1-1/2hand sprayer need the rubber o-ring for groundwork

Question edited for clarity.

If they are small O-ring gaskets, an auto supplier carries them, if they are larger, a 'Fixings and Fasteners' outlet like Brafasco.

Otherwise, Amazon and others.

https://www.google.com/search?q=groundwork+pro+series+4+gallon+backpack+pump+sprayer+parts

..

Question edited for clarity, ' won't ' is a contraction of 'will not', 'the word 'want' is a request for something, they aren't interchangeable. ;>)

You sprayed has two handles, one on the wand and one on the pump.

Replacement wands are readily available. The pump is very simple in the way it works, there is a sealing gasket on the piston in the tube to create pressure and a non-return valve at the bottom of the tube to stop water flowing back. Check that they are clean and not obstructed.

GroundWork Sprayer parts

https://www.google.com/search?q=groundwork+sprayer+parts

..

pump or seal failing

https://www.youtube.com/watch?v=GXZisHxEq64

Try Parts Tree.com

I have a 4 gallon groundwork back pack sprayer. It will not pump up pressure. I took the cover off and found some broken plastic pieces that pump up the pressure. Cant find a parts diagram to identify them or order them.

you can get a spring for anything, you just need to know the size and type.. here is one site you maybe able to find one in your area.
http://www.leespring.com/uk_index.asp?CountryCode=011&utm_source=UK%20Google%20AdWords%20Campaigns&utm_medium=Google%20AdWords%20Search%20Network&utm_campaign=UK%20Products

need the hand wand were you pump up 3gal

chabunga offered really good info...except for the suggestion to use Vaseline on the 'O' ring. NEVER use Vaseline on anything rubber, because it is a petroleum based product and it will cause the ring to deteriorate. Use a non-petroleum based lubricant instead.