Automatic grab crane

A time saving automatic hydraulic control for that sequence in operations in which a grab excursioning out of sight of the operator, is sequentially lowered open to engage work material, closed to pick up a load, and then hoisted with its load and emptied. A logic circuit is activated to stop the lowering within an adjustable timed period after initial work engagement to provide desired penetration of the work material by the grab followed by a minimal time for grab closing to provide an adjustable constancy of loads and a positive sequential control for the lowering and hoisting modes.

BACKGROUND OF INVENTION 
By way of example of all grab cranes, the operation of a dredge crane 
operating a grab having plural sides, such as a two sided clamshell bucket 
in underwater dredging, may be considered. Such involves the sequential 
steps of lowering, closing, raising, luffing out, opening, luffing in, and 
again lowering, etc. under changing bottom depths and flowing water. The 
three steps of lowering, closing and raising are the three along with 
braking that are the most critical, and are the most difficult to program 
either manually, or otherwise, because they occur out of sight of the 
crane operator. Even if visible through clear water over a range of depths 
it would be difficult to determine visually when the bucket has 
established a desirable working position with respect to the bottom and is 
ready for closing to pick up a load in a single pass without either 
"burying" the bucket or "skimping" the load. Objectionably, slack hoist 
lines from poor braking can permit the "burying" of a bucket and incur 
many kinds of delaying complications including the tilting or tumbling of 
the bucket, improper closing of the bucket, and, undue stress movements on 
the hoist. 
Full automation for a wide range of changing depths and conditions is 
highly desirable for these three steps. However, confusing conditions are 
experienced because in the above sequence two non-contiguous steps occur 
when the bucket is the lightest on its hoist winch, namely, when the winch 
brake is applied for luffing and opening the bucket, and when the bucket 
engages the bottom and is closed. Also two non-contiguous steps occur when 
the bucket is the heaviest on the winch, namely, when being raised and 
when being lowered. In both, similarities between the alternative steps 
provide like conditions that are substantially indistinguishable for 
automated monitoring, and, any requirements or provisions for manual 
override for these steps involves delays and further complications that 
permits only partial automation. Additionally, two power efforts are 
involved and their coordination and control have to be transmitted to the 
bucket through separate connections additionally carried by the boom. One 
effort is to open and close the bucket, and the other effort is to raise 
and lower the bucket. Heretofore, these efforts have generally been 
controlled separately and manually with a substantial waste of operational 
time and power. Accordingly, time and labor saving operative automation 
has heretofore been limited. 
SUMMARY OF INVENTION 
The words "dredge bucket" or "dredge crane" as hereinafter used may be 
construed to include all grab cranes in which the development and 
experimentation indicates preference for hydraulic power in raising, 
lowering, and closing a clamshell bucket, such as used in dredging, and it 
is with the coordinated operation of these three functions that the 
invention is primarily concerned particularly while the grab is under 
water or otherwise out of sight in handling wet or dry material. 
Accordingly, the hoist line winch is powered hydraulically; time 
responsive relays and solenoid valves are used sequentially as controlled 
by pressure to particularly distinguish between the steps of lowering, 
bottoming, digging, and raising the clamshell bucket; and, these steps are 
performed sequentially and temporally as coordinated by electrical 
circuitry in an economical and efficient hydraulic driven dredge 
arrangement with uniform results and savings in dredge time. 
Further objects of the invention include the provision of grab cranes 
simplified in structure and control and less complicated to maintain and 
operate. Hydraulic responses are instantly effective because of an assured 
incompressibility of the liquid involved. Fewer elements are involved, 
and, with the vulnerable and adjustable working parts accessibly disposed 
for ready servicing they are protected above the deck of the dredge where 
they are substantially free from abrasion by the materials handled. 
Moreover, the elements can operate in an automatic sequential mode 
continuously subject to immediate manual take over control when required, 
or, fail safe at any instant. The bottom sensing circuit can also be 
adjustably programmed to dig to an operational depth with the hoisting, 
luffing, and lowering of the bucket at operational speeds that can be 
adjusted to suit particular work conditions and material handled.

DESCRIPTION OF INVENTION 
Referring now to the drawings and FIGS. 1 and 2 in further structural 
detail, a floating dredge 10 is illustrated having an arched shear 12 or 
"boom" having two legs 13 pivotally mounted at their heels 14 on the deck 
11 for movement from its upright position as shown in full lines 15 for 
hoisting and lowering the clamshell bucket 16 through the digging well 18, 
to an inclined position shown in broken lines 19 for luffing and opening 
the bucket to empty its load in the hopper 20. The shear 12 is moved 
hydraulically between its alternate positions by means of extendible guys 
23 that include auxiliary powered hydraulic luffing cylinders 21. 
