6 replies to this topic

[radames.rios]

Greetings! I’m currently looking for a pump system that would provide me a 6.5 bar pressure head for a flow of 400 GPM (Cooling Water). Would it cause any problem if the pump inlet line is 4” in diameter and the outlet line diameter is 8”? What system would you recommend? I'm worried about cavitation. The tubes are carbon steel and lower rpm pumps are preferred.

[Fr3dd]

<sub>Hello,

I think that, in order to answer that question, additional data should be provided. A 4" line handling 400gpm of water may have slightly high velocities 12 ft/s (I think it's better to stay below 10ft/s). However, you should take into account the whole system: from where to where you are pumping?, is it a long distance?, is there a considerable height difference?.

All this data is necessary for an estimation. If you're worried about cavitation, you should check. You'll need then also the temperature of the fluid, etc. I'm sure a lot of people over here may want to help you, but you need to be more specific.

Regards,


Regards,</sub>

[S.AHMAD]

1. Industrial practices is normallly the suction pipe is bigger than the pump discharge piping. 1 pipe size bigger is common.
2. Howevrt, the correct way is to check the NPSH available and compare to the pump NPSH required (by pump vendor).
3. If NPSH avaialble is greater than the NPSH required, then the system is OK. Otherwise select the next bigger size and recheck NPSH.
4. As a rule of thumb start the inlet velocity about 1 ft/s. Determine the x-area and hence the pipe diameter. Check for NPSH.

[Dacs]

I think all has been said here, but for emphasis, a full hydraulic analysis is in order here, especially when considering NPSHa calculation where placement of equipment (how far and how high the source vessel is) is important.

From there, you can make your decision if you can use the pump in question.

[Rahimzadeh]

Dear radames:
Due to lower friction losses and more NPSH ,the pump inlet diameter selected bigger.

[Art Montemayor]

Radames:

S.Ahmad has given you detailed and correct advice. You seem to have your relative pump piping sizes backwards. The suction side size is normally always larger than the discharge size. The 1 ft/sec velocity is a normal, conservative velocity to start with to check out your NPSHa. You should normally have a NPSHa that is 1.35 times the NPSHr (Required Net Positive Suction Head) - AS A MINIMUM.

[breizh]

Radames,

Consider this resource too, very much in line with what wrote S AHMAD and ART .
Hope this helps.

Breizh