This is how I modified a knapsack sprayer and a sack truck into a back saving wheeled sprayer.
I have a back problem that is aggravated by using a knapsack sprayer, the weeds still grow and need to be sprayed but my back is not capable of the weight of 20kg of water plus having to carry it around the rough ground.
The solution was to combine the sprayer with a sack truck so the sprayer could be easily wheeled around.
A new pump handle and link arm where fabricated out of flat bar and 12mm dia round bar. the fabrication was kept simple and is held in place with R clips so the sack truck and the sprayer can be returned to their original selves in a few minutes.
Thanks for looking and I hope that this idea is of use to some people.