7 replies to this topic

[Pingue2008]

Dear all,

 

1-I have been assigned to check the head (actual head) verse the head from the vendor datasheet. I calculated the head and they seem to be ok for me (Head from vendor datasheet > calculated value). To be précised the flow from the vendor data sheet is not the same as the one I picked from the PFD. vendor datasheet (Flow=2032gpm, Head=154ft) calculated/PFD value (Flow=1616 gpm, Head=147ft). Now I am trying to check my data against the system curve. My operating point (Flow=1616gpm, Head=147ft) does not fall on the curve. Question: how can arrive at a conclusion given this situation.

 

2- what is velocity criteria when a flow is driven by gravity? I have all kinds of number (3- 14 ft/sec).

 

Thank you,

[mansari]

Actual Lower head and lower flow as compared to the design indicates that the pump is not operating on its curve. However you have to validate it through detailed calculations based on the installed system.

 

Pump head means the differential head, added by the machine. This is calculated by subtracting suction head from discharge head. What is the method you have used for flow measurement? How accurate it is? Is this date in agreement with pump power input? Are you using a fluid different than water? Most of the pump curves are based on water.

[markymaark]

To be clear-- are you saying the pump provided by the vendor has a greater head and design flowrate vs. what you specified.  And now you are wondering if the vendor's pump is the correct pump for your application since your operating point does not fall on the curve?

[Raj Mehta]

Can you share your calculations and the characteristic curve shared by the vendor ? Also answer the questions asked by Mr. Mansari.

 

Thanks

[Pingue2008]

Dear all,

 

sorry for the late response.

1- The flow is a 16%wt brine solution. I used the 3D plant model(Navisworks) to determine the height and length fittings etc...

2- I am working behind the previous engineer. the assignment was to see if the pump can still handle the flow. we were currently trying to increase

 the plant capacity by a factor of 1.26.

3- the calculations I carry out were very simple head (distance from pumps center line to final discharge point) + losses due to fitting and length were estimated by Engineers' Aid (Sinet). plus 40psi for the filter.

4- see attachment.

 

Thank you,

 

Attached Files

•  Cap.JPG   203.91KB   5 downloads

[vinay1999]

Dear all,

 

sorry for the late response.

1- The flow is a 16%wt brine solution. I used the 3D plant model(Navisworks) to determine the height and length fittings etc...

2- I am working behind the previous engineer. the assignment was to see if the pump can still handle the flow. we were currently trying to increase

 the plant capacity by a factor of 1.26.

3- the calculations I carry out were very simple head (distance from pumps center line to final discharge point) + losses due to fitting and length were estimated by Engineers' Aid (Sinet). plus 40psi for the filter.

4- see attachment.

 

Thank you,

 

 

Check for the head if its was given as MLC /MWC in the data sheet.The curve should be for the liquid handled.If it was given for water (mwc) then your power consumption will increase if used for brine solution.If there is no KW cushion in your motor you will have lesser head generated 

 

Going by your earlier post , you may have to trim the impeller suitably to get your duty conditions as you have cushion in your pump.Or you should use a VFD control drive and get head flow curve at various speeds (rpm)  from the manufacturer.

Edited by vinay1999, 13 June 2013 - 08:41 AM.

[vinay1999]

Our system has two vertical turbine pumps running in parallel with two standby units.The fluid is sea water (sp gr. 1.030) and the duty point of the pump is 47.04 mlc bowl head  @5475 m³/hr flow. We observed that we could not get the requisite flow from two pumps and took the third pump online. Now however the pressure gauge at each  pump outlet reads 5.2 bar  and we have a suction lift of 1.65 m making the total bowl head as 53.65 mlc .As per the pump performance curve it should give a flow of around 4200 making the total flow from three pumps as 12600 m3/hr.But ironically we get only 9600 m3/hr ( we have a mag flow meter downstream ) with three pumps.

 

Going by the pressure gauge reading i think the flow is not correct. Now I doubt the suction of the pump. I would like to take the opinion from people if the suction has got turbulence/vortex  will it effect the suction lift to such an extent? The pumps are placed @ 4m centre to centre distance.

 

The pump is from a reputed manufacturer and is an API pump.So before doubting the pump performance i would like to check with the experts here.

 

https://docs.google....Ydmc/edit?pli=1

Edited by vinay1999, 14 June 2013 - 04:48 AM.

[breizh]

Consider this resource to support your query , in particular the chapter 4 .

 

Breizh