Pump VFD: Constant-Pressure Pump Inverters

Built for pumps, not adapted to them

The AU620 documentation describes a drive designed to manage a water pump's performance across the conditions a water supply system actually presents. Its published feature set is pump-specific: protection against phase loss, overload, overvoltage and undervoltage; automatic restart when power and water return; intelligent anti-freeze and anti-rust protection; automatic shutdown on water shortage or a burst pipe; and compatibility with both permanent-magnet synchronous and asynchronous motors — one machine for two motor types. The AU820 and the backpack-format M820 publish the same feature set in an IP54 enclosure that mounts on the pump itself.

Dual-master multi-pump control

For booster sets, the documented system architecture matters more than any single drive. In the AU620 system, the master drive reads the pipe-network pressure and controls the auxiliary drives over an extensible RS485 link — one master can control up to four auxiliaries. The master monitors each auxiliary in real time: if an auxiliary fails it is skipped and the next one starts; if the master fails, the standby master takes over automatically. Master and auxiliaries can also alternate on a timed rotation so the pumps wear evenly. The YS620 publishes the same dual-master concept, with two masters and up to four auxiliaries in its selection documentation.

Published ratings — AU620 class

Control mode	V/F control
Starting torque	0.5 Hz / 100%
Speed range / precision	1:100; speed-holding precision ±1.0% (AU620)
Overload capability	150% of rated current for 60 s; 180% for 1 s
Input voltage	220 V AC ±15% and 380 V ±15%, single- and three-phase models
Output frequency	0–200 Hz (AU620)
Pressure inputs	Remote pressure gauge 0–10 V; pressure transducer 4–20 mA (AU620)
Protection functions	Water-shortage stop with timed auto-restart attempts; high-pressure alarm stop; automatic energy-saving running at light load
Environment	−10 °C to +40 °C; humidity ≤95% RH non-condensing; altitude below 1,000 m (derating above)

The YS620 selection table publishes models from 0.75 kW to 7.5 kW in single-phase-in/three-phase-out 220 V and three-phase 380 V versions, with the same 0–200 Hz output and 1:100 speed range. For constant-pressure booster sets specifically, see the booster pump VFD page; for borehole and well pumps, the submersible pump VFD page; and for the sealed IP54/IP65 formats, the waterproof pump VFD page. Solar-powered pumping is a separate line — the solar pump inverters.

Frequently asked questions

How many pumps can one system run?

In the AU620 documentation, one master drive controls up to four auxiliary drives over RS485, with a standby master able to take over. The YS620 documents two masters plus up to four auxiliaries. For larger sets, send the pump count with your enquiry and ask what configuration can be offered.

Does the drive protect against dry running?

Yes, as documented: if pipe pressure falls below the set water-shortage value, the system stops automatically, retries after a set period, and stays stopped if pressure does not recover — protecting the pump from idle running.

Which pressure sensors are supported?

The published AU620 peripheral interface accepts a remote pressure gauge signal (0–10 V) and a pressure transducer (4–20 mA), alongside programmable digital and analogue inputs.