Vertical Multi-Stage Centrifugal Pumps

Calculation Of minimum Inlet Pressure

If the pressure in pump is lower than the vapour pressure of medium, cavitation will occur, which will affect the performance of pump. To avoid the cavitation and ensure the pump inlet has a minimum pressure, maximum suction head should be calculated as following:

H=Pbx10.2-NPSH-Hf-hv-Hs

Pb: Atmospheric pressure, bar (In close pipeline system, it can be considered as the system pressure );
NPSH: Net positive suction head, m (Value at maximum flow of Q-NPSH curve);
Hf: Suction pipe line loss (Value at maximum flow of corresponding pipeline);
Hv: Medium vapour pressure, m (Medium vapour pressure at corresponding temperature, the default medium is water, as shown in figure4 on the right );
Hs: Safety margin, m, general value is 0.5.
Calculation result: if H is positive, the pump is installed in suction way, otherwise, it is installed in downdraft way.

Note: It is not necessary to do above calculation under general conditions. Only when we use pump in the following situations do we need to calculate the H:
1. Medium temperature is high;
2.The velocity of flow is larger than rated value;
3.Suction head is big or inlet pipeline is long;
4.System pressure is small;
5.Inlet condition is bad.

Selection Of Pumps

Selection of pumps should be based on:
Duty point of the pump.
Dimensional data such as pressure loss as aresult of height differences,friction loss in the pipework,
Pump efficiency etc.
Pump materials
Pump connections
Commonly used mechanical seal configuration tables

1. Duty point of the pump:

From a duty point it is possible to select a pump on the basis of the curve charts shown in "performance curves/technical" data.

2. Dimensional data:

When sizing a pump the following must be taken into accounting: •Required flow and pressure at the draw-off point. •Pressure loss as a result of height differences. •Friction loss in the pipework(Hf) (Refer to Fig.1) It may. •Best efficiency at the estimated duty point. •NPSH value. •For calculation of the NPSH value, see corresponding curves chart.

3. Pump efficiency:

Before determining the best efficiency point, the operation pattern of the pump needs to be identified. If the pump expected to operate as the same duty point, then select a BL pump which is operating at a duty point corresponding with the best efficiency of the pump.
As the pump is sized on the basis of the highest possible flow, it is important always to have the duty point to the right on the efficiency curve(eta) in order to keep efficiency high when the flow drops.

4. Pump material:

Selection of pump connection depend on the rated pressure and pipe work. the pump offer a wide range of ftexible connection such as:

5. Commonly used mechanical seal configuration tables

Application Field

Shaft seal type

Shaft seal material

Normal

Special

1

2

3

4 5

Type key

Rotating part

Code

Stationary part

Code

Elastomers

Code

Compression spring

Collor

Code

0℃ to +90℃ clean water

●

Graphite

A

SiC

S

FPM

F

SUS304

C

ASFC

0℃ to +90℃ clean water

●

WC

W

Graphite

A

FPM

F

SUS304

C

WAFC

+90℃ to +120℃ corrosion resistance

●

SiC

S

SiC

S

EPDM

E

SUS304

C

SSEC

up to 0℃

●

WC

W

WC

W

EPDM

E

SUS304

C

WWEC

Mechanical seal type	Pump model	d1	d2	h
NJK	BL(T)2/4	12	12	55
	BL(T)8/12/16/20	16	16	57.5
	BL(T)32/45/60/90	22	22	72
NDA	BW(J)2/4	12.7	16	32
	BW(J)8/16	17.4	20	33.5