Procurement of constant flow overflow pump

HLCB-D seriesConstant flow overflow pump

The HLCB-D series constant flow relief pump is a combination of an external gear pump with automatic axial clearance compensation and a constant flow relief valve. This series of products has small external dimensions, simple structure, and good processability. Mainly used for hydraulic power steering systems in agricultural machinery and industrial vehicles, providing constant flow to ensure safe, reliable, and stable operation of the system.

Working principle of wheel pump

The concept of a gear pump is very simple, that is, its most basic form is two gears of the same size meshing and rotating with each other in a tightly fitting housing. The interior of this housing is similar to an "8" shape, with two gears installed inside. The outer diameter and sides of the gears are tightly fitted with the housing. The material from the extruder enters the space between two gears at the suction port and fills it. It moves along the shell with the rotation of the teeth and is finally discharged when the two teeth mesh. In terms of terminology, gear pumps are also known as positive displacement devices, which are like pistons in a cylinder. When one tooth enters the fluid space of another tooth, the liquid is mechanically squeezed out. Because liquids are incompressible, liquids and teeth cannot occupy the same space at the same time, thus eliminating liquids. Due to the continuous meshing of the teeth, this phenomenon occurs continuously, thus providing a continuous discharge at the pump outlet. The amount discharged is the same for each rotation of the pump. As the drive shaft rotates continuously, the pump also continuously discharges fluid. The flow rate of a pump is directly related to its rotational speed. In fact, there is a small amount of fluid loss inside the pump, which prevents the pump's operating efficiency from reaching 100%. This is because these fluids are used to lubricate the bearings and gears on both sides, and the pump body cannot fit seamlessly. Therefore, it is impossible to discharge the fluid 100% from the outlet, so a small amount of fluid loss is inevitable. However, the pump can still operate well and achieve an efficiency of 93% to 98% for most extruded materials.

For fluids with changes in viscosity or density during the process, this pump will not be greatly affected. If there is a damper, such as placing a filter or a limiter on the discharge side, the pump will push the fluid through them. If the damper changes during operation, that is, if the filter becomes dirty, clogged, or the back pressure of the limiter increases, the pump will still maintain a constant flow until it reaches the mechanical limit of the weakest component in the device (usually equipped with a torque limiter). There is actually a limit to the speed of a pump, which mainly depends on the process fluid. If oil is being transported, the pump can rotate at a high speed. However, when the fluid is a high viscosity polymer melt, this limit is greatly reduced. It is very important to push high viscosity fluid into the two tooth space on one side of the suction port. If this space is not fully filled, the pump cannot discharge accurate flow, so PV value (pressure x flow rate) is also another limiting factor and a process variable. Due to these limitations, gear pump manufacturers will offer a range of products in different specifications and displacements (the amount discharged per revolution). These pumps will be matched with specific application processes to achieve optimal system capacity and price.

The structural characteristics of gear pumps: The gears adopt a new technology with international advanced level of 90 years - double arc sine curve tooth profile arc. Compared with involute gears, its most prominent advantage is that there is no relative sliding of the tooth profile during the gear meshing process, so there is no wear on the tooth surface, balanced operation, no trapped liquid phenomenon, low noise, long service life, and high efficiency. This pump breaks free from the constraints of traditional design, allowing gear pumps to enter a new field in design, production, and use. The pump is equipped with a differential pressure safety valve as overload protection, and the full reflux pressure of the safety valve is 1.5 times the rated discharge pressure of the pump. It can also be adjusted according to actual needs within the allowable discharge pressure range. However, this safety valve cannot be used as a pressure reducing valve for long-term operation, and can be installed separately on the pipeline if necessary. The pump shaft end seal is designed in two forms, one is mechanical seal and the other is packing seal, which can be determined according to specific usage and user requirements.

Operation and maintenance of gear pump

1. Start:

(1) Before starting, check the sealing of all pipeline flanges and joints.

(2) Drive the coupling without friction or collision noise.

(3) The first start-up should inject the conveying liquid into the pump.

(4) Before starting, the valves in the suction and discharge pipelines should be fully opened, and closing the valves for starting is strictly prohibited.

(5) After verifying the direction of motor rotation, start the motor.

2. Parking:

(1) Turn off the electric motor.

(2) Close the inlet and outlet valves of the pump.

