双螺杆泵的选型技巧
性能参数的选择：
Performance parameters of choice:
1.流量Q：
1. Flow rate Q:
作为容积式泵，影响双螺杆泵流量的因素主要有转速n，压力p，以及介质的粘度v。
As a positive displacement pump, the factors that affect the twin-screw pump flow main speed n, the pressure p, as well as the medium viscosity v.
1.1 转速 n 的影响：
1.1 Speed n impact:
螺杆泵在工作时，两螺杆及衬套之间形成密封腔，螺杆每转动一周便由进口向出口移出一个密封腔，即一个密封腔的体积的液体被排出去。理想状态下，泵内部无泄漏，那么泵的流量与转速成正比。即：
Screw pump at work, the two form a seal between the screw and the bushing cavity, screw each week, turning it from import to export out of a sealed chamber, namely, the volume of a sealed chamber to the liquid being discharged. Ideally, the internal pump leak, then the pump is proportional to the flow and speed. Namely:
Qth=n*q
Qth = n * q
n----转速；
n ---- rotational speed;
q----理论排量，即泵每转一周所排出的液体体积；
q ---- theory of displacement, that is, transfer pumps for each week of the emission of liquid volume;
Qth----理论排量。
Qth ---- theory of displacement.
1.2 压力△P的影响：
1.2 Pressure △ P impact:
泵实际工作过程中，其内部存在泄漏，也称滑移量。由于泵的密封腔有一定的间隙，且密封腔前、后存在压差△P，因此，有一部分液体回流，即存在泄漏，泄漏量用△Q表示，则
Pump actual work process, their internal leakage there is, also known as slippage. As the pump seal chamber has a certain gap, and the sealed chamber before and after the existence of differential pressure △ P, therefore, some of the liquid return, that is, there is leakage, leakage with △ Q, said the
Q=Qth-△Q
Q = Qth-△ Q
显而易见，随着密封腔前、后压差△P升高，泄漏量△Q逐渐增大。对于不同型线和结构，影响大小也各不相同。
Obviously, with the sealed chamber before and after the pressure difference △ P rise, leakage △ Q is gradually increasing. For the different types of lines and structures, affecting the size of different.
1.3 粘度v的影响：
1.3 Viscosity v of the impact:
试想：将清水和粘稠的浆糊以相同的体积从漏斗式的容器中泄漏出去。显然水比浆糊要泄漏得快。
Consider: The water and viscous paste in the same volume of container from the funnel-type leak. Obviously the water to leak faster than the paste.
同理，对于双螺杆泵，粘度大的流体比粘度小的液体的泄漏要小，泄漏量与介质粘度有一定的比例关系。
Similarly, for the twin-screw pump, the fluid viscosity smaller than the viscosity of the liquid leakage is smaller, leakage volume and viscosity of a certain percentage of media relations.
综上所述，要综合地考虑以上各种因素，通过一系列的计算才能精确地知道泵的实际流量是否符合工况要求。
To sum up, we should consider these factors in an integrated manner, through a series of calculations in order to accurately know the actual flow of the pump meets required conditions.
2.压力△P：
2. Pressure △ P:
与离心泵不同，双螺杆泵的工作压力△P由出口负载决定，即出口阻力来决定。出口阻力与泵的出口处的压力是匹配的，出口阻力越大，工作压力也越大。若想知道压力，则需要用流体力学的知识对出口阻力精确的计算。
With the centrifugal pump is different twin-screw pump working pressure △ P export-load decision that the export of resistance to decide. Export resistance and the pump outlet pressure is matched, export the resistance the greater the greater the work pressure. If you want to know the pressure, you need to export the knowledge of fluid mechanics resistance calculations.
3.轴功率N：
3. Shaft power N:
泵的轴功率分为两部分，即：
The pump shaft power is divided into two parts, namely:
Nth----液压功率，即压力液体的能量；
Nth ---- hydraulic power, that is, the pressure energy of the liquid;
Nr----摩擦功率。
Nr ---- friction power.
对于确定的压力和流量，其液压功率是一定的，因此影响轴功率的因素为摩擦率Nr。
For determining the pressure and flow, the hydraulic power is certain, therefore shaft power of the factors affecting the friction rate of Nr.
摩擦功率是由于运动部件的摩擦而消耗的那部分功率。这些摩擦功率显然是随着工作压差的增加而增加的，并且介质粘度的增加也会引起液体摩擦功率的增加。
Friction power is due to friction of moving parts of that part of the power consumed. The friction power is clearly increased as the work pressure increased, and the media can also cause an increase in viscosity of the liquid friction power increases.
