Application of Fluid Couplings in Drives with a Vertical Axis of Rotation
Abstract Generated abstract
This paper examines the use of hydrodynamic fluid couplings in drives with a vertical axis of rotation, focusing on how their torque transmission characteristics differ from those of horizontally mounted couplings. It analyzes the effects of wheel arrangement, filling level, slip, interwheel gap, and meridional section depth, showing that vertical-axis couplings can transmit lower torque at small slips and may exhibit ambiguous characteristics under partial filling. The study concludes with design recommendations: full couplings should preferably place the turbine wheel below or use increased section depth, while partially filled couplings should preferably place the pump wheel below and may require devices to stabilize flow and enable starting at low fillings.
Full Text
Application of Fluid Couplings in Drives with a Vertical Axis of Rotation
Yu. I. Kapustin
An analysis of the principal approaches to increasing the service life of machines associated with the transmission of mechanical energy shows that the common measure for increasing their durability is the reduction of harmful dynamic loads. To solve this problem, hydrodynamic couplings have found wide application. Their property of limiting and not transmitting torsional vibrations through themselves creates, in all cases, favorable conditions for gear transmissions.
Fig. 1. External characteristics of fluid couplings: 1 — with a horizontal position of the axis; 2 — with a vertical position of the axis and the pump wheel located below; and 3 — with the pump wheel located above.
When using fluid couplings in drives with a vertical axis of rotation, it is necessary to take into account the distinctive features of the characteristics of the latter in comparison with analogous characteristics of fluid couplings with a horizontal axis of rotation. A study of the characteristic features of these fluid couplings has shown that completely filled fluid couplings with a meridional-section profile of the “Vulcan” type transmit, at small slips, a somewhat smaller torque than with a horizontal axis. At the same time, this torque is not the same for fluid couplings,
having different relative positions of the runner wheels. Such characteristics are shown in Fig. 1.
Fluid couplings with a vertical axis of rotation become sensitive to the magnitude of the gap between the wheels. In this case, as it increases, the torque decreases, especially markedly in fluid couplings with the lower position of the pump wheel (Fig. 2). Increasing the depth of the meridional-section form of the turbine wheel, with the axis vertical, substantially increases the torque transmitted by the fluid coupling, whereas increasing the section depth of the pump wheel does not lead to a noticeable increase in it.
Fig. 2
The characteristics of a fluid coupling at partial fillings also have certain special features, especially with the lower position of the turbine wheel (Fig. 3). As can be seen from the figure, the external characteristics at large fillings \((q > 50\%)\), at slips greater than critical, are ambiguous. Characteristic 1, obtained during braking, does not coincide with characteristic 2, obtained during release of braking. At medium fillings \((35\% \le q \le 50\%)\), ambiguity is retained only in the dynamic characteristics, i.e., characteristics obtained over a short interval of time. The static characteristics during braking and release of braking coincide.
One of the essential features of these coupling designs is that at fillings below the critical value (in the experiments this filling was 35%), during start-up they are unable to transmit torque. In order for the fluid coupling to begin transmitting torque, it is necessary, by some means, to force the pump wheel to entrain the liquid located in the turbine wheel. Only then is a circulation flow established and the fluid coupling begins to transmit torque. After the circulation flow has been established, it is not disrupted even when the turbine wheel is stopped.
A feature of the characteristics of fluid couplings with the lower position of the pump wheel is the significantly smaller value of the critical slips in comparison with analogous characteristics of fluid couplings with a horizontal axis.
Thus, when using fluid couplings in drives with vertical axes, the following should be taken into account:
- Couplings operating with full filling should preferably be arranged so that the turbine wheel is located below. If such an arrangement is impossible, then, in order to eliminate the influence of the position of the axis of rotation on the torque transmitted by the coupling, the depth of the meridional section of both wheels must be increased and made equal to 1.20 times the section depth of fluid couplings with a horizontal axis. In some cases it is possible to confine oneself to increasing the section depth only of the turbine wheel.
Fig. 3.
- In drives with partially filled fluid couplings, it is preferable to arrange the coupling design so that the pump wheel is located below. In the case of a lower position of the turbine wheel, in order to eliminate ambiguity of the characteristics at slips greater than the critical values, it is necessary to provide special devices, such as thresholds, diaphragms, etc. In fluid couplings operating at low fillings, moreover, it is necessary to provide special devices which, during the starting period, serve to lift the liquid from the cavity of the turbine wheel into the cavity of the pump wheel.