The clamshell bucket 16, sometimes referred to as a grab bucket, has two 
semi-circular jaws 22 pivoted to an axle 31 disposed at their radial 
centers 24, and have toothed lower digging edges 25. At their upper edges 
26, or along their upper edges, if underslung, they are pivoted to the 
lower ends of spreader strut links 27. The upper ends of the links 27 are 
pivoted on a common axis to a head 28 to which dual hoist lines 30 are 
attached. Bucket actuating hydraulic cylinders 32 interconnect the axle 31 
and head 28 and close the bucket jaws 22 for digging by contraction under 
hydraulic pressure supplied through the hose 33 by a separate pump HP 
(FIG. 1) controlled by a solenoid valve BV (FIG. 4). After hoisting the 
closed bucket 16 for emptying, the relaxation of the hydraulic pressure 
permits the jaws 22 to open downwardly under their own weight to dump a 
load. A hose reel 36 carried on a platform 40 at the top of the shear 12 
supports the hydraulic hose 33 to pay out and retrieve the hose without 
slack as the bucket is lowered and raised. 
The hoist lines 30 are laid over the head sheaves 42 and guide sheaves 43 
on the shear 12 and are wrapped and secured around a hoist winch 44 
mounted on the deck 11. The power for the hoist winch hydraulic motor M to 
raise and lower the bucket is provided preferably by a continuously 
running positive and variable displacement reversible flow hydraulic pump 
means P driven by a prime mover PM which may be an electric induction 
motor as shown when shore power is available, or a speed regulated diesel 
engine operating at a constant regulated speed. 
In the present invention certain pressures may be assumed for explanation 
purposes in automating a clamshell dredge utilizing hydraulic pressures 
with controls that distinguish between lowering, bottoming, digging and 
raising the clamshell bucket in an economical and efficient hydraulic 
hoist circuit C. The hydraulic circuit C includes the pump P; a flow 
reversing means FR; the hydraulic motor M; a pressure conduit PC; a return 
conduit RC; a bypass conduit BC connected between conduits PC and RC; a 
hydraulic supply cooling reservoir R receiving leakage of pump P, motor M, 
and brake hydraulic pressure release through conduits D; and, a pump RP 
replenishing the circuit C under pressure. Thus, a liquid solid condition 
is maintained in the circuit C by the constant low supply pressure of pump 
PR, such as 400 p.s.i. that is effective in both the pressure conduit PC 
and the return conduit RC. This pressure along with pressure induced by 
the free weight of the open bucket 16 on the winch motor M when being 
lowered, may develop a hydraulic pressure of 1,200 p.s.i. in the conduit 
PC. After the bucket enters the water the pressure in conduit PC may drop 
to 900 p.s.i. due to the effective weight of the bucket being reduced by 
its buoyancy factor and the inertia of the water resisting its downward 
movement. The 900 p.s.i. pressure endures without reducing the speed of 
downward movement of the bucket until the bucket touches bottom to which 
further consideration is given later. The load lift pressure will be well 
above 2,000 p.s.i. until the bucket emerges from the water whereupon the 
maximum lift weight will be experienced when load buoyancy ceases. 
As again referred to later, when lowering the bucket 16, the hydraulic flow 
direction is reversed by the flow reversing means FR and the pressure of 
1,200 p.s.i. at the intake of the pump P is developed by the weight of the 
bucket 16 driving the pump P. In this mode, the load powers the winch, the 
winch drives its positive displacement motor M and it acts like a "pump" 
while the positive displacement pump P rotating at its controlled speed 
becomes a metering device controlling the lowering speed of the bucket 
through pressure flow in conduit PC. 
The flow reversing means FR may comprise either a flow-direction reversing 
valve or a reversing variable displacement pump. Both have a normally 
neutral position (FIG. 5) blocking flow into the conduits PC and RC and 
alternate positions by which the flow-direction in the circuit C, for 
hoisting, would be in the direction of arrows H, and when reversed for 
lowering the flow would be in the direction of arrows L. A reversed flow 
mode is shown in FIG. 5. Either means that may be used operates valves 
with a timed progressive closing and opening action and is controlled by a 
reversing lever RL controlled by a dual reversing solenoid RS normally 
having a center-off position for neutral N position and controlling the 
reversing valve for either fast or slow movement. 
