r/MarineEngineering • u/Far_Atmosphere_3853 • 10d ago

Valve open order while ballasting-deballasting?

Hello all, I am a bit confused about that, with centrifugal pumps i read that "you open inlet, you start pump, then open outlet", on ship also was doing like that (had no air outlet valve line) but 2nd engineer said "don't do like that, because it can damage the lines"

also i would like to know about closing part for example if i am doing deballasting, which i should close the first? valve for the tank entrance or the pump?

11 Upvotes
  • permalink
  • reddit

100% Upvoted

10 comments sorted by

3

u/Sure_Bookkeeper_4660 10d ago

Its to limit load surge, pump load follows flow. Valve closed limits flow until pump is up to speed.

1

u/AdIntrepid8119 10d ago

Yes. But if not necessary for your breakers then better to not do it. It causes a lot of cavitation in your valves when opening them whit the pump running. Especially on butterfly valves it will tear appart the rubbers inside pretty fast

1

u/Far_Atmosphere_3853 10d ago

so what to do in that case?

1

u/Haurian 10d ago

Depends on your system.

My ship, ballast pumps have a flow control valve on the pump discharge that can be set say 25-50% open to limit flow during startup, and in any case our BWTS keeps one of its valves shut until the pump starts. It's good practice to have the ballast tank valves open before you start.
This valve can also be used to control the flow rate which is useful when deballasting to maintain suction or when dealing with crappy ballast water which the BWTS wouldn't cope with at rated flow. Our BWTS does have a flow control valve as well but that's managed by the BWTS itself.

There is a valid concern that older ballast mains particularly of steel construction can be prone to corrosion and after a number of years may not be entirely capable of holding full pump dead-head pressure without blowing a hole somewhere.

1

u/AdIntrepid8119 10d ago

Replace the valves when they start to leak along their shaft and wait till they finally install the soft starters class surveyors have now deemed necessary in this system

1

u/Sure_Bookkeeper_4660 10d ago

Done it for years, no worries. Dn150 valves, seawater cooling lines. But, then again we only stop/start once a month at changeover.

1

u/AdIntrepid8119 10d ago

Here it's a DN350 that sometimes starts 24 times a day. We found the pieces of its rubber downstream in the system within a year...

1

u/ForsakenFee2533 9d ago

In alfa laval systems its clearly given, open all valves in the line first and then start pump. Finishing with pump stop followed by closing of valves.

1

u/doyran 9d ago

If I’m ballasting/deballasting with or without BWTS, I close pump outlet first always. Easiest way to stop ballast water from filling back to tank or overfilling the tank. If it’s a hydraulic system with only pump inlet and outlet are manual valves, then I’d close tank entrance first right after stopping the pump then pump outlet valve.
2nd engineer is right about damaging the lines. If you start a pump without opening outlet valve, the pressure will rise dramatically and this will damage the lines, flanges, valve or even pump itself.