Hydrophore filling pumps running of curve 1

[samski]

Good morning,

As a student Marine Engineer and Electro Technical Officer I have to complete a thesis. This is a report focused on answering a research question. The engineering team onboard has suggested that I research the feasibility of installing frequency drives on the hydrophore skid.

The current hydrophore is a setup with two 1500L buffer tanks under 7.5 bar pressure, with three multistage self-priming pumps, capable of a total of 30m3/h. These pumps are used (not at the same time, alternating to keep the running hours equal) to fill the pressure vessel.

I have taken the pump curve from the datasheet of the pump and plotted this in Excel, together with the calculated (according the affinity laws) pump curves with lower speed. I have also calculated the system curve. The static head is high, as the pumps turn on at 6.5 bar and stops at 7.5 bar. The friction head is quite low because it is a small pumping system (around 20m of pipe with various fittings etc, pump suction height equal to the tank suction height and the discharge is also on the same level), resulting in a flat system curve.

But now I measured and calculated the average flow of the pump around 11 m3/h during a filling cycle, which is way of the crossing point of the system curve and 100% operating curve.
I hope you could explain me why this is.


Kind regards,
Sam

 

[samski]

Morning,

Found out yesterday night that I have been messing up between the 50 Hz en 60 Hz curves myself. Sorry for the confusion.

According the manual and drawings, the pumps has two stages. As for the impeller diameter, I have attached the documentation of the pump that is used on board for maintenance etc. (

https://files.engineering.com/getfi...lMultistageSelfprimingPumps_Azcue_121029.pdf)

There is a lot of sizing, but none of the impeller. I have tried contacting the original manufacturer, but they don't respond.

This is the 60 Hz curve with the points I measured.

What I do see is that the 9.5kW point and my calculated system curve are relatively close. But I don't understand how it is possible for the flow and power points to be such far apart from each other.


Kind regards,
Sam

 

[LittleInch]

The thing missing is the specific data sheet for the pump.

The nameplate you supplied on 19th May indicates that the pump has a duty point of 10m3/hr @80m diff head.
this tells me that the impellors have been modified in some way. The main data sheet says 20 stages which is very high - maybe they only mean 2 stages.

You need to find the actual data sheet supplied by the vendor which should provide more information.

It would also be interesting to see what power the motor is. If its 10kW or less than it can't be the same as the default max 51/20

The attached document gives 4 different motor sizes for 51/20, 4,5.5, 7.5 or 11kW. Again this tells me that they trim the impellor to match the customers requirements and then put in the smallest motor thay can.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.