In this condition the flow reversing valve FR construction is 
diagrammatically shown in FIG. 5 where a cylinder having axially and 
equally spaced opposing pairs of ports M.sub.1 and M.sub.2 for motor 
connections and P.sub.1 and P.sub.2 for the pump connections. A piston VP, 
having a movement dampening bleed passage BP axially through it, has on 
opposite sides two surface channel grooves G.sub.1 and G.sub.2 extending 
200.degree. and spaced to coact in one position with the axially spaced 
pump ports P1 and P2 indicating forward and return flow. On the same side 
of each channel groove there are provided spiral grooves SG.sub.1 and 
SG.sub.2, as indicated, also extending 200.degree. with their ends spaced 
the same distance as the spaced ports but with the ports displaced from 
the planes of grooves G.sub.1 and G.sub.2 a distance whereby the piston 
closes the pump ports P1 and P2 in the neutral position N of the reversing 
valve. Grooves G.sub.1 and SG.sub.1 may intersect because neither is 
connected to a port when the other is. 
A further axial groove G.sub.3 on the pump port side of the piston has its 
ends preferably out of communication with the other grooves but opening 
between them to place the pump ports P1 and P2 in communication with each 
other when the valve piston VP is in neutral position N and also blocks 
any flow through ports G.sub.1 and G.sub.2. Thus, with the deceleration of 
the winch at the top of the hoist by the rheostat RR, as later described, 
brake B can be applied just as the flow through the bypass groove G.sub.3 
finally conducts the complete hydraulic pump output through port M.sub.1. 
This reversing means is relied upon for positively and selectively 
determining the raising or lowering mode of the winch motor M that is 
rotatively coupled with the hoist winch 44. In its neutral center-off 
position N there comparatively is no longer a higher pressure in the 
conduit PC except when the winch supports a load without the application 
of the winch brake. 
Thereby, in position H to hoist the bucket 16, the prime mover PM powers 
the pump P through the reversing control FR to drive the hydraulic motor M 
for hoisting the bucket and this places one of the higher pressures (2,000 
p.s.i.) in the conduit portion PC. In position L to lower the bucket the 
flow-direction reversing means FR reverses the flow-direction in conduits 
PC and RC, the weight of the bucket 16 reversely rotates the motor M and 
drives the hydraulic fluid in the reverse direction as indicated by arrows 
L, and, this places the other higher pressure (1,200 p.s.i.) also in the 
conduit portion PC. 
Accordingly, in both instances, the higher hydraulic pressures when present 
are always confined to the one leg PC of the conduit C as well as the 
pressure 900 p.s.i. which occurs when the bucket enters the water. In the 
neutral position N the reversing control re-circulates hydraulic fluid in 
the pump while the circulation of hydraulic fluid in the conduit C is 
blocked thereby locking the winch motor M against rotation. This condition 
supports the bucket at a fixed height with resulting higher pressure in 
the conduit PC holding the winch motor M against rotating. Any higher 
pressure can be relieved by applying the winch brake B. 
The bypass conduit BC interconnects the two conduits PC and RC in an 
orientation that is parallel to the pump P and to the motor M and it 
includes a vent valve VV operated by a solenoid VS as a forward flow valve 
that is protected against counter pressure and backflow by a backflow 
check valve CV. The valve VV maintains the higher pressure in the pressure 
conduit PC whenever the winch and motor are to be rotated. But when the 
winch is to be stationary without movement of the flow reversing valve FR 
to its neutral position N the vent valve VV preferably a spool valve may 
be opened by solenoid VS to vent the high pressure in conduit PC to the 
return conduit RC for a pressure equalization as when the bucket is on the 
bottom. This enables the speed governed pump P to continue operation and 
re-circulate without load or working pressure thereon. Thus, the valve VV 
may be opened and closed by the digging relay switch DR. 
The brake is controlled by the applicator BA which has a spring S to apply 
the brake B and a pressurizable cylinder CY which receives hydraulic fluid 
to overcome the spring S and release the brake B. A standing source of 
pressure is provided by the tank PT having an inert gas in it compressed 
by hydraulic fluid supplied from conduit PC as accumulated and trapped by 
the check valve TV at the maximum pressure exerted in conduit PC when the 
bucket with its load is being hoisted. When the electromagnet EM is 
de-energized by the opening of the pressure switch PS at low pressure the 
spool spring SS will urge the valve SV to its normal position shown in 
FIG. 4 venting the pressure cylinder CY to the reservoir R through the 
drain D. Thereupon, the spring S will apply the brake B and incidentally 
provide electrically and hydraulically a fail safe arrangement regardless 
of bucket position. Then, the energization of the electromagnet EM moves 
the spool valve SV to its alternate position applying pressure from the 
tank PT to the cylinder CY thereby releasing the brake B. The 
de-energization of the electromagnet EM is also accomplished by the 
opening of limit switch LSL1 as later explained to apply the brake at the 
luffing position of the bucket. 
