People who close things to keep air or water out.
Sealers are helpful because they keep things safe from air or water.
Examples:
The sealers closed the door tightly.
The food sealers keep the food fresh.
We need sealers to keep the water out of the boat.
The sealers make sure the jar is closed really well.
The sealers help keep the air out so the food doesn't go bad.
The sealers are like the gatekeepers for the food, keeping the bad stuff out.