A pump head of an air pump includes a head including an outer body, a handle, and an end cap. The outer body includes a compartment extending therein. The handle is connected to a first end of the outer body. The end cap is connected to a second end of the outer body. A retaining device is received by the compartment and includes a seat actuated by the handle. An air seal ring is received by the compartment and is selectively compressed by the seat. The seat includes a cavity extending therein, at least one slot extending radially from the cavity and through the seat, and at least one retaining arm extending between two sides of the at least one slot and resiliently swingable. The air seal ring has an outer periphery section curved radially inwardly with respect to other periphery sections along a longitudinal length thereof.