Coacting with and cooperating in the operation of the arrangement described 
is a worm drive WD rotated by the winch. It axially displaces two cam 
followers C1 and C2 to actuate the cam switches LCS and UCS alternately, 
and sequential switches LSL 1 and 2. Cam switch LCS2 is closed to power 
the underwater controls just after the bucket 16 enters the water where 
the pressure drops to said 900 p.s.i. Switch LCS1 is closed for out of 
water operations and when the upper cam switch UCS is actuated as the 
bucket nears the upper hoist limit the luffing control is made ready. 
Sequential switches LSL 1 and 2 terminally slow down and stop the hoisting 
for application of the brake B during the luffing and opening of the 
bucket. 
By way of illustrating the sequence of steps performed, the cycle of the 
grab operation is indicated in FIG. 7 in which arrows indicate the grab 
movement and the sequence desired. The grab, when emptied, is open and is 
luffed out to its lowering position, the brake B is released, and the grab 
is lowered. When submerged, the effective weight of the grab is decreased 
on the hydraulic system. This decrease in effective weight is followed by 
activation of the bottom sensor means PR1 and PR2 by the winch W closing 
the cam switch LCS2. The sensor means responds immediately to any 
hydraulic pressure change occasioned by the bucket touching the bottom and 
this triggers the timing means LR and TR which provides a predetermined 
fraction of a second delay that permits limited penetration of the work 
material and applies the brake B to provide a predetermined looseness in 
the hoist line 30. The bucket is then closed to dig the work material to a 
depth permitted by the hoist line looseness after which the brake B is 
released and hoisting begins followed by deactivation of the bottom 
sensor. When the bucket is raised to its open position the brake is again 
applied and the loaded bucket is luffed to its dumping position. There the 
bucket is opened to discharge its load and is ready for a repeat of the 
cycle. 
More particularly in detail, assuming a starting point, the lowering 
solenoid L is energized by closing the lowering switch LS manually or 
automatically. Switch LS also energizes relay LSR to close its 
self-holding switch LSR2 through normally closed switch DR2, connection 61 
and 62 to provide the bucket lowering mode in which switch LSR1 is closed 
and switch LSR3 is open. Then the worm drive WD closes the cam switch 
LCS2. 
Assuming as a starting point that the lowering solenoid L is energized 
through normally closed switch DR2, connection 61, switch LSR2 and 
connection 62 to provide the bucket lowering mode, then the closing of the 
cam switch LCS2 right after the bucket enters the water readies two 
pressure responsive solenoids PR1 and PR2 to close switches responsive to 
the pressure in conduit PC as adjusted with respect to the 900 p.s.i. This 
readiness is established automatically with the weight of the lowering 
grab on the winch overrunning the prime mover PM and developing a rather 
constant pressure in conduit PC when the bucket engages bottom the 
pressure in conduit PC is pulsed momentarily either positively or 
negatively, or both, and actuates one or both of the pressure relays, PR1 
and PR2. Relay PR1 will monitor an increase in pressure while relay PR2 
will monitor a drop in pressure. The response will establish a spike-like 
pulse of very short duration but one that is long enough to trip a 
latching relay LR to record the pulse long enough to utilize it to actuate 
a timer relay TR that is adjustable for closing within a range of a 
second, e.g. approximately 0.3 of a second. This adjustable recording 
provides both a desired earth penetration by the bucket and a desired 
slight overrun of the winch 44 for it to pilot the digging depth limit of 
the bucket. 