Common faults of gear pumps

The pump cannot discharge the material

(1) Fault phenomenon: The pump cannot discharge the material

Reason for malfunction: a. Reverse rotation direction; b、 The suction or discharge valve is closed; c、 No material or low pressure at the inlet; d、 The viscosity is too high, and the pump cannot bite the material

Countermeasure: a. Confirm the direction of rotation; b、 Confirm if the valve is closed; c、 Check valves and pressure gauges; d、 Check the viscosity of the liquid and whether there is a flow rate proportional to the speed when running at low speed. If there is a flow rate, it indicates insufficient inflow

Insufficient pump flow

(2) Fault phenomenon: Insufficient pump flow

Reason for malfunction: a. The suction or discharge valve is closed; b、 Low inlet pressure; c、 Blockage of export pipeline; d、 Leakage of packing box; e、 Low speed

Countermeasure: a. Confirm if the valve is closed; b、 Check if the valve is open; c、 Confirm if the discharge volume is normal; d、 Fastening; When a large amount of leakage affects production, the operation should be stopped and disassembled for inspection; e、 Check the actual speed of the pump shaft;

Abnormal sound

(3) Fault phenomenon: abnormal sound

Reason for malfunction: a. Large eccentricity or poor lubrication of the coupling b. Motor malfunction; c、 Abnormal gearbox; d、 Poor installation at the shaft seal; e、 Shaft deformation or wear

Countermeasure: a. Correct or fill with lubricating grease; b、 Check the electric motor; c、 Check the bearings and gears; d、 Check the shaft seal; e、 Parking disassembly inspection

excessive current

(4) Fault phenomenon: Excessive current

Reason for malfunction: a. High outlet pressure; b、 Excessive viscosity of the melt; c、 Poor assembly of shaft seal; d、 Wear of shaft or bearing; e、 Motor failure

Countermeasure: a. Check downstream equipment and pipelines; b、 Test viscosity; c、 Check the shaft seal and adjust it appropriately; d、 After parking, check if the hand cranked vehicle is too heavy; e、 Check the electric motor

泵突然停止

(5) Fault phenomenon: The pump suddenly stops

Reason for malfunction: a. Power outage; b、 Motor overload protection; c、 Coupling damage; d、 Excessive export pressure, interlocking reaction; e、 Abnormal biting inside the pump; f、 The shaft and bearing are stuck due to adhesion

Countermeasure: a. Check the power supply; b、 Check the electric motor; c、 Open the safety cover and conduct a turning inspection; d、 Check the instrument interlocking system; e、 After parking, confirm the front and rear turntables; f、 Confirmation of turning gear

Sealing oil leakage

(6) Fault phenomenon: Sealing oil leakage

Cause: a. The shaft seal was not adjusted properly, b、 The sealing ring is worn and the gap is thin and large, c、 The friction surfaces of the dynamic and static rings of the mechanical seal are damaged, and the spring is loose

Countermeasure: a. Adjust b. Tighten the gland bolts appropriately or replace the sealing ring, c、 Replace the dynamic and static rings or re grind them,

4、 Replace the spring and observe other phenomena

1. Cause of occurrence

① The tooth clearance between the inner and outer rotors is too large, causing the suction oil chamber to communicate with each other. The volumetric efficiency is significantly reduced, and the output flow rate is insufficient;

② The axial clearance is too large;

③ The sealing at the joint surface in the oil suction pipeline is not tight, which causes the pump to suck in air and reduces the effective suction flow rate;

④ Poor oil absorption, such as a decrease in suction flow due to excessive viscosity of the oil or blockage of the oil filter by dirt;

⑤ The overflow valve is stuck in the half open position, and a portion of the flow from the pump returns to the oil tank through the overflow valve, resulting in insufficient flow into the system. At this time, a system pressure failure occurs.

2. Exclusion method

① Replace the inner and outer rotors to ensure that the backlash is within the specified range (generally less than 0.07mm);

② Grind the two end faces of the pump body to ensure that the axial clearance between the inner and outer rotors is within the range of 0.02~0.05mm after assembly;

③ Replace the damaged oil suction pipe seal, wrap the threaded part of the pipe joint with polytetrafluoroethylene tape, and then tighten the pipe joint;

④ Select oil with appropriate viscosity and clean the oil inlet filter to ensure smooth oil suction. And increase the diameter of the oil suction pipe as appropriate;

⑤ Repair the overflow valve and eliminate the phenomenon of the overflow valve partially short circuiting the oil tank, which causes a decrease in the effective flow rate of the pump.