If you have a Westpack wand with the soft touch valve, you will probably find that after a while the spring will break and then you will have to buy the repair kit...probably about £10 inc delivery.
You can buy the stainless springs on their own for £2.50 a piece....min charge £15 per order = 6 springs = 10 years use.
Common sense to just buy the springs to keep on the van and when the spring breaks and water is p*ssing all over custys house you have a replacement.

Part no: D21680 from Springmasters. 12mm long x 6mm wide x 1mm wire dia