ΔP (bar)  / (36*η as a fraction)

 

And please make it a practice to mention suction or discharge pressures in either absolute or gauge units.

 

Regards,

Ankur

[Meysam_45000]

thank you for your answer!!

I have seen somewhere that required BHP is (calculated BHP)*(1.2). I mean 20% greater than what I calculate.

I do not know whether I should multiply the calculated BHP (8.83) by 1.2 or not!?

what should I report as a required BHP!!? 

8.83 kW or 10.60 kW

 

another question is that currently we do not know about the specification of the supplier's pump. Are we able to purchase the electric motor by this information (required BHP)? 

Thank you for your help.

[ankur2061]

Why would anybody want to buy the motor separately? Pumps are procured with motors. It just doesn't make sense to buy a motor separately.

Just provide the specification of the pump to the manufacturer and he will supply the pump with the motor.

 

Regards,

Ankur.

[Meysam_45000]

thank you so much!!

by the way, I have some confusion about the formula that represents by API 674 about BHP.

single-acting power pump and double-acting power pump.

there are two different formula for these two pump.

single-acting power pump BHP: kW=(Q*DeltaP)+(Q*Pd)...

double-acting is as I previously said.

which one is suitable for me.

I now that plunger pump is a single-acting power pump but I do not know that about duplex or triplex plunger pump.

if all of them are single-acting pump then I should correct the required BHP.