Questions and answers about dry screw vacuum pumps

1.What are the precautions for the test run of the dry screw vacuum pump?

Before the test run, check whether the maintenance quality meets the quality standards, and whether the records are complete and accurate; the cranking is light and free without jamming; the packing gland is not deflected, the leakage meets the requirements, and the inlet valve is opened to self-pressurize the pump and empty it.

When running with load, the operation should be stable, no noise, no vibration, the motor should not exceed the current, the medium flow and pressure should be stable, meet the nameplate requirements or meet the production needs, and the seal leakage should meet the requirements.

2.There may be the following reasons for the failure of the dry screw vacuum pump to measure:

1.If the suction pipeline is blocked or leaks, the suction pipeline should be checked;

2.The screw and the pump sleeve are worn out, repair or replace parts;

3.If the safety valve fails, adjust the spring, or grind and repair the disc and seat;

4.The motor is reversed or the speed is not enough, repair or replace the motor.

3. What are the requirements for disassembly, assembly and adjustment of the dry screw vacuum pump?

Disassemble the shaft seal and bearing lock nut, use light force to prevent damage to the thread; remove the connecting bolts between the bearing box and the pump body, remove the inner end cover, and then you can pump the screw. Use a special tool to pull the screw. Three or two The screws are withdrawn at the same time.

During assembly and adjustment, a little lubricating oil should be added to the contact part between the end face of the screw and the end cover, and between the screw and the bearing sleeve to prevent dry friction of these parts during the assembly process; fasten the outer end cover, bearing box and The connecting bolts of the pump body should be operated symmetrically, and the force should be even. Turn the screw while tightening.

4.What are the characteristics of the lipseal and sealing structure of the dry screw vacuum pump?

The shaft seal of the dry screw vacuum pump is generally designed as a rubber skeleton lip seal, which should be replaced every time it is overhauled. It is generally a lip-shaped seal ring made of nylon, polyethylene, etc., and has excellent wear resistance and pressure resistance. Working in an environment with poor shaft finish and slightly poor lubrication conditions, the suitable temperature is -70~+100°C, and the pressure is lower than 0.01MPa in oil, water and other media. The resilience of the sealing ring is poor, generally A traveler etc. is used to supplement the elastic force to enhance the sealing performance.

5.What are the technical standards for the dry screw vacuum pump maintenance?

The technical standards for screw pump maintenance are as follows:

1.See Table 1-1 for the fit clearance of each part of the screw pump;

2.The alignment error is 0.05~0.10mm;

3.The sealing leakage shall not exceed 10 drops per second.

Table 1-1

Fitting clearance of each part of the dry screw vacuum pump

Project Reference data
Gap between screw tooth top and housing/mm 0.14~0.33
Clearance between tooth top and dedendum when the screw meshes/mm 0.14-0.33
Normal section side clearance/mm 0.12-0.25
Clearance between bearing outer ring and gland at gearbox end/mm 0.02~0.06
Coordination of rolling bearings and shafts H7/k6
Coordination of rolling bearings and bearing housings H7/h6

6.The main reasons for the vibration of the dry screw vacuum pump are as follows:

(1). If the pump and the motor are not concentric, they should be re-aligned and the concentricity adjusted.

(2). The screw and the pump casing are not concentric or the gap between the two is too large, which needs to be repaired and adjusted.

(3). For air intake in the pump, the suction pipeline should be repaired to eliminate the leaking parts.

(4). If the installation height is too large, cavitation will occur in the pump, so the installation height should be lowered or the speed should be reduced.

7.List of common faults and treatment methods of the dry screwvacuum pumps

This paper elaborates in detail the failure phenomenon of screw pumps (including twin-screw pumps and three-screw pumps), the reasons for the failure of screw pumps, and the treatment methods.

NO. Fault Phenomenon The reason Processing method
1 The pump does not suck oil 1. The suction pipe is blocked or leaking

2. The suction height exceeds the allowable suction vacuum height

3. The motor reverses

4. Medium viscosity is too high

1. Overhaul the suction pipeline

2. Reduce the suction height

3. Change the direction of the motor

4. Warm the medium

2 The pointer of the pressure gauge fluctuates greatly 1. Suction pipeline leaks

2. The safety valve is not adjusted properly or the working pressure is too high so that the safety valve is sometimes opened and sometimes closed

