Flowserve Twin Screw Rotary - Manual (Page 13)

TWIN SCREW PUMPS. ORIGINAL USER INSTRUCTIONS. ENGLISH. 71569243 – 07/10
Page 10 of 53
®
3.3.2 Pumping Rotors
The pumping rotors (screws) are single start and
mounted two to a shaft in opposing configuration i.e.
one left and one right hand rotor to each shaft. The
intermeshing rotors mounted on drive and driven shaft
create a positive displacement pumping action inside
the pump body.
3.3.3 Shaft
The drive shaft is mounted on bearings with the
pumping rotor and timing gear mounted to the shaft. It
has a keyed drive end. The driven shaft is also
mounted on bearings with the pumping rotor and timing
gear mounted to the shaft.
3.3.4 Timing
Gears
The spur timing gears are mounted to the drive and
driven shafts with accurately located keys to maintain
the pumping rotors in mesh with no contact with each
other.
3.3.5
Pump bearings and lubrication
Antifriction radial and thrust bearings are mounted on
each shaft to support the induced loads. An oil bath is
provided at each end of the pump to lubricate the
bearings and timing gears.An oil site gage is supplied
in the bearing housings.
3.3.6 Stuffing box/seal housing
The stuffing box housing is doweled to both the pump
casing and the bearing housing to ensure proper
alignment. It can be supplied to fit standard packing or
different mechanical seals.
3.3.7 Shaft seal
The mechanical seals, attached to the pump shaft, seal
the pumped liquid from the environment. Gland packing
may be fitted as an option.
3.3.8 Driver
The driver is normally an electric motor. Different drive
configurations may be fitted such as internal
combustion engines, turbines, hydraulic motors etc
driving via couplings, belts, gearboxes, drive shafts etc.
3.3.9 Accessories
Accessories may be fitted when specified by the
customer.
3.4 Performance and operating limits
This product has been selected to meet the
specifications of your purchase order (See section 1.5
Duty conditions). The following data is included as
additional information to help with your installation. It is
typical, and factors such as temperature, materials, and
seal type may influence this data. If required, a
definitive statement for your particular application can
be obtained from Flowserve.
3.4.1 Operating limits
Pumped liquid temperature limits
up to+177 ºC (300 ºF)
Maximum ambient temperature up to +50 ºC (122 ºF)
Maximum soft solids in suspension up to 1 % by volume
Maximum pump speed Refer to the nameplate
3.4.2 Speed torque curves
To bring a rotary pump up to rated speed, the driver
must be capable of providing more torque at each
speed than required by the pump. Normally, this is not
a problem with standard induction or synchronous
motors provided the proper voltage is supplied at the
motor.
The margin between the available and required torque
affects the time it takes the unit to reach full speed. If
the torque required by the pump exceeds the torque
capability of the drive at any run-up speed, the unit will
not accelerate to full speed.
For pumps started at set system resistance conditions,
100 percent full speed torque can be calculated by
using the formula:
Torque (Nm) = 9545 Power (kW)
r/min
Torque (lbfx ft) = 5250 Power (hp)
r/min
Torque required by the pump at any other speed during
start-up can be determined from the curve above. Note
that the driver manufacturer usually bases 100 percent
torque on the design power of the driver and
consequently the speed-torque curves should be
plotted in torque units (e.g. Nm or lbf
× ft) instead of
percentage torque to avoid confusion.