Method and a device for automatic cleaning of trashracks at water intakes for water power plants and similar

The invention provides a device for automatic cleaning of trashracks. The device comprises a rake arm upheld by a support which is movable sideways in parallel with the trashrack. A wedge-shaped rake is pivotally mounted at the lower end of the rake arm, which by drive means is moved downwards and upwards along the trashrack, the rake thereby engaging the trashrack. During the downward movement the rake engages the trashrack only with its lower edge at which means are arranged striving to pivot the rake towards the trashrack. During the upward movement the rake is pressed against the trashrack with the whole end surface facing the trashrack.

BACKGROUND OF THE INVENTION 
The present invention refers to a device for automatic cleaning of 
trashracks at turbine intakes, fresh water intakes, waste water purifying 
plants and similar, at which a substantially wedge-shaped rake pivotally 
mounted at the end of a rake arm by driving means is moved together with 
the rake arm downwards and upwards along the trashrack, said rake arm 
transferring pulling and pushing forces from the driving means to the 
rake, the rake arm being mounted to a support, which is displaceable 
sideways in parallel with the trashrack. 
At trashracks trash of different kind, e.g. leaves, water plants and 
similar, is gathered at which a recurrent cleaning of the trashrack has to 
be made. In earlier days this cleaning was made manually by means of 
special rakes, which however was a heavy and physically trying work and 
besides almost impossible to perform at modern water power plants because 
of the high trashracks and great water depths occuring there. Therefore 
automatic raking equipments are nowadays used to a great extent. 
In the Swiss patent specification No. 396.779 such a device is described, 
where a carriage hanging in a lift rope is moved down and up along a 
trashrack by rolling on the bars of the trashrack. The carriage is 
provided with teeth extending in between the bars of the trashrack. A 
bucket is hingedly mounted to the carriage, which bucket during the upward 
movement of the carriage collects the trash which has been gathered at the 
trashrack and which during the downward movement is pivoted away from the 
trashrack. Such a device hanging in ropes is easily effected by side 
streams, which can occur at trashracks partly blocked up. Besides that no 
pushing force can be transferred to the carriage during its downward 
movement. Therefore it would be very difficult to penetrate e.g. an ice 
layer with this device. 
In the Swedish patent specification No. 302.430 is described a raking 
device comprising a rake member mounted at the end of a rake arm, which 
can be moved up and down along the trashrack and which is upheld by a 
support displaceable lengthwise of the trashrack. The rake makes by 
hydraulic means a cyclic movement, at which the rake arm is lowered to the 
bottom of the trashrack with the rake at a distance from the trashrack, 
the rake is then pressed against the trashrack and the rake arm is lifted, 
at which the rake broughts with the trash gathered at the trashrack and 
delivers it in a chute or similar above the trashrack. The support is 
moved sideways and the procedure is repeated until the whole trashrack has 
been cleaned. 
With this device a cleaning of the trashrack is performed only at the 
upward movement of the rake, at which all trash gathered in front of the 
trashrack is lifted by the rake and is delivered in e.g. a chute. 
Especially when the amount of trash is large a lot of power is required 
for lifting the rake and the device is exerted to considerable stress. A 
great deal of the trash gathered at the trashrack consists of small soft 
objects as leaves and plants, which do not cause any damage on e.g. 
turbines and therefore could be allowed to pass the trashrack. 
SUMMARY OF THE INVENTION 
On the basis of this fact and in order to reduce the power consumption of 
the raking device and the stress exerted thereto the wedge-shaped rake 
according to the present invention engages the trashrack both during its 
upward and its downward movement, at which the rake during its upward 
movement is pressed against the trashrack with its end surface facing the 
trashrack and during its downward movement engages the trashrack only with 
its lower end thereby making an acute angle with the trashrack. 
Thus during its downward movement the rake shoves away the trash gathered 
at the trashrack, whereupon a part of it can pass in between the bars of 
trashrack and a part is again gathered in front of the trashrack. This 
part of the trash which does not pass the trashrack is brought with the 
rake during its upward movement and is delivered in a chute or similar in 
the usual way. The amount of trash that has to be lifted by the raking 
device is considerably reduced. Owing to the fact that the rake during its 
downward movement engages the trashrack only with its lower end, the 
friction between the rake and the trashrack is reduced. The wedge-shaped 
rake can also penetrate e.g. an ice layer by means of the pushing force 
transferred by the rake arm. 
