Page 297 - Centrifugal Pumps 2E

Hydraulic Power Recovery Turbines 267

tilting the guide vanes (Part #1) about a pivot pin (Part #4) parallel to the
runner (Part #6) shaft axis to vary the velocity of the liquid flowing
through the assembly at a proper flow orientation angle relative to the
runner. Each guide vane is held in position by the pivot pin and by a slide
pin (Part #5), which moves the guide vane by its position in the slot
through the vane.
The pivot pins are located in the two stationary vane rings or stage
pieces (Part #2) and the slide pins are assembled to the two rotatable vane
rings (Part #3). The stationary and rotatable rings establish the width of
the inlet opening. They are the side walls of the vane assembly. The oper-
ating position of the vanes and the resultant through-flow cross-section
area is dependent on the angular position of the rotatable vane ring in
relation to the stationary rings.
Between the guide vanes, the rotatable vane rings are shaped in a man-
ner to achieve the correct velocity increase for each through-flow cross-
section area.
The rotatable vane rings perform the additional function of avoiding
undesirable vane flutter, by a clamping action due to developed differen-
tial pressure. A reduction in pressure occurs in the flow passages due to
the increase in velocity of the fluid, while the pressure acting on the out™
ward side areas of the rotatable rings is essentially the same as at the en~
trance to the vane passages.
Because of the relatively large outward side areas of the rotatable
rings, the clamping force is higher than the different hydraulic forces that
act on the guide vanes and could cause vane flutter. However, the force is
not restricting the adjustment of the guide vane position during operation.
The cross-section of this HPRT is shown in Figure 14-16. The turbine
is built basically like a multi-stage pump with standard bearing housings.
The runner eyes of each stage face all in the same direction and a drum
takes care of balancing the axial thrust.
Figure 14-17 shows the crossunder in the bottom half. There are no
crossovers. The top half contains the yoke assembly, which moves up and
down and creates the rotational position of the rotatable rings and subse-
quently the resultant through-flow cross-section area of the guide vane
openings.
A crossbeam as shown in Figure 14-18 connects the yokes for synchro-
nous travel. Individual setting of through-flow areas for each stage is
possible by adjusting the nuts on the crossbeam. If required, through-
flow areas for each stage can be adjusted differently to allow for an in-
crease in the specific volume for compressible liquids, when the pressure
reduces from stage to stage. This is another feature to achieve optimum
performance. The up-and-down movement of the beam can be achieved
by an electric or pneumatic actuator that is mounted on top of the beam
cover,