Pump vacuum rating

20

Ju 2014

Pump vacuum rating

Pump vacuum rating depends on its design and also on the pumped fluid relative density and temperature. By theory, water at temperature close to 0C can be lifted by the pump from an open reservoir to the 10 m height, when perfect vacuum is created in a suction pipe. In practice, maximum pump vacuum rating with cold water is up to 8 m, considering hydraulic friction and air leaks.

Pumps technical documentation (catalogues, certificates) contents acceptable pump suction head (or acceptable positive suction head, NPSH) for normal conditions, i. e. for atmosphere pressure 0.1 MPa (that corresponds approximately to 760 mm Hg) and pumped fluid temperature 20°С.

 

Usually, the pump vacuum rating, which does not exceed 6 m, depends on the pump impeller design and also on the seal level elevation of the pump. 

!!! Pump suction head depends on the atmospheric pressure, pumped fluid flow rate and density, it’s temperature (and it’s vapors pressure, accordingly), and hydraulic friction of the suction pipeline.

Pump suction head dependency on the water temperature.

 Temperature ºС

10

20

30

40

50

60

65

 Suction head, m

6

5

4

3

2

1

0

 

Values of provided atmospheric pressure pа/pg (pа/pg — provided atmospheric pressure height, mH2O) depending on the site sea level elevation.

 Sea level elevation, m

-600

0

100

200

300

400

500

600

700

800

100

1500

2000

 pа/pg, mH2O.

11.3

10.3

10.2

10.1

10

9.8

9.7

9.6

9.5

9.4

9.2

8.6

8.4

 Pump vacuum rating decreases dramatically with the increase of the pump impeller specific speed. Therefore, the fluid is to be delivered with pressure to the pumps with high specific speed impeller.  

!!! Specific speed coefficient is a speed of a geometrically similar pump of such size that at the pressure of 1m it provides the discharge of 75 L/s. It serves for comparison of different types of pump impellers, pump selection at set efficiency, pressure  and number of rotation per minute, values of which are used from the optimal mode, according to the maximum pump coefficient of efficiency.