This can be due to a few different reasons. Here are a few examples:
1. The sprayer is left pressurised – ensure pressure is vented by pulling the pressure release valve after use.
2. Chemical is left in the sprayer – clean any chemical after use and flush through with clean water.
3. The chemical used is corrosive – only use branded garden chemicals suitable for treating garden pests or problems. Don’t use the sprayer as a spray gun for spraying paint thinners or any other chemical.
4. The sprayer has been left in the sun – this can cause the seals to dry out so ensure sprayer is put away after use and not left in direct sunlight.
5. The seals are not lubricated – moving seals, such as the piston in the pump and the o-rings in the tap need regular lubrication, as any chemical used may dry the seal out over time. Remove the necessary parts and lubricate with either silicon grease or Vaseline.