NPSH 2

[darafotouhi]

Hi
I am redesigning a cooling water system now. This system have a 65-250 centrefugal pump and pump & cooling tower in the same level.The work of system is not satisfactory. pump & cooling tower need any diffrence level because of NPSH?
I aplogize for poor English writting.

 

[vpl]

Does your pump get its water from the cooling tower? Also what's wrong with the system performance - is the pump cavitating, for example?

 

[pardal]

Hi I have a lot experience in cooling towers and pumps.

Normally the pump is just a few distance down from water level at the tower bassin.

There must be a " Y " filter between the tower and pump. chek if it is clean.

Please give me details:
Pump brand
Pump model
Pump flow:
Pump head pressure:

Intake diameter.
Tower capacity in BTU or KCAL
Model
Brand

apliccation:
HVAC ?


Pipe diameter from tower to pump
Level from water level at basin to pump intake





You can reach me at k281969@hotmail.com
but keep your post here for mutual benefits.
Pardal

 

[darafotouhi]

dear freinds
the pump get water from cooling water and have problem and abuse something like cavitation.
pump brand:toss
pump model:65-250
pump flow:375 gpm
pump head:80 m
intake diamiter:6"
tower capacity:120 ton
application: industrial cooling
thank you

 

[TD2K]

Darafotouhi,

Have you calculated the NPSHA for the pump? It's not automatic that the pump MUST be lower than the water level in the cooling tower basin though first that's a good practice and is also pretty common.

The velocity in the inlet line is about 4.2 feet/sec which should be fine. You need to check the pressure drop from the cooling tower basin to the inlet of the pump and include the head difference (positive or negative) between the water level in the basin and the centerline of the pump suction. The NPSHA value must be greater than the NPSHR which will be shown on the data sheet for the pump.

If there are any suction valves, you need to ensure they are fully open (you might want to consider X-raying them depending on the type) and any suction strainers aren't clogged and taking a pressure drop.

 

[quark]

Darafotouhi!

If your pump and cooling tower are in same level and if you ensure water level in cooling tower is atleast above suction of pump (ideally should be discharge flange of the pump) there won't be any cavitation. NPSH of a water pump will come into picture for only negative suction pump. If you can be more elaborative about your problem some solution can be thought of.

PS: Check strainer and discharge pressure of pump

Regards,

 

[butelja]

In addition to checking the NPSH, you should also verify that there is adequate submergence to prevent vortexing air into the pump. The formula from the Hydraulic Institute standard ANSI / HI 9.8-1998, Section 9.8.7 is:

S = D + [(0.574*Q) / D^1.5]

S = minimum required submergence, (inches)
D = suction bell diameter, (inches)
Q = U.S. gallons per minute (gpm)