由于各螺杆(gǎn)的(de)相(xiàng)互齧合以及螺杆與(yǔ)襯筒内壁(bì)的緊密配合，在泵(bèng)的吸入口和排出口之間，就會被(bèi)分(fèn)隔成(chéng)一個或多個(gè)密封空間。随着(zhe)螺杆的轉動和齧合，這些密封空間在(zài)泵的吸入端不斷形成，将吸入室中的液體封入(rù)其中，并自吸入室沿(yán)螺杆軸向連續(xù)地推移至排出端，将封閉(bì)在 各空間中的(de)液體不斷排出，猶如一螺母在螺紋回轉時被不斷向前推進的情形那樣，其中螺紋圈數看做液體，當螺釘(dìng)旋轉時螺紋在轉動時(shí)就相當于液體在螺杆泵裡面的情形(xíng)，這就是螺(luó)杆泵的基本工作(zuò)原(yuán)理(lǐ)。螺杆與殼體之間的密封面是(shì)一個空間曲面。在這個曲面上存在着(zhe)諸如ab或de之類的非密封區，并且與螺杆的(de)凹槽部分形成許多三角(jiǎo)形的(de)缺口abc、def。這些三角形 的缺口構(gòu)成液體的通道，使主動(dòng)螺杆凹槽A與從動螺(luó)杆上的凹槽B、C相連通(tōng)。而凹槽B、C又(yòu)沿着自己的螺線繞向背面， 并(bìng)分别和背面的凹槽(cáo)D、E相連通。由于在槽D、E與(yǔ)槽F(它屬于另一頭螺(luó)線)相銜(xián)接的密封面上，也存在着類(lèi)似于正面的三角(jiǎo)形缺口a’b’c’，所以D、F、E也将相通。這樣(yàng)，凹槽ABCDEA也就(jiù)組成一個“∞” 形的密封(fēng)空間(如采用單頭螺紋，則凹槽将順軸(zhóu)向盤饒螺(luó)杆(gǎn)，将吸排口貫通(tōng)，無法形成密(mì)封)。不難想象，在這樣的(de)螺杆 上，将形成許(xǔ)多個獨立的“∞”形密封空間，每一個密封空間所占有的(de)軸向長度恰好等于累杆的導(dǎo)程t。因此，為了使螺杆能吸、排油口分隔開來，螺杆的螺紋段的長度至少要大(dà)于一(yī)個導程。Due to the mutual engagement of each screw and screw and the close coordination of the liner wall, between the inlet and outlet of the pump, can be divided into one or more of the sealed space.With the rotation of the screw and the meshing, the sealed space in pump suction side form unceasingly, the liquid from the suction chamber seal in among them, and the suction chamber along the screw axial continuously goes on to the discharge end, will be closed in the space of the liquid discharge, like a nut in screw rotation being constantly move forward, the screw thread turns as liquid, when screw rotating screw rotation is equivalent to the liquid in the inside of the screw pump, this is the basic work principle of screw pump.The sealing surface between screw and shell is a space curved surface.Exist on the surface of the sealing section, such as ab or DE and screw groove part of the form many the gap of the triangle ABC, def.These triangular gap formation fluid channels, make active screw groove with A driven screw groove on the connected to B and C.And groove B, C and along their spiral around to the back, and, respectively, and on the back of the groove connected to D and E.Due to the tank D, E and F (it belongs to another head spiral) of corresponding seal surface, there are also similar to the positive triangle gap a 'b' c ', so D, F, E will also is same.So, grooves ABCDEA on forming a "up" form of the sealed space (such as using single thread, axial disc groove will arrange spare screw, connecting the suction PaiKou, unable to form a seal).It is not hard to imagine that in this kind of screw, will form a number of independent "up" form sealed space, each of the sealed space occupied the axial length equals the tired stem lead t.Therefore, in order to make the screw suction and discharge of oil can be separated, the length of the screw thread of at least than a lead.