it does seem like a lot of liquid to be putting on a damp carpet. 1 litre of concentrate = 4 litres in the sprayer and that covers 25sqm. Maybe someone can enlighten me as 4 litres for what is an average size front room seems a bit much or have I got it completely wrong.
Below is copy and pasted from a suppliers site.
Chemspec Stainshield Professional is a water based Carpet and Upholstery Protector. Use on all wet cleanable fabrics to offer protection against oil, water based and dry soils.
Dilution rate can be altered depending on the job in hand. Dilute with more, or less, water depending on the pile density, thickness, fibre type, dampness of the item being protected. Dilute only with sufficient water to cover/penetrate the fibres - thus reducing drying times and giving the operator more control. As a starting guide, dilute 4:1 for carpets and 2:1 for upholstery.
Each litre of concentrate covers approximately 25 square metres of carpet (5 litres of concentrate covers around 125 square metres). Very economical at just over 50p per square metre.