Usually a blocked nozzle, a lost prime, a kinked or short dip tube, or a failed valve - in that order.

Blockage is the commonest. Dried product crystallises in the nozzle, particularly with alkaline cleaners and anything left standing. Soaking the head in warm water usually clears it.

Loss of prime shows as pumping air. Repeated firm strokes with the tube submerged usually restores it; if not, air is leaking past a valve or the tube fitting.

The dip tube must reach the bottom and must not be kinked. A tube from a taller bottle bends against the base and draws nothing, and a tube from a shorter bottle stops working once the level drops.

Valves - usually a ball or a flap - stick with residue or wear. Some heads can be flushed clear; many are simply replaced.

A head that pumps liquid back into the bottle rather than out of the nozzle has a failed outlet valve and is finished.

Enough output to cover a surface in a few strokes, with a light enough action to use all day without hand fatigue.

Output per stroke varies substantially between heads. A high-output head is faster and wastes more product on small jobs; a low-output head gives fine control and takes more pulls.

Trigger effort is the ergonomic issue and is frequently ignored at purchase. Cleaning staff operate these hundreds of times a shift, and a stiff head causes real hand and forearm strain.

Heads with a mechanical advantage in the lever, or with a larger trigger surface, are noticeably easier over a shift.

Continuous-output and pre-compression heads reduce the number of pulls significantly and are worth the extra cost where spraying is a large part of the job.

Test before standardising - buy a small quantity, have staff use them for a week, then commit.

Yes - the seals decide which chemicals the head survives, and a mismatched seal fails quickly and confusingly.

Standard trigger heads use elastomer seals and gaskets chosen for general detergents and disinfectants, which covers most cleaning.

Solvents, strong acids, strong alkalis and some disinfectant actives swell or harden those seals. The symptoms are a head that loses prime, leaks around the trigger, or becomes stiff.

Because the failure looks like an ordinary fault, the underlying incompatibility often goes unrecognised and the replacement head fails the same way.

Chemically resistant heads use different seal and valve materials and cost more; they are the correct answer for aggressive products.

Check the chemical against the head's stated compatibility rather than assuming - suppliers publish this, and it is the difference between a head lasting a year and a week.

Generally no - trigger heads are designed for water-thin solutions, and viscosity is a hard limit rather than a matter of effort.

The pump draws liquid up a narrow tube and forces it through a small orifice. A viscous product will not flow through either at any reasonable trigger force.

The symptoms are a head that pumps hard and delivers little, or that appears to work and then blocks.

Products that thicken on standing, gels, and anything with suspended solids all cause this.

Where a thicker product must be applied by spray, foaming heads and pump-up sprayers with larger orifices handle more, and some products are supplied in their own dispensing container for exactly this reason.

Diluting to reduce viscosity changes the product's performance and should only be done if the label permits it.

Flush with clean water after use with any aggressive product, store with the nozzle closed, and replace rather than repair.

Flushing prevents residue drying in the nozzle and the valves, which is the cause of most blockages. It matters most with alkaline cleaners, chlorine products and anything that crystallises.

Closing the nozzle in transit stops leaks in a caddy and stops the head drying out.

Soaking a blocked head in warm water usually restores it, and a fine wire will clear a nozzle - though forcing anything into the orifice can enlarge it and ruin the spray pattern.

Heads are inexpensive and are consumables. Keeping a small stock means a failed head does not take a bottle out of service.

Do not move a head between chemicals without flushing - residue transfer causes both performance and safety problems.

Cone for covering an area evenly, jet for reach and for directing product into a specific spot, and off for transport.

A cone or fan distributes product over a surface, which is what most cleaning needs and what keeps a surface wet for a disinfectant's contact time.

A jet carries further and concentrates the product, which suits reaching under rims, into corners and up to high surfaces without a ladder.

The off position locks the nozzle and prevents the bottle discharging in a caddy or a vehicle. It is worth training staff to use it, because a bottle that empties itself in a caddy is both a loss and a hazard.

For occupied spaces, spraying onto a cloth rather than into the air reduces inhalation exposure substantially - a technique matter rather than a setting.

Adjustable nozzles wear and eventually will not hold a setting, which is an end-of-life sign.

Only where the neck size and the dip tube length match - which is the argument for standardising both across the site.

Neck diameter and thread must match or the head will not seal, and a forced cross-thread cracks the bottle neck.

Dip tube length is the part most often overlooked. Too long and it kinks against the base; too short and it stops drawing before the bottle is empty. Tubes can usually be trimmed, but not lengthened.

Standardising the neck size across the site means any head fits any bottle, and failed heads can be replaced from stock rather than discarding the bottle too.

Matching the chemical supplier's own bottle finish means their empties can be reused as spares.

Where heads are moved between bottles, flush them first - residue transfer between chemicals is both a performance and a safety issue.