In the applications of Slurry Pumps, frequency conversion operation is sometimes required. For example, direct coupling connection must be achieved at some sites, or flowrate is unstable at other sites, or the transport distance is relatively long etc.. Hence, frequency converters are needed to adjust the speed of the slurry pump so that the pump discharge pressure matches the actual required one.
In the process of frequency conversion, people often consult about the lowest frequency: someone says it’s 25Hz, some says 30Hz, and some says 5Hz. Are these parameters correct? What is the exact value? The inaccurate setting of the minimum frequency in the control system will affect the normal operation of the slurry pump.

In fact, the above three frequency values come from two aspects. One is the driving equipment of the pump, i.e. the motor and another is the slurry pump itself.
I: the minimum operating frequency of VSD motors
1. Speaking of theory alone, the lowest operating frequency that a VSD motor can run is 0Hz, but a 0HZ motor has no speed, so this cannot be regarded as the lowest operating frequency;
2. The allowable operating speed range of different VSD motors is different;
3. To put it simply, if the speed regulation range of the VSD motor is 5-50Hz, then the minimum allowable operating frequency of the variable frequency motor is 5Hz;
4. The reason why the variable frequency motor can run at multiple frequencies.
(1) The VSD motor has good heat dissipation performance. Its cooling and ventilation system are driven by independent wiring. It can be forced to dissipate heat to ensure that the VSD motor can operate at different frequencies. The motor can generate heat and dissipate in time;
(2) The insulation performance of the VSD motor is good, and it can take in the impact that has on the VSD motor, from the different current and voltage of different frequencies.
5. It is not recommended to run the variable frequency motor at low frequency. After the motor runs at low frequency for a long time, it is particularly prone to heat generation, which will cause the motor to burn out. The best operating frequency of the motor is to work close to the constant operating frequency.
6. The frequency conversion range of the commonly used frequency converter is 1-400HZ; but in practical application, considering that the standard of the Chinese  motor is planned according to the power frequency of 50HZ, the application is in fact limited within the range of 20-50HZ.
Therefore, the minimum allowable frequency of the variable-frequency motor is related to the specific operating frequency range of the variable-frequency motor. Generally, the lowest value that the VSD motor allows can be taken.
II: the minimum operating speed of slurry pumps
Each slurry pump has its own performance curve, which specifies the minimum operating speed of the pump. Only when the speed is higher than the specified speed, the pump can operate normally. The frequency at this speed is the minimum operating frequency of the slurry pump.
Of course, there are other influences such as the flow rate of pipelines. Simply put, it can be considered that the above two points, that is, the frequency determined by the minimum speed of the slurry pump and the minimum operating frequency of the variable frequency motor are the two factors that affect the minimum operating frequency of the slurry pump. Among these two factors, the highest frequency value is the minimum operating frequency of the slurry pump.

This paper mainly explains the type, structure, and model of the ZJ series slurry pump in the slurry pump.
There are two types of ZJ slurry pumps. One is the ZJ type, which is a horizontal shaft single-stage single-suction centrifugal slurry pump; The other is the ZJL type, which is a vertical shaft single-stage single-suction centrifugal slurry pump.
Ⅰ. Structural characteristics and model of ZJ slurry pumps
1. Structural characteristics of ZJ slurry pumps
1) Pump End
The pump head of the ZJ slurry pump includes a pump shell, impeller, and shaft seal device. The pump head is connected with the base with bolts. As required, the water outlet position of the pump can be installed and used by rotating eight different angles at an interval of 45 °.
The pump shell of the ZJ slurry pump is a double-layer shell structure. The outer layer is metal pump casing (front pump casing and rear pump casing), and its material is usually cast iron or ductile iron; the inner layer is made of high chromium alloy cast iron (including volute, throat bush, and frame plate liner insert).
The impeller is composed of a front cover plate, rear cover plate, blade, and back blade. The blades are twisted, usually in the quantity of 3-6. The back blades are distributed on the outside of the front cover plate and the rear cover plate, usually in the quantity of 8. The impeller is made of high chromium alloy cast iron, and the impeller is connected with the shaft by a thread.
The shaft seal device has three types: expeller + packing combined seal, packing seal, and mechanical seal.
The combined seal type of expeller and packing consists of the stuffing box, expeller, lantern ring, packing, gland, and shaft sleeve.
The packing seal type is composed of the stuffing box, shaft spacer, lantern ring, packing, gland, and shaft sleeve.
The mechanical seal type consists of a stuffing box, shaft spacer, mechanical seal, gland, and shaft sleeve.
2) Pump Base
The pump base has two structures: horizontal split type and barrel type.
The split base is lubricated with thin oil, which is mainly composed of the base body, base cover, shaft, bearing box, bearing, bearing gland, retaining sleeve, nut, oil seal, water retaining plate, release collar, and other parts, as shown in Figure 1. 150ZJ and above pumps are also equipped with water cooling device.
The cylindrical base is lubricated with grease, which is mainly composed of the base body, bearing body, shaft, bearing, bearing top sleeve, bearing gland, oil seal, oil cup, water retaining plate, release collar, and other parts.
The barrel base is only applicable to pump types with small power of 200ZJ and below. At present, there are only three specifications: T200ZJ-A70, T200ZJ-A60, and T150ZJ-A60.
See Figure 1 for the specific structure of the ZJ pump.


