This will, of course, depend on the product you’ve purchased and you should always refer to the manufacturer’s manual for instructions.
On the whole, modern backpack sprayers are designed for ease of maintenance and only a few simple guidelines need to be followed to keep the equipment in optimum condition:
Read the service manual to check for particular requirements for your sprayer.
After each spraying job, clean the inside and outside of the sprayer thoroughly, including disassembling and cleaning each part meticulously, according to manufacturer’s instructions.
Check for wear and correct fitting of the ‘O’ rings - having a few spares on hand is advisable for quick and easy replacement.
Reassemble the unit and store in a clean and dry area.
Note that plastic sprayers should not be left out in the sun as they are affected by UV radiation which will harm the plastic and shorten the useful life of the equipment.