The QDP pumps operate at pressures between atmospheric and ultimate vacuum with no
lubricating or sealing fluid in the pumping chamber. This ensures a clean pumping system
without back-migration of oil into the system being evacuated.
QDP pumps have enclosed, water-cooled motors and are therefore suitable for applications in
clean environments where fan cooling is unacceptable.
The QDP Pump
The QDP pumps are each fitted with a gas system, exhaust-silencer and check-valve. The pump
is fixed to the framework by vibration isolators. The framework has castors and levelling feet.
The QDP pumps are four-stage, positive displacement rotary pumps in which pairs of
intermeshing rotors (of different profiles mounted on common shafts) are held in correct phase
relation by a pair of timing-gears. The timing-gears and the adjacent double-row angular contact
ball-bearings, are oil lubricated.
The pump shafts and rotors are made from cast-iron. The internal and external shaft-seals on
the motor drive-shaft are made of polytetrafluoroethylene (PTFE). Bearings are located on the
high vacuum end of the shaft, near to the pump-inlet. These bearings are packed with
perfluoropolyether (PFPE) grease.
QDP pumps have a gas system of stainless steel pipelines (see Figure 1) which allows nitrogen
to be delivered to the following points :
- Shaft-seal purge
- 2/3-interstage purge
- 3/4-interstage purge.
You will connect your nitrogen supplies to this gas system through connectors on the gas services
Temperature control system
The low vacuum stage of the pump has an indirect cooling system, all other stages are air-cooled
by natural convection and radiation. In the secondary circuit of the indirect cooling system,
coolant circulates around the pump-body by natural convection. In the primary circuit,
cooling-water is circulated through copper coils to extract heat from the coolant. In operation,
the pump is maintained at a constant temperature by a thermostatic control-valve (TCV) which
controls the supply of cooling-water to the primary circuit in the pump.
The pump-motor is cooled by water flowing through a cooling jacket which surrounds the motor.
The pump-motor cooling circuit is separate from the pump cooling circuit. The cooling-water
supply and return pipelines are connected to the pump by connectors on the water services panel
at one end of the pump
The cooling-water manifold on the pump distributes the cooling-water to the pump cooling
circuit and to the pump-motor cooling circuit (and to the QMB pump-motor cooling circuit, if a
QMB pump is fitted). When a QMB pump is not fitted, the flow of cooling-water to the QDP
pump-motor is greater than the minimum required flow. When a QMB pump is fitted, the
cooling-water flow is distributed equally between the two pump-motors and the overall flow
requirement for the pumping combination increases
Two thermal snap-switches are fitted to the pump-body. One of these snap-switches (the
warning switch) opens at 88 oC and the other snap-switch (the shut-down switch) opens at 95 oC.
Use the warning switch to provide a warning that the pump is too hot. Use the shut-down switch
to shut down the pump.
Three motor-protection thermistors are fitted to the pump-motor (one on each winding). These
thermistors are solid-state devices which have an electrical resistance of 100 to 500 W at normal
pump-motor operational temperature. When the pump-motor is too hot, the electrical resistance
rises quickly to 3000 W. The thermistors are connected in series and you can use the output of
the thermistors to shut down the pump because the motor is too hot.
The QDP pumps have universal voltage and frequency motors. These motors are supplied
configured for ‘low voltage’ operation (200-208 V at 50 Hz or 200-230 V at 60 Hz).
You will connect your electrical supply cable to the pump through a cable-gland on the
terminal-box on the end of the pump-motor (see Figure 10). You must use a suitably rated
contactor (see Section 2.4). The electrical services panel has a connector to connect the outputs
of the thermal snap-switches and the motor-protection thermistors to your control equipment.
The pump outlet is connected to an exhaust-silencer, which is below the pump. The outlet also
has a port which allows gearbox vent gases to join the main exhaust stream (see Figure 1). The
exhaust-silencer attenuates the pulses in the exhaust pressure and reduces pump-induced
resonance in your exhaust-extraction system. The outlet of the silencer has a check-valve which
prevents the suck-back of exhaust vapors after the pump is shut down. The valve also provides
additional attenuation of the pulses in the exhaust pressure.
A number of accessories are available for the QDP pump; use these to configure the pumps for