Ⅱ. Structural characteristics and model of ZJL slurry pumps
1. Structural characteristics of ZJL slurry pumps
ZJL slurry pump is mainly composed of impeller, volute, rear guard plate, shaft sleeve, support, support plate, shaft, bearing, bearing body and other parts.
The impeller, volute, and rear guard plate are made of high chromium alloy cast iron. The impeller and shaft are connected by threads, and the volute, support and bearing body are connected by bolts. The pump shaft and motor can be driven directly by coupling or belt.
The bearing of the ZJL pump is lubricated with grease. This series of pumps are nonshaft seal pumps.
See Figure 2 for the specific structure of the ZJL pump.

The following safety information related to slurry pump operation and maintenance should be carefully followed and proper procedures followed to avoid personal injury and equipment damage. All statutory requirements related to this equipment must be complied with at all times.
Do not apply heat to the impeller hub or air intake to aid in impeller removal. Heating may cause impeller crushing, injury or equipment damage.
Do not run the pump at zero or very low flow for extended periods of time. Failure to follow this warning may result in overheating of the pump and evaporation of the pumped fluid, creating very high pressures. Such actions could result in serious personal injury or equipment damage.
Check drive motor rotation before installing drive belts or couplings. Incorrect motor rotation may result in personal injury or equipment damage.
Do not put very hot or very cold fluid into the pump at ambient temperature. Thermal shock can cause the wet end parts of the pump to break. Pumps must be considered rotating machinery and pressure vessels. All relevant safety precautions and procedures for this type of equipment should be followed during installation, operation and maintenance of the pump.
In the case of auxiliary equipment associated with the pump (e.g. motors, belts, drive couplings, reducers, variable speed drives, etc.) during installation, operation and maintenance, all relevant operating instructions should be consulted and recommended procedures should be followed.
If you have any needs for slurry pump and its accessories, please contact CNSME® (Slurry Pump Supplier from China)

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Dredger pump is specially designed for the excavation of silt, gravel, mud and other bottom mud material pump. Its main functions include:


Mud excavation: The dredger pump achieves the excavation and collection of mud by drawing in the bottom mud material and transferring it to the ship. This makes it possible to carry out underwater desilting and dredging projects in rivers, lakes, ports and other waters.


Mud transport: The dredger pump will be sucked into the bottom mud material after the internal treatment of the pump, through the pipeline or pump slurry pipe to the designated area, such as the treatment station, reclamation site. This helps clear the silt at the bottom of the water body and provides the materials needed for subsequent works.


Sediment treatment: Dredger pumps can be used to remove sediment in river beds, lake bottoms and ports, reduce siltation in waters, improve waterway conditions, and promote the restoration and protection of the ecological environment in waters.


In general, dredger pumps play a vital role in water dredging, dredging, sediment treatment and other projects, helping to maintain the water environment, promote waterway traffic and water ecological protection.