多吸头排污泵的流量与扬程大小
    液环真空泵的排气量是指泵出口为大气压状态(760mHg)时单位时间内通过泵进口的吸入状态下的气体容积(m3/min),也称为抽气速率。

排气量取决于叶片间容积在与进气孔口脱离接触时容积的大小，即基元容积的大小。一般基元容积达到最大值时与进气孔口脱离，故排气量可按式(2-13)计算：

实际上,液环泵的排气量与真空度有关。每设计生产一种新结构的真空泵,在制造厂必须进行性能试验,作出性能曲线，表示出各种真空度下所能得到的抽气量及所消耗的功率，以备使用者选用。图2-12是SZB-4和SZB-8型水环真空泵的性能曲线。

极限真空度及最大排出压力

极限真空度是指液环泵排气量为零时的真空度，也可用残余压力表示(残余压力=大气氏-真空度)，残余压 力即绝对压力。因为容器中的压力不可能无限降低，当进 气压力低于某一值后，由于泵中液体发生气化，或是由于高压侧漏回的气量等于真空泵的抽气量或由于真空泵压力比过高而容积系数为零，都会使真空泵无法继续吸入新鲜气体，容器中压力也不可能再下降。以15C的水作密封液时，单级泵残压可达30mm汞柱(约4000Pa),两级泵残压可达15mmHg(约2000Pa);与喷射泵串联使用，残压可达2~5mmHg (267~667Pa)。
四、真空泵的使用示例
图2- 13为油库常用的真空系统流程,其作用是:

(1)使离心泵和吸入管路充满所输油品。

(2)抽吸油罐车底油。

(3)当夏季气温高时，可利用真空卸油造成虹吸。

该真空系统由真空泵，真空能，气水分离器和管路组成。一般采用水环真空泵得到所需的真空度。为了保证真空泵内形成水环和循环冷却，在真空泵的排出管线上串装了一个气水分离器。为了保证真空泵的操作平稳可靠并防止油品进入真空泵，在真空泵的吸入管路上设置真空罐。真空错连接离心泵，是为了抽净泵和它 的吸入管线中的空气，使它们充满油，以进行灌泵。真空罐连通鹤管是为了造成虹吸现象抽吸底油。多吸头排污泵的流量与扬程大小.

Flow and head of multi suction sewage pump

The exhaust volume of liquid ring vacuum pump refers to the gas volume (m3 / min) under the suction state through the pump inlet in unit time when the pump outlet is at atmospheric pressure (760mhg), also known as the pumping rate.

The exhaust volume depends on the volume of the blade when it is out of contact with the intake port, that is, the volume of the basic element. Generally, when the volume of the basic element reaches the maximum value, it is separated from the intake port, so the exhaust volume can be calculated according to formula (2-13)

In fact, the liquid ring pump displacement and vacuum. For each design and production of a new structure of vacuum pump, the performance test must be carried out in the manufacturer, and the performance curve must be drawn to show the pumping capacity and power consumption under various vacuum degrees for the user to choose. Figure 2-12 shows the performance curves of szb-4 and szb-8 water ring vacuum pumps.

Limit vacuum and maximum discharge pressure

The limit vacuum degree refers to the vacuum degree when the discharge volume of liquid ring pump is zero. It can also be expressed by residual pressure (residual pressure = Atmospheric - vacuum degree), and the residual pressure is absolute pressure. Because the pressure in the container can not be reduced infinitely, when the inlet pressure is lower than a certain value, the liquid in the pump will gasify, or the leakage air volume at the high pressure side is equal to the suction air volume of the vacuum pump, or the volume coefficient is zero due to the high pressure ratio of the vacuum pump, which will make the vacuum pump unable to continue to inhale fresh gas, and the pressure in the container can not be reduced any more. When 15C water is used as sealing fluid, the residual pressure of single-stage pump can reach 30mmhg (about 4000Pa), and that of two-stage pump can reach 15mmhg (about 2000Pa); When used in series with jet pump, the residual pressure can reach 2 ~ 5mmhg (267 ~ 667Pa).

4、 Application examples of vacuum pump

Figure 2-13 shows the process of vacuum system commonly used in oil depot

(1) Make the centrifugal pump and suction line full of oil.

(2) Suction tank bottom oil.

(3) When the temperature is high in summer, the siphon can be caused by vacuum oil unloading.

The vacuum system consists of vacuum pump, vacuum energy, gas water separator and pipeline. Generally, water ring vacuum pump is used to get the required vacuum degree. In order to ensure the formation of water ring and circulating cooling in the vacuum pump, a gas-water separator is installed in series on the discharge pipeline of the vacuum pump. In order to ensure the smooth and reliable operation of the vacuum pump and prevent the oil from entering the vacuum pump, a vacuum tank is set on the suction pipeline of the vacuum pump. The purpose of vacuum staggered connection centrifugal pump is to clean the air in the pump and its suction pipeline and make them full of oil for pump filling. The purpose of connecting the vacuum tank with the crane pipe is to cause siphon phenomenon and suck the bottom oil. Flow and head of multi suction sewage pump