The orifice creates the pressure. For a given flow, a smaller hole means higher pressure, and a larger hole means lower - the pump does not decide it.

This is the single most misunderstood point about pressure washers. A machine rated at a certain pressure only achieves it with the correct nozzle size fitted.

Fit a nozzle that is too large and pressure collapses. The machine sounds normal, water comes out, and cleaning performance is poor for no visible reason. This is exactly what a worn nozzle does gradually.

Fit one that is too small and pressure rises beyond the machine's rating, loading the pump, opening the unloader and heating water in bypass.

Nozzle sizing is expressed as a numbered orifice matched to a machine's flow. When buying replacements, the flow rate of the machine is the number that matters - not its pressure rating.

They indicate spray angle, and the convention is broadly consistent across manufacturers - narrow angles for cutting, wide for rinsing, and a separate colour for low-pressure chemical application.

A zero-degree pencil jet concentrates everything into a point. It removes stubborn spots and damages almost any surface it lingers on; many professionals avoid carrying one.

Narrow fans are the general heavy-cleaning choice for hard surfaces such as concrete.

Medium fans handle most general cleaning and are what stays on the lance most of the day.

Wide fans rinse, and are the safe choice for painted surfaces, vehicles and anything delicate.

The low-pressure chemical nozzle has a much larger orifice, which drops pressure enough for a downstream injector to draw detergent. Trying to apply chemical without it simply will not work.

Colours are conventional rather than mandated, so confirm against the supplier's own chart.

For hard, stubborn soils on robust surfaces - and never on anything soft, painted, jointed or delicate.

A turbo nozzle spins a zero-degree jet in a cone, so the surface receives the impact of a pencil jet while the tool covers a circle. On concrete, stone and heavily soiled hard surfaces it removes what a fan nozzle leaves behind.

That same intensity destroys timber, render, soft brick, mortar joints and paintwork. It will also cut through jointing sand and force water into places it should not go.

Keep it moving. A rotary jet held still cuts a visible circle into the surface within seconds.

Turbo nozzles wear faster than fixed ones because of the bearing, and a worn one loses rotation and becomes an uncontrolled pencil jet - which is worth knowing before the first mark appears.

Standard lances for general work, extended and telescopic for height, bent for undersides, gutter lances for roofline work and foam lances for chemical.

A standard lance gives the working length most jobs need and keeps the reaction force manageable.

Extended and telescopic lances reach eaves, upper walls and high plant without a ladder, which is a genuine safety improvement - pressure washing from a ladder is hazardous because of the reaction force. The longer the lance, the heavier it feels and the more support it needs.

Bent or angled lances reach vehicle underbodies, the undersides of machinery and behind obstructions.

Gutter lances are curved with a rearward-facing jet to flush guttering from ground level, usually on a telescopic pole.

Foam lances hold a chemical reservoir and produce thick foam that clings while it dwells, which is what makes chemical effective on vertical surfaces.

A safety catch, a comfortable trigger that does not require constant force, and a swivel where the hose enters.

The safety catch prevents accidental discharge when the gun is set down or carried, and no other feature on the gun matters as much.

Trigger effort matters over a working day. A stiff trigger causes hand fatigue and leads operators to jam it open, defeating the total-stop system and leaving the pump running in bypass.

A swivel inlet stops the hose from twisting as the operator turns, which prolongs hose life and makes the tool much less tiring to use.

Guns are rated for pressure and temperature. A gun rated for cold water only will fail on a hot machine, and the failure mode is scalding rather than inconvenience.

Check the coupling standard before buying, since a gun that does not fit the hose and lance is useless.

The machine seems weaker, the fan looks wider or uneven, and the pressure gauge reads lower for the same setting.

Nozzles erode from the inside as water and grit pass through. The orifice enlarges, pressure falls, and because it happens over weeks the operator compensates without realising.

The clearest symptom is the spray pattern: a fan that has become wider, ragged at the edges, or asymmetric. A new nozzle held alongside makes the difference obvious.

On machines with a gauge, pressure at the same nozzle falling over time is direct evidence.

The remedy is cheap. Nozzles cost very little and replacing the set restores the machine's designed performance instantly - it is the highest-return maintenance in the whole category.

Blockages are different: a partially blocked nozzle gives a distorted or split pattern and can usually be cleared with the supplied wire rather than replaced.

Through a downstream injector with the low-pressure nozzle fitted, or from a foam lance with its own reservoir.

Downstream injection draws detergent into the water after the pump, so the chemical never passes through the pump seals. It only draws when pressure is low, which is why the wide low-pressure nozzle must be fitted for it to work at all.

Upstream or high-pressure injection exists but exposes the pump to the chemical, and not all pumps or chemicals tolerate it.

A foam lance carries its own bottle and mixes air in to produce thick foam. Foam clings to vertical surfaces instead of running off, which is what gives the chemical time to work.

Dwell time is the point of the exercise. Apply, wait several minutes without letting it dry, then rinse at pressure with the working nozzle refitted.

Flush the injector with clean water afterwards, especially after acidic products.