When the timer delay relay TR closes five further operations occur, namely: 
1. the digging relay DR closes switch 1 to ready underwater operations and 
de-energizes above water operative circuits by opening switch 2 and 
de-energizes the self-holding lowering solenoid relay LSR to open switch 
LSR 2 and de-energize switch LSR3; 
2. a pressure vent valve solenoid VS is de-energized or energized either by 
opening or closing switch DR1 or opening switch DR2, respectively, to 
equalize pressures between conduit portions PC and RC depending upon to 
which switch connection 61A is made. The vent period is the same; 
3. the resulting pressure drop in conduit PC registered by solenoid PS 
opens its switch and de-energizes the electromagnet EM to permit the 
spring SS to move the spool valve SV to vent the hydraulic pressure in the 
brake applicator BA whereupon the spring S thereof applies the brake B to 
the winch 44; 
4. the closing of the switch DR1 activates the bucket control BV and times 
a hydraulic pump HP through the connection 58 to pressurize the bucket 
hose 33 and thereby powers bucket cylinder 32 to close the bucket; and, 
5. the opening of switch DR2 opens the supporting circuit 61, later 
described, and de-energizes the solenoid L of the reversing control RS to 
release and permit the valve FR (FIG. 5) to move to neutral position N in 
which the hydraulic fluid is recycled through passage G.sub.3 to the pump 
P without any pressure differential in the circuit C, and, leaving the 
winch brake B applied. 
Accordingly, with the speed of the lowering bucket adjustably held constant 
for all depths the desired earth penetration at the bottom may be 
controlled with a timed termination of the lowering after contact, or, the 
speed of lowering or both. 
The time to complete a closing of the bucket is adjustably measured in 
seconds by the digging relay DR. The slight overrun in the hoist line is 
taken up during the digging as adjustably controlled by the penetration 
time allowed by the timer relay TR so that the hoist line is quickly 
tightened and becomes weight bearing and the bucket will dig no deeper 
than desired. Automatically uniform repetitive results are accomplished 
with no delays. Thereby, constancy of bucket loading is assured. When 
switch DR1 is closed for the digging time cycle, switch DR2 is open 
thereby de-energizing through line 61 the self-holding switch LSR2 for the 
relay LSR, thereby opening switch LSR1 and closing switch LSR3. 
At the end of the timed digging cycle, and with timer relay TR already 
open, the self-holding digging relay DR is released, thereby opening its 
switch 1 and again closing its switch 2. Thereupon, 1) solenoid H of the 
reversing solenoid RS is energized through connections 80, 63 and 60 and 
rheostat RR, switches LSR3 and LSR1 and 2, the electromagnet EM is 
energized to pressurize cylinder CY and release the brake B and 
energization of the electromagnet BM is through connections 63 and 64, 
switch LSL1, both circuits being connected through connection 61 to switch 
DR2; 2) the vent solenoid VS recloses the vent valve VV to supply 
hydraulic pressure for the hoisting mode; and, 3) the brake electromagnet 
EM is also energized from connections 63 and 61 through switch LSL to 
release the brake B at the same time that the hoisting solenoid H of the 
reversing solenoid RS is energized. Thereafter, the reversing solenoid RS 
moves the flow reversing valve FR progressively from its neutral position 
N to the hoist position H to provide a gradual increasing flow of 
hydraulic fluid, and, the motor M smoothly picks up the bucket and its 
load. 
As the winch makes its first few turns the cam C1 releases the lower cam 
switch LCS for it to open its contacts 2 and closes its contacts 1 as 
shown in FIG. 4. Opening switch LCS 2 de-activates the bottom sensing 
circuits including the pressure responsive solenoids PR1 and PR2 before 
the bucket leaves the water. 
As the bucket moves upwardly with the switches DR1 and LC1 closed the 
further control of the bucket is transferred to the luff control LO 
through connections 65 and 78 since the upper control switch UCS is closed 
as the bucket approaches its upper hoist limit. The switches LCS1 and UCS 
serve essentially to assure that the bucket is at a luffing level before 
any luffing procedure is powered and triggered. 
With the now closed switch LCS 1 and the closing of the UCS switch by worm 
movement of the cam C1, the luffing mode is made ready and the rapid hoist 
and the pressurizing of the brake applicator BA is being maintained 
through closed switches LSL1 and LSL2, respectively, including parallel 
connections 80 and 60 for switch LSL2, and connections 60, 63 and the 
rheostat RR for switch LSL1. 
The cam-operated upper limit switch LSL comprises a pair of switches LSL1 
and LSL2 which may be micro switches that are opened sequentially by an 
inclined cam C2 (FIG. 6) carried on the worm drive WD. The switch LSL2 is 
the first to open and switch LSL1 is the last to open in the hoist mode. 
