TWIN SCREW PUMP

First of all, the speed of the pump should be determined according to the viscosity of the medium being conveyed. At different working temperatures, the viscosity of the medium is different, and it is necessary to determine the maximum medium viscosity that may occur at the current working temperature. If the actual viscosity is higher than the estimated viscosity, there may be insufficient power.

According to the viscosity of the medium at the working temperature, the rotation speed n of the pump is determined: generally, when V≤1000mm2/s, n=1450r/min is allowed; when V≤3000mm2/s, n=750~950r/min is allowed. When V>3000mm2/s, n=600~750r/min is allowed.

Please carefully consider the NPSH value of the pump and the NPSH value of the pipeline; the higher the viscosity, the more attention should be paid. Generally speaking, when the viscosity exceeds 1000mm2/s, the inlet resistance of the pipeline should be calculated before selection. If the inlet resistance does not meet the requirements, it will cause damage to the pump. Therefore, remind the user to calculate or submit it to the technical department of our company for calculation.

When high-viscosity materials are transported in the pipeline, it should be noted that if the pipeline resistance is too large, the load will increase sharply, and the conventional shaft power calculation will cause the problem of insufficient power. When handing over to our company for calculation, the user should provide the corresponding inlet pipeline information, including the pipeline length, height difference, filter elbow tee and other accessories, and our company’s technical department will provide the selection.

In order to facilitate users to configure pipelines, the R&D department of our company has developed pipeline selection software, which saves a lot of calculation time and provides convenience for users.

The model of the pump can be determined according to the flow rate, the pressure difference between the inlet and the outlet, the viscosity of the medium and the speed of the pump.

How to determine the model of the pump is further explained as follows:

2.1 According to the flow rate and pressure, determine whether to choose a double-suction product or a single-suction product.

Note that as long as the conditions are met, try to use single-suction products, because single-suction products have a simple structure and are easy to load and unload.

Generally speaking, when the flow rate is not large and the pressure is not high, the single-suction product (ie BY2G type or BY2GX type) is used; on the contrary, when the flow rate is large or the pressure is high, the double-suction product (ie the BY2GS…series) is used. . The single-suction product has a simple structure and is easy to maintain. It is preferred to use it as far as possible.

2.2 Determination of sealing form.

What kind of sealing form is adopted depends in many cases on the needs of the working conditions or the user’s preference. However, it should be noted that the use of packing seals will produce more or less trace leakage. Leakage that meets the requirements of industry standards and national standards is allowed, but when transporting toxic and harmful liquids, it is forbidden to use packing seals. such substances, double mechanical seals should be used to achieve long-term zero leakage. For the transportation of high-viscosity chemical materials, if there is no suitable sealing liquid, the packing seal should be used to realize it. Otherwise, the mechanical seal may be scrapped in a very short period of time due to the inability to obtain timely cooling, or be affected by high-viscosity material’s effect and fail.

2.3 The heat preservation method and installation method are the relevant structures of the pump selected by the user according to the conveying needs of the medium. When the user does not make a request, our company will produce according to the content of the default item.

2.4 Bypass valve, which plays the role of overload protection in the pump unit. It is configured according to the user’s needs. Our company will not configure the bypass valve if the user does not ask for it. We recommend using other methods to protect the pump unit from overload, such as: automatic shutdown of the motor when the motor is overloaded, pressure relays in the pump discharge pipeline system and installation of solenoid valves, etc., which are simpler, more reliable and more sensitive.

The motor is the most commonly used driver for the pump unit. After selecting the pump specification, find out the shaft power N corresponding to the flow rate of the pump of this specification under the working pressure P from the table according to the corresponding viscosity V. With the shaft power, the motor power can be determined.

The optional motor power Nm should be slightly larger than the found shaft power N. When the power is relatively small and the pressure is relatively low, the reserve should be larger. The applied power reserve is Nm≥K·N, and the K value is shown in the table below. With the motor power, the model and specifications of the motor (or geared motor) are determined according to the explosion-proof requirements and other conditions required by the user. After the user selects the pump, please ask us for the unit size of the pump and motor required for the foundation construction design.