Waramanga
Mechanical
- Jun 21, 2009
- 170
Hi Guys,
I am a HVAC engineer and am trying to understand NPSH better. I understand that you need a minimum amount of absolute pressure at the suction of a pump to prevent cavitation. Some pumps that I have looked at it is 1.5m of head, which is 15kpa or so. In normal HVAC closed systems we run them above atmospheric pressure, say around 400kPa or so. Say I was running a hot water system with 90 degree water in it, to avoid cavitation all I need to do is keep the suction above 385 absolute and there wont be cavitation? The reason I ask is because I am looking at a design which has a decoupled primary secondary pumping system. The secondary punmps sit out in plantrooms with varying distances to them and boiler plant, with between 15kpa and 60kpa suction line pressure drop to them. I think that this should be OK, some of the pumps will an absolute pressure at their intake lower than the system pressure but higher than the the min NPSH for the pump. All OK???? Does this system make sense. Usually we have all the field pumps in the boiler room with very short lines of equal length back to the primary circuit. What do you think?? attahced is a sketch...
Thanks for your help
I am a HVAC engineer and am trying to understand NPSH better. I understand that you need a minimum amount of absolute pressure at the suction of a pump to prevent cavitation. Some pumps that I have looked at it is 1.5m of head, which is 15kpa or so. In normal HVAC closed systems we run them above atmospheric pressure, say around 400kPa or so. Say I was running a hot water system with 90 degree water in it, to avoid cavitation all I need to do is keep the suction above 385 absolute and there wont be cavitation? The reason I ask is because I am looking at a design which has a decoupled primary secondary pumping system. The secondary punmps sit out in plantrooms with varying distances to them and boiler plant, with between 15kpa and 60kpa suction line pressure drop to them. I think that this should be OK, some of the pumps will an absolute pressure at their intake lower than the system pressure but higher than the the min NPSH for the pump. All OK???? Does this system make sense. Usually we have all the field pumps in the boiler room with very short lines of equal length back to the primary circuit. What do you think?? attahced is a sketch...
Thanks for your help
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