Then when switch LSL2 is opened by cam C2 the flow of electrical current to 
the hoist solenoid H is restricted to the rheostat RR which is adjustable 
to de-energize the hoist solenoid H progressively and permit it to 
gradually move to the neutral position N and thereby gradually restrain 
hydraulic flow to provide a slow down and a terminal creep that ultimately 
opens switch LSL1. Thereupon, the brake solenoid BS connected to 
connection 63 is de-enerigzed and the brake B is applied to the winch 44. 
During the hoisting operation the pressure tank PT has its pressure 
replenished for the next lowering and digging modes. 
Thereafter, the luff control LO takes over to actuate the luffing cylinders 
21, releases the bucket cylinder 32 to permit the bucket 16 to open, and 
then return the shear 12 to the bucket lowering position at the terminus 
of which a contact switch LS is closed in the luffing control that is in 
circuit with the connection 61 to energize the lowering switch relay LSR, 
and close switches LSR 1 and 2 and open switch LSR3. Closing the switch 
LSR 1 energizes the brake electromagnet EM through connection 64 to 
release the brake B while closing of switch LSR2 energizes the solenoid L 
of the reversing solenoid RS and provides a holding circuit through 
connection 73 between connection 61 and connection 62 which energizes the 
lowering solenoid L for the lowering mode. The opening of switch LSR3 
isolates switches LSL1 and 2 from connection 61. Then when the DR switch 2 
is opened the holding circuit 73 is released thereby releasing the relay 
LSR which in turn releases the reversing solenoid RS, returns it to its 
neutral position N and applies the brake B for the digging operation under 
the control of relay switch DR1 as already described. Opening switch LSR3 
cuts out any energization related to the hoisting mode. 
In order to assure release of the brake B regardless of the pressures in 
the conduit C, the high pressure in the tank PT is utilized as already 
described to release the brake B in a relation strictly timed with respect 
to the reversing solenoid RS. 
It may be noted that without the source of pressure in the pressure tank PT 
being present and the flow reverser FR in neutral position N with the 
brake B applied, the pressure in conduits PC and RC may equalize since the 
weight of the bucket is carried by the brake B. Under this condition the 
pressure switch PS may be operating to de-energize the electromagnet EM 
until the flow reverser FR moves from its neutral position N to either its 
lowering position L or hoist position N. Or, the hydraulic flow stoppage 
of the flow reversing valve FR in neutral position N might carry the 
weight of the loaded bucket 16 during the luffing operation without the 
brake B. However, it is preferred to control the application of the brake 
B by the separate circuit controls as described for a fail safe in event 
of a power failure. In any event, until the brake B is applied the weight 
of the bucket 16 and its load could be carried by the pressure in the 
conduit portion PC when the flow reverser FR is in neutral position N. 
Although interlocking circuit isolating switches or relays, including 
automatic safety relays AR1 and AR2, can be employed to de-energize 
circuits when not employed during a portion of the full cycle of operation 
it is preferred to segregate the lowering-digging circuit from the 
hoisting-luffing-opening controls by the utilization of the additional 
upper limit cam switch C2 and switches LSL and LSR 1 and 2 for separately 
applying the brake B and returning the flow reverser FR to neutral 
position N. Accordingly, the cam switches UCS and LCS preferably do not 
overlap in their closing although one may set up the back contacts of the 
other as shown for a certain stepped relationship as described. 
Furthermore, since the operation of the bottom-sensing-timing portion of 
the logic circuit illustrated is semi-isolated from the remainder of the 
circuit, it still will be operative to perform automatically when called 
upon to do so even though the main control MC is set for manual operation. 
It is arranged to perform as a unit and can also be actuated manually only 
after the bucket enters the water, the manual switch MS being connected in 
parallel with the cammed limit switch LCS2 for this purpose. The brake 
control circuit preferably is automatic at all times when the pressure 
switch PS is de-energized intentionally or otherwise in a fail-safe 
relation, the brake being applied whenever adequate bucket support 
pressure is absent in the pressure conduit PC as when there is either 
failure of electrical power or a diesel breakdown. This is accompanied 
automatically with the mechanical application of the brake B. Moreover, 
the digging relay DR is controlled solely through the bottom-sensing 
relays PR1 and PR2 in timed relation with the vent solenoid VS since it is 
undesirable for the bucket to dig-bury itself when not restrained at a 
fixed level by the winch brake B. Even upon power failure or emergency 
cut-off in any mode or operation or when the pressure switch PS is opened 
for any reason, the spring SS engaging the spool valve SV will enable the 
application of the winch brake B and will actuate the flow reversing means 
FR for a stand-by neutral position N.