Single screw pump performance and structure First, the main performance parameters 1. Flow Single screw pump flow determines the size of the rotor and stator and pump speed. In each cross-section of the single- screw pump (Figures 1 and 2), the cross-sectional area of ​​the stator bore is 
The cross-sectional area of ​​the screw is 
.
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Figure 1 The geometry of the screw
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Figure 2 Pump sleeve geometry
The flow area of ​​the pump is the difference between the area of ​​the stator bore and the cross-section of the screw, which is 4eDR.
(1) The theoretical discharge volume Vth per revolution of the screw is the product of the flow area and the stator lead T, ie: Vth=4eDRT (1)
(2) The theoretical flow rate QVth is the product of the theoretical discharge volume and rotation speed for each revolution of the screw, ie: 
or 
Where e is the eccentricity of the center and axis of the screw section, in mm;
DR - the diameter of the round section of the screw, DR = 2R, mm;
T——The lead of spiral groove in the inner sleeve of the pump sleeve, mm;
n - pump speed (Table 1), r/min.
(3) Actual flow qV 
or 
In the formula, ηV—the volumetric efficiency of the pump, ηV=0.65~0.85. When the discharge pressure is low and the diameter DR of the screw section is large, take a large value.
2. Speed ​​n When the single screw pump speed n is determined according to the liquid viscosity, see Table 1.
Table 1 The speed range and liquid viscosity of the single screw pump
Viscosity /Pa•s
Applicable speed range ( r/min )
Newtonian liquid
Non-Newtonian liquid
10-3~1
10-3~10
1500~800
1~10
10~100
800~300
10~700
100~1000
300~100
> 700
> 1000
< 100
The speed of the single-screw pump can also be determined according to the axial flow velocity vgm (also called the relative average sliding speed between the rotor and the stator) of the liquid to be delivered in the pump working chamber, in particular to determine, especially in conveying the solid particles. When the liquid and the rotor or stator of the pump may be worn out, the pump speed must be determined by the value of vgm. See Appendix A of JB/T 8644-2007 "Single-Screw Pump" for details.
3. Discharge pressure The discharge pressure of a single-screw pump depends on the characteristics of the pump's discharge piping system. The pump's screw diameter and speed cannot change the discharge pressure of the pump. The discharge pressure of the single screw pump is the product of the pressure and lead that each stator lead length T can reach. In general, the discharge pressure per stator lead length can reach 0.3~0.6 MPa. In order to minimize the axial dimension of the pump, the discharge pressure p2 reached by the pump is usually p2 = 0.6 iT (MPa).
In the formula iT——The stator lead number of the pump, also can be called the pump's number of stages.
4. Efficiency η When the single screw pump is working, the rotor (screw) and the stator (pump cover) are in contact with each other, and there is relative slip. Therefore, the single screw pump has a large mechanical loss, and the efficiency of the pump is generally low. η= 50%~80%. Each pump with a larger volume of liquid is more efficient.
5. Service life The relative slip of the rotor and stator of the single screw pump will cause the wear of the rotor and the stator, mainly the wear of the stator. Therefore, the service life of the single screw pump is low. General requirements: When transporting clear water or liquids like clean water, the stator life is not less than 2000 hours.
6. Flow regulation Single screw pump can adjust the flow rate by changing the speed of the pump under the condition of keeping the discharge pressure unchanged. The flow rate of the pump is proportional to the rotation speed, so it can be used as a quantitative pump or a metering pump within a certain range.
Second, the structure Single-screw pump has two kinds of horizontal and vertical structure.
1. The horizontal single screw pump has many horizontal structures, and its structural layout is reasonable (Figure 3). The pump suction port and the suction chamber are at the shaft end of the pump. At this time, the seal pressure of the pump shaft seal is inhaled. Pressure, low sealing pressure, reduces the possibility of leaks. When the liquid to be transported has poor fluidity, a larger rectangular suction port can be used, and a screw feeder (Figure 4) can be added to the suction chamber to push the pumped liquid into the pump working chamber to help the pump. Inhale fluid.
