Xylem 19 001 200 R2 SILENT STORM VFD Pumping System - Manual (Page 33)

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DC Direct Current. Such as a battery. The voltage is stable, and does not oscillate
(at least intentionally).
Digital A simple ON/OFF condition. For example, the presence or lack of a 120VAC
signal on a wire is a digital condition.
DSR Downstream Relief Valve is used to limit the maximum allowable downstream
pressure.
Equal HP pumps Also referred to as interchangeable pumps. Defines which pumps are available to
start based on lowest run time. VSPs and XL pumps are defined in the PLC
program. An XL pump can be an equal HP pump, but it will not start as a lead
pump, because the lead pump will always be a VSP.
Filter A device used downstream of the pumps to clean the water being pumped into
the irrigation. These devices are typically self-cleaning, but require
hardware/software to self-clean.
Fixed speed Pumps run at a fixed RPM, defined by the motor windings and the frequency of
the line voltage (50/60 Hz).
Flooded suction A type of system where the pumps (usually centrifugal) are fed by a pond or
other body of water at very low pressure (atmosphere, or just a few feet of water
column). Pumps for these systems must be carefully selected for low NPSHR
(Net Positive Suction Head Requirements) or cavitation and pump damage can
occur. Low inlet pressure safety is an excellent choice for these systems.
Foot valve A device used primarily on horizontal lift applications to maintain pump prime.
Frequency (Hz) The number of oscillations per second of any system. Typically used to refer
to electrical systems, such as AC power line frequency, or variable speed drive
output frequency. This frequency defines the speed of an AC motor.
GPM Gallons per minute. Units of flow for US use.
HSS High speed switching. Starting pumps with a VFD to reduce inrush current and
provide pressure control, but able to switch over to fixed speed so that the VFD is
able to start another pump.
Input A way for a control system to detect real-world occurrences. These can be digital
or analog.
Inverter Another term for Variable Frequency Drive (VFD). Actually, more correctly
applied to the output circuitry of the drive, which converts DC voltage to AC
voltage.
Lag pump A pump used later in the pump sequence to support increasing irrigation demand
requirements. The term lag simply refers to the fact that it does not start first.
Lake fill (LLC) A circuit designed to keep a pond or lake at or above some minimum level
of water.
Lead groups Proprietary term used to describe the register(s) that defines which pumps on a
station are interchangeable in their pressure/flow characteristics.
Lead pump The pump in a lead group which is chosen by the controller to start first. This is
usually determined by finding the pump in the lead group with the lowest run-
time.