由此，泵的轴功率除了液压功率外，其中摩擦功率随介质粘度及工作压力而增加，因此在选择配套电机时，介质的粘度也是一个非常重要的参考数据。尤其在输送高粘度介质时，需要作比较精确的计算。
As a result, the pump shaft power In addition to hydraulic power, the friction power as a medium in which the viscosity and pressure increase, and therefore choose matching motor, the medium viscosity is also a very important reference. Particularly in the transport of high viscosity medium, you need to make more precise calculations.
在计算功率后，选择配套电机时应遵照样本表格中所规定的有关规定。
In calculating the power, select the auxiliary motor should be in accordance with the form set forth in the sample of the relevant provisions
N(KW) N≤10 10＜N≤50 N＞50 N＞100
K 1.5 1.25 1.15 1.1
N (KW) N ≤ 10 10 <N≤50 N> 50 N> 100
K 1.5 1.25 1.15 1.1
Nm=N.K
Nm = N.K
Nm----电机功率 N----轴功率 K----功率储备系数
Nm ---- Power N ---- shaft power coefficient K ---- Power Reserve
4.吸上性能的计算及选择
4. Suction performance computing and select
泵工作分为以下几个阶段：
Pumps work is divided into the following phases:
4.1 吸入，此时液体连续不断地沿吸入管道移动；
4.1 inhalation, this time along the suction pipe of liquid continuous movement;
4.2 旋转的螺杆把能量传给工作液体；
4.2 rotating screw to pass the energy working liquid;
4.3 压出，此时液体带有克服压出管道系统所有阻力所必需的压力从泵中排出。
4.3 Press out the liquid at this time to overcome the pressure out of pipeline systems with all the necessary resistance to the pressure from the pump discharge.
在以上三个阶段中，为重要的阶段是必须保证泵的吸上条件，泵才能正常工作，这是泵工作的重要条件，否则就会发生气蚀，即引起振动，噪音等问题。
In the above three phases, the most important stage is the need to ensure that the conditions of the pump-priming the pump to work properly, this is an important condition for pump work, otherwise cavitation will occur, that is caused by vibration, noise and other issues.
5.汽蚀余量的计算：
5. NPSH calculation:
泵的汽蚀余量NPSHr与泵的转速n，导程h以及泵所输送介质的粘度v等因素都有关系，对我厂引进的Bornemann双螺杆泵用以下公式计算：
Pump NPSH NPSHr and pump speed n, lead h and the viscosity of the medium transport pumps and other factors, the relationship between v, to our factory introduced Bornemann twin-screw pump with the following formula:
NPSHr=(1.5+0.253VF 1.84345+0.0572VF 1.55)*v 0.4146
NPSHr = (1.5 +0.253 VF 1.84345 +0.0572 VF 1.55) * v 0.4146
VF----轴向流速，VF=n*h/60(m/s)；
n----转速(r/min)；
h----导程(m)；
v----工作粘度(°E)。
VF ---- axial velocity, VF = n * h/60 (m / s);
n ---- Speed (r / min);
h ---- Lead (m);
v ---- Work viscosity (° E).
由此可见，泵的NPSHr是随VF，v的增大而增大。因此在吸入条件不好的情况下，宜选择小导程的双螺杆泵。这在选型时是很重要的。
This shows that the pump is NPSHr with VF, v's increases. Therefore, in the case of inhalation are poor, should choose a small lead of the twin-screw pump. This is when the selection is very important.
5.1 装置汽蚀余量NPSHa的计算，这里不再阐述。
5.1 Device NPSHa NPSH calculations, this is no longer described.
5.2 想要保持泵正常工作，即不发生汽蚀、振动等问题，必须保证以下条件：
5.2 want to maintain the pumps to work, that is, cavitation does not occur, vibration and so on, must ensure that the following conditions:
NPSHa＞NPSHr 这即是泵的吸入条件。
NPSHa> NPSHr This means that the pump suction conditions.
6.双螺杆泵的转速选择：
NPSHa> NPSHr This means that the pump suction conditions.
选择不同的转速常牵涉以下问题：
Select a different speed often involves the following questions:
6.1 通过选择合适的泵转速，以达到适当的性能参数如流量等。
Select a different speed often involves the following questions:
6.2 随着粘度的不同，泵的转速亦应有所改变。
6.2 As the viscosity of the different pump speed should be changed.
对于Boremann双螺杆泵，粘度的变化是决定转速的主要条件，随着粘度的增大，允许转速也越低。
For Boremann twin-screw pump, the viscosity change is to determine the speed of the main conditions, with the viscosity increases, allowing the lower the speed.
转速的选择实质也是吸上性能的问题，尤其是在高粘度的情况下，如果转速选得过高，就会引起吸入不足，从而产生噪音和振动等问题。因此务必遵照有关原则选择转速。
Speed is also a choice of smoking on the performance of real problems, especially in high-viscosity case, if the speed of the election are too high, they cause less inhalation, resulting in noise and vibration issues. So be sure to comply with the principle of selection speed.
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