A hand pump for inflating rafts or similar inflatables has a first piston with a relatively low pumping volume which is capable of pumping relatively small volumes of air into a raft as the raft becomes full and is approaching its maximum pressure, and a second piston with a larger pumping volume that can pump larger volumes of air into a raft when it is empty or only partially filled. Both pistons are operated with a single plunger. When the plunger is rotated in a first direction to a first position a locking mechanism allows it to operate only the first piston, and when the plunger is rotated in a second direction to a second position the locking mechanism allows it to operate only the second piston.