1. Overhaul the suction pipeline

2. Adjust the safety valve or reduce the working pressure

3 Traffic drop 1. The suction pipe is blocked or leaking

2. Screw and pump sleeve wear

3. The spring of the safety valve is too loose or the contact between the disc and the seat is not tight

4. The motor speed is not enough

1. Overhaul the suction pipeline

2. Parts should be replaced when the wear is serious

3. Adjust the spring, grind the disc and seat

4. Repair or replace the motor

4 A sharp increase in shaft power 1. The discharge pipe is blocked

2. Serious friction between the screw and the pump sleeve

3. The viscosity of the medium is too high

1. Stop the pump to clean the pipeline

2. Overhaul or replace relevant parts

3. Heat up the medium

5 The vacuum pump vibrates greatly 1. The pump and the motor are not concentric

2. The screw and the pump sleeve are not concentric or the gap is large

3. There is air in the pump

4. The installation height is too large, causing cavitation in the pump

1. Adjust concentricity

2. Maintenance and adjustment

3. Overhaul the suction pipeline and eliminate the leaking parts

4. Reduce the installation height or reduce the speed

6 Pump heat 1. Severe friction inside the pump

2. The oil return hole of the mechanical seal is blocked

3. The oil temperature is too high

1. Check and adjust the screw and pump sleeve

2. Unclog the oil return hole

3. Properly lower the oil temperature

7 The large amount of oil leakage from mechanical seal 1. The assembly position is wrong

2. The sealing gland is not flattened

3. The sealing surface of the moving ring or the static ring is damaged

4. The dynamic ring or static ring seal ring is damaged

1. Re-install as required

2. Adjust the sealing gland

3. Grind the sealing surface or replace it with a new one

4. Replace the sealing ring

8.The dismantling and overhaul of the dry screw vacuum pump are as follows:

(1). Check the cylinder liner Babbitt alloy. If the gap between the cylinder liner and the screw exceeds the standard, the cylinder liner should be recast with Babbitt alloy.

(2). Overhaul the screw to ensure that the surface of the screw is smooth and free of burrs.

(3). For the maintenance of the copper sleeve, the copper sleeve and the screw shaft are well matched, and the turning should be easy and free, otherwise the copper sleeve and copper sleeve should be ground, or the inner wall of the cylinder liner should be scraped to make it meet the requirements.

(4). For the inspection and maintenance of the lip seal, the packing should be properly selected and the filling method is correct. If the shaft seal is a mechanical seal, it should be inspected and repaired according to the corresponding requirements.

(5). For centering and alignment, clamp the dial indicator on the alignment frame, then fix the alignment frame on the backrest wheel, and mark the pointer on the outer diameter of the other backrest. The error should be within the specified range, generally 0.05 ~0.10mm.

(6). Test run, stable operation, no noise, no abnormal vibration, no overcurrent, stable flow and pressure, meeting production needs, it is qualified.

9.Types of screw pumps and their comparison list

This paper analyzes in detail the differences between single screw pumps, twin screw pumps and three screw pumps, as well as their respective advantages and disadvantages and application occasions from four aspects of the structure, characteristics, performance parameters and application occasions of the screw pump.

Type Structure Features Performance parameters Applications
Single screw vacuum pump Single head male helical rotor

in a special double-headed pussy

Eccentricity in the helical stator

grass screw tired

ground rotation (the stator is flexible

soft), can be along the pump

Heart line swings back and forth, with

The stator is always engaged


1.Can transport liquid containing solid particles

2.It can be used for fluids of almost any viscosity, especially for high viscosity and non-Newtonian fluids

3. The working temperature is limited by the stator material


Flow up to 150m&gup3:/h;

pressure up to 20MPa


Used in molasses, fruit pulp, starch paste, chocolate paste, paint, tar, paraffin, grease,Mud, clay, clay, etc.


Two-screw vacuum pump There are two screw shafts of the same size, one is the driving shaft and the other is the driven shaft, and the synchronous rotation is achieved through gear transmission


1.There is a gap of 0.05~0.15mm between the screw and the pump body, as well as the screw, so that the wear is small and the service life is long

2.The stuffing box is only affected by the suction pressure and the leakage is small

3.Compared with the three-screw pump, it is not sensitive to impurities

The pressure is generally about 1.4MPa, the maximum for viscous liquid is 7 MPa, the liquid with low viscosity can reach 3MPa, the flow rate is generally 6~600m&aup3:/h, the maximum 1600 m&sup3:/h liquid viscosity should not exceed 1500mm²/s


For lubricating oil, grease, crude oil, asphalt, fuel oil and other highly viscous oils


Three-screw vacuum pump Consists of a driving screw and two driven screws meshing with it


1.The driving screw directly drives the driven screw without gear transmission, and the structure is simple

2.The pump body itself is used as the bearing of the screw, so there is no need to install radial bearings

3.The screw does not bear bending load and can be made very long, so high pressure can be obtained

4.It is not suitable to transport liquids containing more than 600m solid impurities

5. It can run at high speed, which is a kind of small and large flow

Pressure up to 70MPa, flow up to 2000m&sup3:/h. Suitable for media with a viscosity of 5~250mm²/s


It is suitable for conveying lubricating oil, heavy oil, light oil and crude oil, etc. It can also be used to transport and pressurize high-viscosity liquids such as dry glycerin and viscose


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