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Introduction
A705-40-880 Issue B
1.5
Pressure relief valve (EDP250 and EDP400 only)
The EDP250 and EDP400 pumps have a pressure relief valve (
, item 26) fitted in a pipe between the pump-
outlet and the last stage of the pump. The valve is normally held closed by its own weight, but opens depending on
the pump-inlet pressure, as follows:
At pump-inlet pressures of 300 mbar (3 x 10
4
Pa) and above on the EDP250, and at pump-inlet pressures of
200 mbar (2.0 x 10
4
Pa) and above on the EDP400, the interstage pressure forces the valve open. This allows
process gases to pass directly from the second stage into the pump-outlet, without compression in the third
stage of the pump.
At pump-inlet pressures below those specified above, the interstage pressure is low and the valve is held
closed. Process gases pass through all stages of the pump; that is the process gases are compressed in the
third stage before they pass into the pump-outlet.
The pressure relief valve allows the pump to maximise pumping speed from atmospheric pressure down to 10 mbar
(1 x 10
3
Pa) and also prevents excessive electrical power consumption by the pump-motor when the pump starts.
1.6
Drive operation
1.6.1
Introduction
The EDP250 and EDP400 pumps have a torque limiter. The torque limiter provides mechanical protection for the
pumping mechanism, from excess liquid in the process gas stream.
The basic EDP80 and EDP160 pumps have a drive coupling, however you can order these pumps to be supplied with
a torque limiter fitted (refer to
). Refer to
for a description of the drive coupling operation,
for a description of the torque limiter operation. Refer to torque limiter amendment for
details of operation and maintenance.
1.6.2
Drive coupling operation
Note:
The EDP80 and EDP160 pumps do not need a torque limiter to protect the pumping mechanism from excess
liquid in the process gas stream. The electrical overload facility in the pump-motor provides this
protection.
The basic EDP80 and EDP160 pumps have a flexible drive coupling which transmits the drive from the pump-motor to
the pump rotors.
Refer to
. A coupling hub (15) is fitted to the pump shaft (16) and a coupling hub (5) is fitted to the motor
shaft (6).
1.6.3
Torque limiter operation
Refer to
. The pump-motor (12) drives the pump rotors through a torque limiter. When the torque required
to turn the pump rotors is excessive (for example, if the pump is accidentally flooded with process liquids), the
torque limiter automatically trips. When the torque limiter trips, it decouples the pump-motor from the pump, and
the pump-motor no longer drives the pump rotors. This prevents damage to the pumping mechanism.
When the torque limiter trips, the pump-motor will continue to operate, however there will be a significant fall in
the electrical current consumed by the pump-motor.
WARNING
If there is a risk that the electrical current monitor in your control system may not detect a torque
limiter trip, you must fit a rotation sensor to the pump.
