Sprayer maintenance and calibration: testing rules, a step-by-step check and nozzle replacement

The testing rules in the UK

Under the Plant Protection Products (Sustainable Use) Regulations 2012, pesticide application equipment must be tested under the National Sprayer Testing Scheme (NSTS). The NSTS sets out the schedule:

• Boom sprayers over 3 m wide, air-blast sprayers, and train and aircraft sprayers: first test before the machine is five years old, then a re-test every three years.
• Booms of 3 m and under, slug pellet and micro-granular applicators, weed wipers, seed treatment and other specialist equipment: first test before five years old, then every six years.
• Knapsack, handheld and pedestrian equipment: no formal test, but it must be inspected by a competent person, repaired as needed and the inspection recorded.
• Assurance schemes go further: for Red Tractor Combinable Crops and Fresh Produce and for Scottish Quality Crops, sprayers over 3 m and air-blast sprayers need an annual test.

What else the regulations require

HSE's guidance on the 2012 Regulations also requires professional users to hold a recognised certificate of competence, to confine applications to the land or crop being treated, and to take reasonable precautions over storage, handling, filling, equipment cleaning and disposal. Professional users must keep records of pesticide applications for at least three years. The Code of Practice for using Plant Protection Products gives the detail on good practice, including keeping equipment calibrated and in good condition.

An NSTS test is a snapshot. Calibration is what keeps the sprayer accurate between tests, and it should be done at the start of each season, whenever nozzles or speeds change, and whenever the rate you see in the tank does not match the area sprayed.

A start-of-season service

Before calibrating, make sure the machine is in a fit state to calibrate. Work through it with clean water:

• Flush the tank, lines and boom, and clean every filter: suction, pressure, section and nozzle filters.
• Check hoses and clamps for cracks and leaks, and replace perished diaphragms or seals in the pump as the manual recommends.
• Check the pressure gauge against a test gauge; a gauge that reads wrong makes every later check wrong.
• Check the boom is level, straight and at the correct height above the target for your nozzles, and that the suspension and breakaways work.
• Check anti-drip valves shut off cleanly when the boom is turned off.
• Confirm the section control, flow meter and rate controller are working and calibrated to the manufacturer's procedure.
• Check the induction hopper, rinse nozzle and clean-water tank all work, so containers can be rinsed properly.

Calibrating step by step

The method below follows the standard extension approach, as set out by Colorado State University Extension, converted to metric units. You need a measuring jug, a stopwatch, a tape measure and clean water.

Step 1, measure forward speed: mark out a known distance, say 100 m, in the field you will spray, with the tank about half full. Time the run at your normal gear and engine speed. Speed in km/h is distance in metres divided by seconds, multiplied by 3.6.

Step 2, work out the nozzle output you need: required output (L/min) = target rate (L/ha) x speed (km/h) x nozzle spacing (m) / 600. For example, 100 L/ha at 12 km/h with nozzles every 0.5 m needs 100 x 12 x 0.5 / 600 = 1.0 L/min from each nozzle.

Step 3, measure actual output: at your working pressure, collect from several nozzles across each section for exactly one minute. Colorado State suggests checking that nozzle outputs sit within about 5% of the desired figure before spraying.

Step 4, adjust: small corrections are made with pressure, but remember flow changes with the square root of pressure, so doubling pressure raises output by only about 40% and also changes droplet size. Larger corrections need a different nozzle size or forward speed.

Step 5, check in the field: spray a measured area and compare the volume used with the volume expected. Recalibrate if they differ.

Nozzles: measure, do not trust the label

Nozzles wear from the moment they are used, and a worn orifice lets through more liquid and usually a less even pattern. Colorado State University Extension advises replacing nozzles where flow is 10% or more in error, and notes that brass nozzles can show 10-15% higher flow after 50 hours of use. Compare each nozzle's measured output with the manufacturer's catalogue figure at the same pressure; if several nozzles on the boom are out, replace the whole set so the boom is uniform.

Choose the nozzle type for the job and for drift. Low-drift and air-induction nozzles produce coarser droplets that drift less; some products need finer droplets for coverage. Follow the product label, which may specify spray quality or require drift-reducing technology near water. Our precision spraying and weed control guide covers section control and spot spraying in more depth.

Cleaning out and end-of-season care

Clean the sprayer thoroughly between products and at the end of each day, following the product label's cleaning instructions, which may specify a tank cleaner. Rinse the inside of the tank, run rinse water through the boom and nozzles, and clean filters. Dispose of washings in line with the label and the Code of Practice, on a suitable biobed or treated area, never near drains or watercourses.

At the end of the season, clean the sprayer fully, remove and store nozzles and filters, protect the pump and plumbing from frost according to the manufacturer's instructions, and note any worn parts to order before spring. Keep a service log alongside your spray records; together they show when the machine was last checked and help with an NSTS test. When comparing sprayers to buy, the FarmFleets machine search lets you check the tractor power and hydraulic capacity needed for a given tank and boom size.

Sources

Sources checked 2026-09-25

• National Sprayer Testing Scheme: Liquid application equipment test requirements — checked 2026-09-25
• HSE: Guidance on the Plant Protection Products (Sustainable Use) Regulations 2012 — checked 2026-09-25
• Welsh Government: Equipment inspection for pesticide users — checked 2026-09-25
• Colorado State University Extension: Pesticide sprayer calibration fundamentals — checked 2026-09-25

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