Selection Tips for Twin-Screw Pumps

No Chinese content provided, please provide the text to be translated.Screw PumpThe selection includes the choice of performance parameters and the selection of pump structural styles; for the selection of pump structural styles, please refer to the double.Screw PumpIntroduction to the structural form. 

Selection of Performance Parameters:1. Flow Q: As a volumetric pump, it affects the dual...Screw PumpThe main factors affecting flow rate are rotational speed.n, pressure p, and the viscosity v of the medium.

1.1 The Influence of Rotational Speed n:Screw PumpDuring operation, a sealed cavity forms between the two screws and their sleeves. With each revolution, one sealed cavity is moved from the inlet to the outlet, thus displacing an amount of liquid equal to the volume of the sealed cavity. Ideally, with no leakage within the pump, the flow rate of the pump is directly proportional to its rotational speed.Qth = n * q; where n represents the rotational speed, q denotes the theoretical displacement, i.e., the volume of liquid discharged by the pump per revolution, and Qth is the theoretical displacement.
1.2 The Impact of Pressure △P:Screw PumpDuring actual operation, there is an internal leakage, also known as slip. Due to the presence of a certain gap in the pump's sealing chamber, as well as a pressure difference before and after the chamber.△P, therefore, a portion of the liquid recirculates, indicating a leak. The leakage amount is represented by △Q, so Q = Qth - △Q. It is evident that as the pressure difference △P between the front and rear of the sealed cavity increases, the leakage amount △Q gradually increases. The impact varies for different line types and structures.
1.3 Impact of Viscosity 'v': Imagine: The same volume of clear water and thick paste is poured out from a funnel-shaped container. Clearly, water leaks out faster than the paste. Similarly, for double...Screw PumpHigh-viscosity fluids tend to leak less than low-viscosity liquids, with a proportional relationship between the leakage amount and the medium's viscosity. In summary, a comprehensive consideration of the aforementioned factors is required, followed by a series of calculations to accurately determine if the pump's actual flow rate meets the operational requirements. 
2. Pressure △P: Unlike centrifugal pumps, dual...Screw PumpNo Chinese content provided. Please provide the text to be translated.△P is determined by the discharge load, that is, by the discharge resistance. The discharge resistance matches the pressure at the pump's discharge port, with higher discharge resistance resulting in greater working pressure. To determine the pressure, knowledge of fluid mechanics is required for the discharge resistance.PreciseThe calculation.
3. Axial Power N: The shaft power of the pump is divided into two parts: Nth - hydraulic power, which is the energy of the pressure fluid; Nr - friction power. For a given pressure and flow rate, the hydraulic power is constant, so the factor affecting the shaft power is the friction rate, Nr. Friction power is the portion of power consumed due to friction in moving parts. It is evident that these friction powers increase with the increase in working pressure difference, and an increase in medium viscosity also leads to an increase in fluid friction power. Therefore, in addition to hydraulic power, the pump's shaft power includes friction power that increases with both medium viscosity and working pressure. Consequently, when selecting a matching motor, the viscosity of the medium is also a very important reference data. Particularly when transporting high-viscosity media, it is necessary to conduct comparisons.CorrectAfter calculating the power, when selecting the matching motor, follow the relevant regulations specified in the sample table. N(KW): N≤10, 10＜N≤50, N＞50, N＞100. K: 1.5, 1.25, 1.15, 1.1. Nm = N.K, Nm----motor power, N----axial power, K----power reserve coefficient.

4. Calculation and Selection of Suction Performance: The operation of a pump is divided into the following stages:
4.1 Inhale, as the liquid continuously moves along the intake pipe.
4.2 The rotating screw transfers energy to the working fluid;
On 4.3 extrusion, the liquid is discharged from the pump at a pressure necessary to overcome all resistances in the extrusion pipeline system. Among the three stages mentioned, the critical stage is to ensure the suction conditions of the pump, which is essential for the pump to operate normally. Failure to do so can lead to cavitation, causing vibration and noise issues.
5. Calculation of NPSH (Net Positive Suction Head) Allowance: The NPSH required by the pump, NPSHr, is related to various factors such as the pump's speed, n, the head, h, and the viscosity, v, of the medium being pumped. For the Bornemann double-suction pump introduced by our factory...Screw PumpPlease calculate using the following formula:NPSHr = (1.5 + 0.253VF * 1.84345 + 0.0572VF * 1.55) * v^0.4146 * VF; VF = n*h/60 (m/s); n = speed (r/min); h = pitch (m); v = working viscosity (°E). This indicates that the pump's NPSHr increases with the increase of VF and v. Therefore, in cases of poor suction conditions, it is advisable to select a pump with a smaller pitch.Screw PumpThis is crucial during the selection process. 
5.1 Calculation of the NPSHa for equipment cavitation margin; this will not be elaborated upon here.
5.2 To ensure the pump operates normally without issues such as cavitation and vibration, the following conditions must be met: NPSHa > NPSHr. This is the pump's suction condition. 6. DoubleScrew PumpThe selection of rotation speeds: Selecting different rotational speeds often involves the following issues:6.1 By selecting the appropriate pump speed, achieve appropriate performance parameters such as flow rate. 6.2 The pump speed should also be adjusted according to the viscosity. For the Boremann double...Screw PumpThe change in viscosity is the main factor determining the rotational speed; as viscosity increases, the allowable rotational speed decreases. The selection of the rotation speed essentially addresses the issue of suction performance, particularly under high viscosity conditions. If the rotation speed is chosen too high, it can lead to insufficient suction, thereby causing noise and vibration issues. Therefore, it is imperative to adhere to the relevant principles when selecting the rotation speed.