Figure 4 Single-screw pump with feeder
1-stator; 2-screw (rotor); 3-spiral feeder
2. Vertical screw pump Vertical structure is mostly used for submerged and submersible single screw pumps.
(1) The submerged pump is immersed in the liquid, and the pump drive system of the motor, the speed reducer, the bearing housing is placed above the liquid surface, and the suction pipe mouth and the suction room are at the lower end of the screw. When the pump is working, the pipette mouth is located at the bottom of the pump, suitable for transporting the sediment at the bottom of the tank (pool), but the pump chamber and the drain pipe are located at the end of the pump shaft. The sealing pressure of the shaft seal is the discharge pressure of the pump. Increased sealing difficulty (especially when the discharge pressure of the pump is high). Submerged pump immersion depth, usually the pump's own length. When the discharge pressure is 2.4MPa, the immersion depth is 3~3.5m; when it is required to increase the immersion depth, it needs to use long-axis transmission, and the immersed depth can be rotated within 80m with a rigid shaft, and the depth can be increased (up to several hundred meters). Flexible shaft drive.
(2) The single screw submersible pump body and the motor and the universal joint are all submerged in the liquid to be delivered. The motor is placed under the pump. The motor and the pump are directly connected. The pump speed and the motor speed are the same. The pump is directly driven by the screw. The liquid is sucked by the end of the universal joint, and the liquid is discharged upward from the upper end of the screw. Therefore, the submersible pump has no long axis, which can save steel materials, and it does not need to use a shaft seal, and there is no leakage problem, but a special submersible motor is required. .
The depth of the submergible pump depends on the discharge pressure (head) of the pump. The submersible pump is not suitable for pumping sediments. It is generally used for pumping viscous crude oil in the oil field, and the submerged depth can reach 1000m.
(3) Screws Single-headed screw rods are generally circular in cross-section, and the stator holes are double-ended spiral holes, which are called 1-2 (or 1/2). The other type is 2-3 type (or 2/3 type). Its screw cross-section is an elliptical double-headed screw rod, and the stator hole is a three-headed spiral hole. The working volume of 2-3 type is increased by 45% than that of 1-2 type, and the flow rate is increased by 45% at the same rotation speed. At the same flow rate, the wear of the stator can be reduced and the service life can be improved. At present, more applications are still 1-2 type screw and pump sets.
The screw material is carbon steel, alloy steel and stainless steel, which can be manufactured by mechanical processing. The large-diameter screw adopts a hollow structure. Stators are mostly made of rubber, commonly used are: natural rubber (used to transport sewage, mud, organic coatings, etc.); NBR (for oil, medicine, food, cosmetics, etc.); fluoro rubber (for conveying Hydrocarbons, benzene, alkane solvents, etc.); Chlorosulfonated polyethylene rubber (used to transport acids, alkalis, oils, etc.) and urethane rubber.
Third, the main geometric parameters 1. Single screw pump screw diameter of the circular cross-section DR, eccentricity e, pitch t and electronic spiral hole cross-sectional dimensions and lead T (Figure 1 and Figure 2) is determined based on the flow required. When it is known that the liquid to be delivered and the required flow rate, according to the nature of the liquid being delivered, select the appropriate rotation speed (see Table 1); according to the required flow rate and the volumetric efficiency of the pump, determine the designed drainage volume for each revolution; The following relationship determines the DR, e, and T values, and is used in equation (1) to account for the design discharge volume for each revolution of the pump.
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When the discharge volume per revolution is 0.016L~16L, e=3~30 (large pump value), T=2t
2. The length L of the screw and pump sleeve of the single screw pump is determined according to the discharge pressure reached. The minimum length of the screw and pump sleeve should be greater than the axial length occupied by the two seal lines formed by the screw (ie, a seal chamber) to ensure that at least one seal line separates the suction and discharge ports at any instant. The minimum length Lmin of the screw and pump sleeve should be: Lmin = (1.2~1.5)T
The length L of the screw and pump sleeve is: L=iTT+(0.2~0.5)T
Where iT - number of stages (number of stator leads), iT = p2/0.6
Fourth, the performance of the conversion When the single-screw pump, double-screw pump, three-screw pump and five-screw pump test speed, viscosity and the specified value is different, the pump flow and power can be converted by the following formula.
1. Traffic .png)
Where qv0 is the measured flow rate when the discharge pressure is 0;
Qvi - Measured flow under measured discharge pressure;
n - the specified speed;
Ni - the measured rotational speed under the measured discharge pressure;
ν - the specified viscosity of the medium is generally 75mm2/s;
Îi - actual viscosity, mm2/s;
k - the conversion index, k = 0.25 when νi ≥ ν, k = 0.5 when νi < ν.
2. Power .png)
In the formula Pi - Measured power under measured discharge pressure, kW;
P0——measured power value when discharge pressure is 0, kW.
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