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對于外置軸承的雙螺桿泵，通過軸承定位兩根螺桿在襯套中互不接觸，齒側之間保持恒定的間隙(其間隙值由工況及泵本身規格決定)，螺桿外圓與襯套內圓面也保持恒定的間隙不變。兩根螺桿的傳動由同步齒輪完成。齒輪箱中有獨立的潤滑，與泵工作腔隔開。這種結構的優點大大拓寬了雙螺桿泵的使用范圍，即除了輸送潤滑性良好的介質外,還可輸送大量的非潤滑性介質,各種黏度(最高黏度可達3x 10° mm2/s)的介質以及具有腐蝕性(酸、堿等性質)、液計磨蝕性的液體。雙螺桿泵由于其恒定間隙的存在以及型線上的特點,其屬于非密封型容積泵，因此除了輸送純液體外，還可輸送氣體和液體的混合物，即氣液混輸,這也是雙螺桿泵非常獨特的優點之一。 雙螺桿泵由于結構的獨特設計，可以自吸而無需專門的自吸裝置，而且由于軸向輸送軸流速度較小而具備很強的吸上能力，即很小的NPSH,值。雙螺桿泵還可干轉。由于運動部件在工作時互不接觸，因此短時的干轉不會破壞泵元件，這種特點給自動控制的流程提供了極大的方便。但干運轉時間受多種因素限制，一般很短。
2)三螺桿泵
    三螺桿泵的內部由一根主動螺桿、兩根從動螺桿和包容三根螺桿的襯套組成密封腔，腔內的液體隨著螺桿的旋轉做軸向移動,達到輸送液體的目的。該泵的特殊結構保證了主從桿不受徑向力的作用,軸向力采用液壓平衡，軸承只承受螺桿的自重及很小的剩余軸向力，從動桿插入平衡套(平衡套起平衡軸向力的作用，又作滑動軸承使用)， 螺桿的幾何尺寸保證主桿到從桿不傳遞扭矩。從動桿是由輸送液體的壓力作用而旋轉的，從而保證了三螺桿具有很長的使用壽命和較高的機械效率，完美的線型設計及加工工藝，使各密封腔完全隔開，從而具有較高的容積效率。
    三螺桿泵在油庫和泵站中常作為輔助用泵來輸送潤滑油及中等黏度的原油，油氣混輸用YZ液下渣漿泵

For the twin-screw pump with external bearing, the two screws are not in contact with each other in the bushing through the bearing positioning, and a constant clearance is maintained between the tooth sides (the clearance value is determined by the working conditions and the pump specifications), and the clearance between the screw outer circle and the inner circle of the bushing is also kept constant. The transmission of two screws is completed by synchronous gear. There is independent lubrication in the gearbox, which is separated from the pump working chamber. The advantages of this structure greatly broaden the scope of application of the twin-screw pump, that is, in addition to conveying the medium with good lubricity, a large number of non lubricating media, media with various viscosities (up to 3x10 ° mm2 / s) and corrosive (acid, alkali, etc.) and abrasive liquids of the liquid meter can be transported. Due to the existence of constant clearance and the characteristics of profile line, twin-screw pump belongs to non sealed positive displacement pump. Therefore, in addition to conveying pure liquid, it can also transport gas and liquid mixture, that is, gas-liquid mixed transportation, which is one of the unique advantages of twin-screw pump. Due to the unique design of the structure, the twin-screw pump can self-priming without special self-priming device. Moreover, due to the small axial flow speed of axial transportation, it has strong suction capacity, that is, very small NPSH. The twin screw pump can also run dry. Because the moving parts do not contact each other during working, the short-term dry running will not damage the pump components, which provides great convenience for the automatic control process. But the dry running time is limited by many factors, which is usually very short.

2) Three screw pump

The inner part of the three screw pump consists of a driving screw, two driven screws and a bushing containing three screws. The liquid in the cavity moves axially with the rotation of the screw to achieve the purpose of conveying liquid. The special structure of the pump ensures that the master-slave rod is not affected by radial force. The axial force is balanced by hydraulic pressure. The bearing only bears the dead weight of the screw and a small residual axial force. The driven rod is inserted into the balance sleeve (the balance sleeve plays the role of balancing the axial force and is also used as a sliding bearing). The geometric size of the screw rod ensures that no torque is transmitted from the main rod to the slave rod. The driven rod is rotated by the pressure of conveying liquid, so as to ensure that the three screw has a long service life and high mechanical efficiency. The perfect linear design and processing technology make each sealing cavity completely separated, thus having high volumetric efficiency.

Three screw pumps are often used as auxiliary pumps to transport lubricating oil and medium viscosity crude oil in oil depots and pumping stations. YZ submerged slurry pump is used for oil-gas mixed transportation