Eng
lish (US)
16
7.1 Pump operation protection
CR-H MAGdrive pumps must not operate at conditions outside
the operating range. Protection functions will either control
operation or stop the pump if the limits for the operating
conditions are exceeded.
7.1.1 Low flow (bypass) protection
Minimum flow rate through the pump is 10 % of the nominal flow
rate. Protect the pump against operation with too low flow by
installing a bypass and vent line. The bypass and vent line must
be connected in the following way:
• to the pump head
• to a reservoir using a dedicated bypass connection.
Install a flow restriction of permanent (orifice) type in the bypass
and vent line. The pressure drop of the flow restriction must allow
the minimum pump flow rate through the bypass and vent line:
• For variable speed pumps, the pressure drop is the differential
pressure setpoint.
The bypass and vent line flow is not to be controlled with a
solenoid valve. The bypass and vent line vents the pump when
the pump is not operational.
7.1.2 Low head protection
Generally, the minimum differential pressure is to be 10 psi below
the setpoint differential pressure. The absolute minimum
differential pressure is 20 % of the closed-valve pressure at 60
hz.
The maximum pump head can be found on the pump
performance curve.
Stop the pump if the pressure difference becomes lower than the
minimum pressure difference allowed for a maximum of 20 %.
Automatic restarts are allowed after a stand still period of
minimum 90 %. Limit the number of consecutive automatic restart
attempts to five.
7.1.3 Available NPSH protection
Ensure that the required NPSH (NPSHR) is available under all
operating conditions. Install a liquid level switch or transmitter in
the separator at a minimum liquid column height corresponding to
the NPSHr plus 2 ft. Add the switch function of this device to the
pump safety chain (terminals 18 and 20). Stop the pump
immediately if the liquid level becomes too low.
7.1.4 High motor current protection
Protect the pump motor from operating with too high motor
current during startup or during regular operation. Program the
variable frequency drive to stop the pump immediately if the
motor current is too high.
In order to ensure the optimum protection of the MAGdrive motor,
the motor protection must be set in accordance with the following
guidelines:
1. Set the overload protection to the rated service factor current
of the motor.
7.1.5 High/Low motor speeds protection
When operating the pumps with variable speed using a frequency
converter, limit the minimum and maximum motor supply
frequencies.
For pumps designed for 60 Hz operation the motor supply
frequency must be between 30 Hz and 60 Hz.
When controlling the pump speed according to constant
differential pressure, the minimum motor supply frequency must
be above 30 Hz.
7.1.6 Other relevant protection functions
Other special protection functions may be required to prevent
operation of pumps at conditions that can damage the pump. The
need for further pump protection must be evaluated according to
the application.
Maintain a stable reservoir or vessel pressure by limiting the
maximum pull-down rate.
Limit the temperature pull-down rate of the reservoir or vessel
during pump operation to 1.1 F/min. Prevent pumps from
operating when the separator pressure is more than 9 °F above
the system setpoint.
Dry running
Prevent pumps from operating at conditions where there is a risk
of dry running.
7.1.7 Operation
During regular operation the pump protection functions will keep
the pump within its acceptable range. If one or more of the
protection functions are activated the root cause must be
investigated and found. Failure to find the root cause for the
pump stop may result in damages to the pump.
For some new system types it is customary to inspect strainers
and components after the first 100 hours of operation and clean
the strainers to prevent them from reducing or blocking the flow.
Depending on the conditions and operating time, make the
following checks at regular intervals:
• Check that the pump meets the required performance and is
operating smoothly and quietly.
• Check that there are no leaks.
• Check that the motor is not overheating.
• Remove and clean all strainers or filters in the system.
• Check that the tripping function of the motor overload
protection works.
• Check the operation of all controls.
The pump shaft must be manually rotated or run for short periods
of time at monthly intervals if the pump is out of service.
Summary of Contents for CRN-H MAGdrive
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