The invention also provides a device for performing the above described 
procedure, said device comprising a support arranged above the trashrack 
and being moveable sideways in parallel with the trashrack, said support 
upholding a rake arm at the lower end of which a rake is pivotally 
mounted, drive means being arranged to move the rake arm with the rake 
upwards and downwards along the trashrack, said rake being wedge-shaped 
with scraping edges at its upper and lower edges facing the trashrack, 
means being arranged striving to pivot the rake towards the trashrack with 
its lower edge.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The trashrack 1 is usually placed with an inclination in front of the water 
intake. When the trashrack 1 is blocked by trash the water level outside 
the trashrack rises, at which different water levels are obtained outside 
and inside the trashrack, which is shown in FIG. 1. In order to avoid 
troubles caused by this, e.g. risk for flooding and a decreased available 
power in the water power plant the trashrack 1 has to be cleaned. A track 
2 for a carriage 3 is arranged in parallel with the trashrack 1, said 
carriage 3 thereby being displaceable sideways along the trashrack. At the 
upper part of the carriage 3 a guide 4 is pivotally mounted, which by 
means of a hydraulic cylinder 5 can be brought into different inclinations 
relative to the carriage 3. The guide 4 has a double function, on one hand 
it serves as a support for a second hydraulic cylinder 6 arranged in 
parallel with the guide 4 and on the other hand it is arranged to guide a 
rake arm 9 which can be moved upwards and downwards. Pulleys 8 are 
arranged at the free end of the piston rod 7 of the cylinder 6. A further 
pulley (not shown) is arranged at the guide 4, said pulley together with 
the pulleys 8 forming a block means, which by means of a wire 10 exchanges 
the stroke of the piston. The wire 10 is with one end attached to the 
guide 4 at the attachment point 11 and with the other end at the lower end 
of the rake arm 9 at the attachment point 12. 
A rake 13 is attached at the lower end of the rake arm 9. The rake 13 is 
pivoted about the shaft 14. 
An embodiment of the rake is shown in FIG. 2. The rake 13 comprises a 
wedge-shaped frame structure, which at its upper edge facing the trashrack 
1 is provided with an upper scraping edge 15 and at its lower edge is 
provided with a number of scraping teeth 16, the distance between which 
correspond to the distance between the trashrack bars. Since the rake only 
comprises a frame structure, through which the water can pass, a lower 
water resistance is obtained. 
The rake 13 strives to pivot towards the trashrack 1 by means of a 
prestressing member. Said prestressing member can comprise a hydraulic 
cylinder 17, which is pivotally attached to the rake arm 9 close to its 
lower end and to the rake 13, as is shown in FIG. 3. By retracting the 
piston of the cylinder 17 the rake 13 is pivoted about the shaft 14 
towards the trashrack 1. In the embodiment according to FIG. 2 the shaft 
14 is spring-loaded, said spring constituting the prestressing member. It 
is also possible to stretch a wire of r similar between the rake 13 and 
the rake arm 9, said wire by means of spring force striving to pivot the 
rake 13 towards the trashrack 1. 
The raking device works in the following way. The device is started 
automatically by means of a level indicator, which is actuated by the 
level difference in front of and behind the trashrack 1. When the work 
cycle starts a pressure is obtained on the underside of the piston in the 
cylinder 5, at which the guide 4 together with the rake arm 9 is pivoted 
in clockwise direction according to FIG. 1 and the rake is brought a short 
distance away from the trashrack 1. However the spring-loaded shaft 14 (or 
the piston of the cylinder 17 e.g.) pivots the rake 13 towards the 
trashrack 1, so that the lower edge of the rake with the scraping teeth 16 
contacts the trashrack 1 and reaches in between the trashrack bars. 
At the same time as the cylinder 5 is actuated pressure medium is also 
delivered to the cylinder 6, which lowers the rake arm 9 with the rake 13 
to the lower edge of the trashrack 1. In FIG. 1 and with continuous lines 
in FIG. 4 the rake is shown during its downward movement. During this 
movement the rake 13 shoves away the trash that has been gathered in front 
of the trashrack 1, as is shown in FIG. 4. A part of the trash passes 
through the trashrack, another part is again gathered in front of the 
trashrack and a part may float up to the surface, from which it easily can 
be removed. 
When the rake 13 has reached its bottom position the guide 4 together with 
the rake arm 9 is by means of the piston of the cylinder 5 pivoted in 
counter-clockwise direction, so that the rake 13 is pressed against the 
trashrack 1. After that the rake arm 9 with the rake 13 is moved upwards 
by means of the piston of the cylinder 6, as is shown in FIG. 3 and with 
dash dotted lines in FIG. 4. During this upward movement the rake 13 
removes the trash which is still left in front of the trashrack 1. The 
scraping edge 15 is operating during this phase. The trash is delivered in 
a chute 18 behind the trashrack 1. When the rake 13 has delivered the 
trash the device is moved sideways along the track 2 a distance 
corresponding to the width of the rake and a new work cycle can start. 
The invention is of course not limited to the above described and in the 
drawings shown embodiments, but can be varied within the scope of the 
claims.