Scoop coupling in conveyor system

1. Prepared by
Jishnu V
Engineer, BHEL ISG

2. 1. WORKING PRINCIPLE OF A SCOOP
COUPLING
 Scoop coupling consists of two power transmitting
elements called Impeller and Runner, both having a
large number of straight radial vanes
 In a conveyor system the prime mover (motor) drives
the impeller. The runner is connected to the driven
machine or load (which is pulley via gearbox)
 In running condition, the working circuit of the scoop
coupling is filled with the oil and the impeller acts as
a centrifugal pump, creating oil flow radially
outward, which crosses the gap to the runner, which
acts as a turbine

3. 1. WORKING PRINCIPLE OF A SCOOP
COUPLING
 The oil flow gives up power as it return to the impeller
again and thus the cycle is repeated
 The input side of the scoop coupling connected to the
motor is known as the pump side and the output side
connected to the load is known as the turbine side
 Hence while running the power is transmitted from
the motor to driven machine through the rotating
forced vortex of oil
 As the fluid flow from impeller to runner there is slip
between these two parts.

4. 1. WORKING PRINCIPLE OF A SCOOP
COUPLING
 Mathematically Slip (S)= ωT –ωP
 Where ωT is the angular velocity of runner and ωP is
the angular velocity of impeller.
 Efficiency η= 1-S
 Due to the slip there is an energy loss which is
converted to the form of heat energy resulting in
heating of oil, which requires external cooling system
for oil
 The oil pump (gear pump) continuously supplies oil to
the coupling.

5. 1. WORKING PRINCIPLE OF A SCOOP
COUPLING
 The output speed of coupling can be changed by varying the slip,
which depends upon the oil quantity maintained in the working circuit
by changing the position of the scoop tube.

6. 2.0 SPEED CONTROL OF A SCOOP COUPLING
 If the scoop tube is moved into the rotating ring of oil,
it progressively removes the oil from the chamber and
working circuit / blocks the path of fluid flow and
discharges it into the sump.
 Inversely, moving the scoop tube from the oil ring
allows retaining more oil in the working circuit
 The scoop tube position can be changed from 0% to
100% to regulate the output speed of the coupling.
 In 0% position, the scoop tube is at FULL IN position
and does not allow oil level to build up in the coupling.

7. 2.0 SPEED CONTROL OF A SCOOP COUPLING
 At this position of scoop tube (0%), there is maximum
slip and minimum torque transmission.
 In 100% position, the scoop tube is at FULL OUT
position at which maximum oil is in the working
circuit.
 This (FULL OUT) gives maximum torque transmission
at minimum slip
 For intermediate position of the scoop tube,
intermediate value of slip and torque transmission is
obtained.

8. 2.0 SPEED CONTROL OF A SCOOP COUPLING

9. 2.0 SPEED CONTROL OF A SCOOP COUPLING
 A) No drive: (output shaft is stationary or scoop is in
full in position) Tip of the scoop tube is extended to a
radius slightly more than that of the working circuit
scoop trims all the oil from rotating members and
returns it to the sump for recirculation, the output
shaft is stationary.
 B) Intermediate speed: Scoop tip is withdrawn to an
intermediate radius. The working circuit and scoop
casing are partially filled to the level determined by
scoop tip. Output shaft and driven machine are
running at reduced speed

10. 3.0 OIL CIRCUIT

11. 3.0 OIL CIRCUIT

12. 3.0 OIL CIRCUIT
 The oil pump delivers oil from the sump (oil tank) to
the oil cooler (radiator type or shell and tube heat
exchanger type) through oil filter.
 From oil cooler oil goes into working circuit of the
Scoop Coupling. A small lube line is taken out from
the main oil line that provides oil to bearing.
 After transmitting power, the scoop tube collects oil
from working circuit and delivers back to the oil tank.
Also, some splashed oil in the coupling is returned to
the oil tank.

13. 3.0 OIL CIRCUIT
 The pressure switch and temperature switch give an
electrical trip signal to the control panel in case of oil
flow failure and temperature rise respectively.
 The manually operated butterfly valve (bypass valve)
allows either oil to flow into the working circuit or
totally bypasses back to the oil tank.
 When the fluid coupling is at rest, the oil is well below
the openings in the box through which the shafts pass
 When the scoop coupling starts operating, the oil
pump raises the oil from the sump and delivers it
through the heat exchanger

14. 3.0 OIL CIRCUIT
 The oil flows through the scoop housing into the
working circuit via drilled ports of the impeller. When
the coupling is running, the oil is escaping from the
working chamber into the scoop chamber via drilled
ports. The tip of the adjustable scoop, sliding radially
in the scoop housing, has its open tip projecting into
the scoop chamber. The movement of this scoop is
controlled externally and the radial position of the tip
determines the depth of oil permitted to remain in the
scoop chamber, and hence in the working circuit.

15. 3.0 OIL CIRCUIT
 The oil trimmed out of the scoop chamber by the
scoop tube returned to the sump for re-circulation.
 The speed out output shaft is determined by the
volume of oil in the working circuit and is controlled
by the depth of ring of oil in the scoop chamber and
regulated by the position of tip of scoop tube
 Full in of scoop  Depth of oil ring decreases  Less
oil in working circuit
 Retracting of scoop  Depth of oil ring increases 
More oil in working circuit

16. 3.0 OIL CIRCUIT

17. 4.0 MATERIAL OF CONSTRUCTION