The multistage centrifugal pump is a combination of two or more centrifugal pumps having the same function. On the fluid passage structure, the medium pressure discharge port shown in the first stage communicates with the inlet of the second stage, and the second stage of the medium discharge The pressure port communicates with the inlet of the third stage, and the mechanism connected in series forms a multistage centrifugal pump.
Reasons for pressure drop in multistage centrifugal pumps:
1. Motor reversal
Due to the wiring, the steering of the motor will be reversed from the actual demand of the centrifugal pump. In general, the steering of the pump should be observed first. If the steering is reversed, any two wires on the terminal on the motor should be exchanged.
 2. The operating point is shifted to the high flow and low head
In general, multistage centrifugal pumps have a continuous downward performance curve, and the flow rate gradually increases as the head reduces. During the operation process, for some reason, the back pressure of the pump reduces, and the working point of the pump passively shifts to the low-head and large flow point of the device curve, which causes the head to decrease. In fact, this is due to external factors such as the device. The change caused by the pump has no special relationship with the pump itself. At this time, as long as the pump back pressure increases, such as closing a little outlet valve, the problem can be solved.
 3. The low speed
The important factors affecting the head of the multistage centrifugal pump are the outer diameter of the impeller and the rotational speed of the pump. Under other conditions, the pump head is proportional to the square of the velocity. The effect of the velocity on the head is very large. Sometimes, because of the external temperature, the pump speed reduces, which will reduce the pump head. In this case, check the speed of the pump. If the speed is not enough, check the cause and solve it reasonably.
 4. Cavitation at the inlet
If the suction pressure of the multistage centrifugal pump is too low, below the saturated vapor pressure of the pumped medium, cavitation will form. At this time, check whether the inlet piping system is blocked or the inlet valve opening is too small, or increase the liquid level of the suction pool.

5. Internal leakage
When the gap between the rotating part and the stationary part in the pump exceeds the design range, it will cause internal leakage, which is reflected by the discharge pressure of the pump, such as the impeller ring gap and the interstage gap of the multistage pump. At this time, the corresponding disassembly inspection should be carried out to repair or replace the parts that cause excessive clearance. 
6. Impeller flow channel blockage
If the flow path of the impeller is blocked, it will affect the work of the impeller, resulting in a drop in the outlet pressure. Therefore, it is necessary to remove the pump to check for foreign matter. To prevent this from happening again, a filter can be added before the pump inlet if necessary.
Multistage centrifugal pump has the advantages of high efficiency, energy saving, wide performance range, safe and stable operation, low noise, long life, convenient installation and maintenance, etc. It can transport hot water, oil and corrosion by changing the material of the pump, sealing form and adding cooling system. And abrasive media, etc.