SCREW PUMP
In a screw pump, the fluid enters the outer suction manifold and passes through the meshing worm wheels to the central discharge manifold. The two worm wheels are driven by timing gears, to ensure correct clearance is maintained btw the screws. This clearance is responsible for the pumping action of the fluid.The most common arrangement is opposed helices (double suction) with the flow pattern being from the ends of the screw sets to the center of the pump.
For a single screw pump, there is no radial thrust but it gives an axial thrust because it discharges from one side to the other.
In a double/triple screw, the radial thrust is taken care by providing two screws being left handed and right handed. There is no axial thrust because it takes suction from both sides and discharges from the middle.
Double/triple screw pumps are provided with hardened and ground timing gear drive inorder to maintain a fixed axis of rotation thus avoiding metal to metal contact btw the screws and the casings.
Two screw pump hydraulic forces:
Hydraulic radial forces on a two screw pump rotor due to differential pressure are illustrated in Figure. The forces are uniform along the length of the pumping threads. These hydraulic forces cause a deflection ìd", for which running clearance must be provided in the surrounding pump body. Greater deflection requires larger clearances resulting in more slip flow or volumetric inefficiency, so ìd" must be kept to a minimum. Excessive deflection will cause damage to the surrounding body and/or contribute to rotating bend fatigue, which will ultimately result in shaft breakage.
In a screw pump, the fluid enters the outer suction manifold and passes through the meshing worm wheels to the central discharge manifold. The two worm wheels are driven by timing gears, to ensure correct clearance is maintained btw the screws. This clearance is responsible for the pumping action of the fluid.The most common arrangement is opposed helices (double suction) with the flow pattern being from the ends of the screw sets to the center of the pump.
For a single screw pump, there is no radial thrust but it gives an axial thrust because it discharges from one side to the other.
In a double/triple screw, the radial thrust is taken care by providing two screws being left handed and right handed. There is no axial thrust because it takes suction from both sides and discharges from the middle.
Double/triple screw pumps are provided with hardened and ground timing gear drive inorder to maintain a fixed axis of rotation thus avoiding metal to metal contact btw the screws and the casings.
Two screw pump hydraulic forces:
Hydraulic radial forces on a two screw pump rotor due to differential pressure are illustrated in Figure. The forces are uniform along the length of the pumping threads. These hydraulic forces cause a deflection ìd", for which running clearance must be provided in the surrounding pump body. Greater deflection requires larger clearances resulting in more slip flow or volumetric inefficiency, so ìd" must be kept to a minimum. Excessive deflection will cause damage to the surrounding body and/or contribute to rotating bend fatigue, which will ultimately result in shaft breakage.
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