This however leads to a relatively long pump to facilitate vertical isolation. As the pump is withdrawn vertically for major overhaul work, a suction isolating valve is not required. Maintenance of the bowl pump is also difficult and the crane normally has to be sized to take the total pump weight for installation and overhaul. On the debit side, the bowl pump arrangement has a much higher mechanical pumping equipment cost. There is no complicated volute to construct, and as the pump has a smaller overall diameter than the concrete volute, the pumphouse floor area is smaller. With this design, the pump forms part of the piping and its intake is from a relatively unsophisticated suction chamber it generally has a smaller civil engineering cost than the equivalent concrete volute design. On low head coastal applications, standard gear-driven units have been installed, while on the higher head inland cooling tower applications, it has been possible to use a direct motor drive while still retaining the same equivalent specific speed as the equivalent gear-driven units.Īlternative bowl pump designs have been used extensively on overseas applications. Volute casing designs have been used by the CEGB for pumping duties up to around 8 m 3/s. On either side of the bep capacity, the radial load increases and can be substantial at low capacities.Ĭondensers, pumps and cooling water plantīritish Electricity International, in Turbines, Generators and Associated Plant (Third Edition), 1991 12.3 Vertical pumps 12.3.1 Vertical metal-casing pumps The volute casing has a uniform casing pressure characteristic at the bep (best efficiency point) with close to zero radial load. The tangential volute can be expected to have an extra point of efficiency or two over an ideally designed centerline discharge due to the absence of the extra, constricted, 90° turn. The piping load on the tangential volute casing results in a downward force on the nearest leg and bolt to the discharge and a upward force on the farthest. Its vertical centre line orientation splits the piping load evenly over the two pump casing feet and hold down bolts. The centre line volute has come into common use in the process industries where piping and process changes are common and the pump is used to support piping loads. and then has a discharge axis that is radial to the impeller axis on its vertical centre line. The centre line volute wraps around the impeller o.d. The tangential volute has a discharge centre line that is parallel to a tangent at the impeller o.d. The volute casing has a cross-sectional collecting area that continually increases from the cutwater (or tongue) to the conical diffuser leading to the exit flange. This chapter ends with the effects of volute and rotor width on characteristics of squirrel-cage fans. Unlike the traditional nondimensional parameters that take no contribution from volute dimensions, new parameters are introduced that consider both rotor and volute dimensions in the fan design process. The subsequent sections focus on new definitions for nondimensional parameters and a joint volute–rotor approach for design of squirrel-cage fans. Twin outlet volutes are also introduced as a casing that can be used when the fan must supply air to two separate zones. A study on slip factor inside the fan is then given. The general form of the frequency spectrum of the velocity in the volute and the effect of stall on it are analysed. The velocity distribution at the rotor outlet and the flow patterns inside the volute are examined. This chapter deals with the volute of forward-curved centrifugal fans and the effects of its modification on fan performance. Moastafa Mahmoodi, in Developments in Turbomachinery Flow, 2015 Abstract
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