Centrifugal pump installation should note the following basic questions:

( 1 ) Install the base surface must be smooth , clean and able to withstand the corresponding load .

( 2 ) a fixed place in the need to use anchor bolts.

( 3 ) for vertical mounting of the pump , anchor bolts must have sufficient strength .

( 4 ) If the vertical mounting , the motor must be located above the pump .

( 5 ) When fixed to the wall , pay attention to alignment, alignment.

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      Pump power and efficiency

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During operation of the pump because of various losses , the actual pump ( active) pressure head and flow rate lower than the theoretical value , and the input power of the pump higher than the theoretical value , set

H______ effective pump pressure head , the unit amount of the liquid in the gravitational field energy derived from the pump , m;

Q ______ actual pump flow rate , m3 / s;

ρ ______ liquid density , kg / m3;

Ne______ effective pump power of the liquid per unit time obtained from the pump mechanical energy , W.

Effective power can be written as Ne = QHρg

The pump motor input power is called the pump shaft power , N represents . Effective power and shaft power ratio is defined as the total pump efficiency η, i.e.

η = Ne / N

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First, the pump loss

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There are various types of losses within the pump :

( A ) volume loss

Since the pump is called the damage caused by leakage volume loss . No volume loss when the pump power and a volume loss when the pump power ratio is called the pump volumetric efficiency ηv.

( 2 ) hydraulic losses

Fluid flow through the impeller , the pump casing , the flow velocity and direction changes and reverse pressure gradient caused by the presence of the circulation and the vortex , resulting in energy loss , this loss is called hydraulic losses . Rated flow centrifugal pump hydraulic efficiency ηh is generally from 0.8 to 0.9 .

( 3 ) mechanical losses

High-speed rotation of the impeller and the friction between the liquid and the bearing , seal , etc. The mechanical friction losses caused called mechanical loss . Mechanical efficiency ηM is generally from 0.96 to 0.99 .

Operating point of the centrifugal pump with a flow regulator , the operating point

Centrifugal pump characteristic curve inherent characteristics of the pump , which has nothing to do with the external use . However, once the pump is arranged in a pipeline system, when working on their actual work is not only on the characteristics of the pump itself , but also on the operating characteristics of the pipeline . Therefore, to choose the right and the good use of centrifugal pumps , it would also have to take into account the characteristics of the pipeline .

In particular for transporting liquid pipeline , the pipeline pressure head He desired flow rate Qe as the square of the change . This relationship is plotted on the graph paper corresponding pipeline characteristic curve .

If the pump characteristic curve where the pipeline characteristic curve with its painted in the same graph paper , as shown above , the intersection of two lines M is called the pump operating point . When selecting a pump , the operating point corresponding to the required flow rate and pressure head piping system meets the requirements , but also happens to be centrifugal pump provided that Q = Qe, H = He.

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Second, the flow control

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     ( A ) change the valve opening

Change the valve on the pump outlet line switch , and its essence is to change the pipeline characteristic curve . As shown below, when the valve is closed hours, local resistance to increase pipeline , pipeline characteristic curve steepens , the operating point moves by the M M1, flow from the QM reduced to QM1. When the valve opening is large, the pipeline resistance decreases, pipeline characteristic curve becomes flatter , the operating point moves M2, traffic increased to QM2.

With the valve regulating the flow quickly and easily , and the flow can be continuously varied, suitable for continuous production of chemical characteristics . It is widely used. Disadvantage is that valve off hours, increase the resistance loss , increased energy consumption , not very economical.

(2) changing the pump speed

Changing the speed of the pump is essentially change the pump characteristic curve . The original speed of the pump is n, the operating point is M, as shown , if the pump speed is increased to n1, the pump characteristic curve H - Q moves up , the operating point moves from the M M1, to increase flow from the QM to QM1. If the pump speed is reduced to n2, the operating point moves M2, traffic dropped QM2.

This adjustment method requires expensive transmission speed or the prime mover , and it is difficult to achieve continuous adjustment of flow rate , so rarely adopted in chemical production

Head and flow

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   Current = head * Flow

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First, lift the level is determined by pipes and valves for water, energy loss and the decision, he said, can give the water pump energy value , of course, the motor speed also drops down when the pump head outlet valve off small , due to the head does not change, flow reduction, then the pump current is reduced , if it is fully closed the current minimum, but slightly larger than idling , because the water there is resistance .

Centrifugal minimum current when it is idling , it is not what the water pump body , and the atmosphere directly connected to the pump bye transfer [ of course submersible pumps such a long time can cause overheating switch is damaged , and even an ordinary pump , such transfer is not good.

The maximum pump current when it is connected to the source material when imported , such as water , while exports are not restricted, such as directly connected to the atmosphere , even the pipes are not connected , this time, the maximum flow rate , the pump current will be maximum .