Sourcing automatic DO controllers from China

Duty on dissolved oxygen controllers

Read from the UK Trade Tariff on 1 October 2026, heading 9032 covers automatic regulating or controlling instruments and apparatus. For a standalone dissolved oxygen controller, 9032 89 00 90 is the candidate line to confirm. It carries 2% duty for goods from China, as does the parts line 9032 90 00 90. Neither line lists an anti-dumping or countervailing measure or a suspension.

The UK Trade Tariff attaches an import control of fluorinated greenhouse gases to both lines. Ask the supplier whether the goods contain these gases and have your customs broker confirm the applicable requirement and declaration. The tariff entry alone does not establish what paperwork your particular controller needs.

Confirm the commodity code against the actual controller, probe and shipment contents. The table repeats the same controller line for different configurations; these are not separate tariff subdivisions. Do not assume every separately shipped probe is a controller part. See the automatic pH controller guide for the wider heading.

Specify the probe and aeration control loop

State whether the application is aquaculture, wastewater treatment or a process tank. Specify optical or electrochemical sensing, the measuring range and displayed units, temperature compensation, any salinity or pressure compensation, cable length, mounting arrangement and wetted materials. Agree how calibration is performed and which replacement caps, membranes or electrolyte the probe uses.

Define the set point, switching differential, alarm behaviour and output needed by the aerator or its control panel. Agree the response to a disconnected probe, an implausible reading and a power interruption. Test the quoted controller with its actual probe and the intended receiving equipment before approving production.

For mains-powered models, confirm the electrical safety requirements and applicable CE or UKCA evidence with the relevant authority, using the site's controller guide as a starting point. The electromagnetic compatibility rules cover electrical and electronic equipment liable to generate electromagnetic disturbance, subject to exceptions. Ask for model-specific supporting reports and use testing and certification support to review the configuration.

Worked duty example

Illustrative example, not a quote: Illustrative pilot batch of automatic dissolved oxygen controllers with matched probes under 9032 89 00 90, invoiced at £10,000 free on board, with £900 of freight and insurance to the UK. The customs value is £10,900. Duty at 2% is £218. Import VAT at 20% is charged on the customs value plus duty, £11,118, so it is £2,223.60. Import taxes total £2,441.60; a VAT-registered importer can usually reclaim the VAT, so the lasting cost is the £218 of duty. The import duty and VAT guide explains each step.

Inspection checklist

Probe and calibration: compare readings with a calibrated reference in representative water conditions, record stabilisation and repeatability, and check the supplied probe matches the approved sample.

Control response: change the oxygen condition across the agreed set point, check output direction and switching differential, and verify alarms and the agreed response to probe disconnection.

Installation: check terminals, cable glands, seals, mounting fittings and wetted materials against the order. Check cable identification and that replacement consumables fit.

Documents and traceability: match model labels and supplied reports to the shipment. For equipment within the hazardous-substance rules, products must show the importer's name or trademark and a contactable address on the product or packaging. Include these checks in quality inspection.

What goes wrong

A plausible oxygen reading does not prove the control loop works. A mismatched probe, damaged sensing cap, exhausted electrolyte or incorrect compensation setting can distort the reading. The controller may display correctly while its output operates in the wrong direction or cannot interface with the aeration panel.

Build acceptance around both measurement and output behaviour. Record the approved probe, firmware and settings, test recovery after a power interruption, and agree replacement consumables before shipment. Keep the probe protected during transport and inspect its sensing surface on arrival.

Cambridge China Bridge sources these products for UK businesses, checking the factory and the documents before shipment. See factory verification. For components and parts, see sourcing for manufacturers.