There are 6 kinds of protection lines for the pump, which are used to protect the pump body from damage and normal operation, and set the protection pipeline of the pump according to the conditions of use.

(1) Warm pump line——When the temperature of the medium is higher than 200 °C, when there is a spare pump, the DN20～25 warm pump line should be set;

(2) Small flow line——When the working flow of the pump is lower than 30% of the rated flow of the pump, the small flow line of the pump running normally at the lowest flow rate should be set;


(3) Balance line—for conveying a liquid with a saturated vapor pressure higher than atmospheric pressure at normal temperature or a liquid in a bubble state, in order to prevent steam from entering the pump liquid or air bubbles entering the pump, the cavitation should be balanced;


(4) Bypass line - When the pump is used for trial operation or when the outlet main valve is closed under abnormal operating conditions, the pump can still be operated. Generally, a bypass valve with a limited flow hole is provided in a case where the pressure difference between the valve and the front is very high;

(5) Anti-coagulation line - When conveying liquid with high pour point or high freezing point solidified at normal temperature, the backup pump and pipeline should be equipped with anti-condensation line to avoid plugging of spare pump and pipeline;

(6) Safety valve line——For the volumetric pumps such as electric reciprocating pump, gear pump and screw cylinder, the safety valve line is set on the outlet side. When the outlet pressure exceeds the constant pressure value, the safety valve takes off and the fluid returns to the pump population tube.

Second, the minimum flow line of the centrifugal pump has the following effects:

(1) When the centrifugal pump is operated at a low flow rate, fluid detachment may occur in the pump, which may cause vibration and noise of the pump. Set the minimum flow line to ensure that a certain amount of fluid flows through the pump after the pump is started to prevent cavitation;

(2) When the centrifugal pump with high power is running when the outlet valve is closed, the fluid in the pump will become hotter and hotter. In severe cases, the bearing will be burnt out. After the minimum flow line is set, it can ensure that there is always a certain flow during the operation of the pump. The liquid flows through the pump to prevent this phenomenon;

(3) When working at a small flow rate, the pump shaft will be subjected to additional radial force. The minimum flow line can be set so that when the pump is running, a certain amount of fluid flows through the pump to prevent the pump shaft from being subjected to excessive radial Force effect

(4) Sometimes the orifice plate is used on the minimum flow line of the pump, so that even if the pump outlet valve is closed due to misoperation, the centrifugal pump can be safely operated without causing damage. The advantage of the restrictor orifice plate is that no manual adjustment is required. If only the shut-off valve is used for adjustment, it is difficult to control the flow rate near the minimum flow of the pump, either large or small.


Third, the difference between each flow line

(1) Distinguish between small flow lines, and circulation lines. In the normal production, the former has a flow rate less than 30% of the rated flow rate, and the latter is used in places where frequent switching or prevention of clogging is blocked. The same point: the flow rate of the pump is much larger than the flow required by the actual process.

(2) Distinguish between minimum continuous steady flow and minimum continuous heat flow. The minimum continuous steady flow rate refers to the minimum flow rate at which the pump can work normally without exceeding the noise and vibration limits specified by the standard. It should generally be measured and provided to the user by the pump factory. The minimum continuous thermal flow is the minimum flow that the pump can run continuously without being lost by the temperature rise of the pumped liquid.