A sprayer comprising: - a body provided with a base that can be applied to the mouth of a container for liquid and a delivery nozzle from which the liquid is sprayed, a pumping chamber being formed in said body, which is in communication with the inside of the container through an inlet hole and a dip tube, and with the delivery nozzle through an outlet hole and a duct (27, 28) having a substantially vertical portion disposed rearward of the pumping chamber and a substantially horizontal portion disposed in the upper part of the pumping chamber; - a trigger lever hinged to the body of the sprayer and to the stem of a plunger tightly slidable in said pumping chamber; - a one-way suction and delivery valve cooperating with said inlet hole and said outlet hole to control suction of the liquid from the container and delivery of the liquid towards the delivery nozzle following operation of said trigger lever; - an Upside Down USD device that allows operation of the sprayer in an upright Up position and in an upside-down Down position; said USD device comprising a chamber, closed at the top and integral with said body, disposed rearward of said pumping chamber, and having at least one hole that puts it into communication with the pumping chamber through said inlet hole, and at least one slot that puts it into communication directly with the inside of the container, means being provided to close said hole when the sprayer is in the Up position and to free it when it is in the Down position, allowing the liquid to flow from the inside of the container to the pumping chamber through said slots, characterized in that, said chamber is slanted backwards with respect to the vertical axis of the sprayer; and in that, said at least one slot is in communication with the inside of the liquid container through respective secondary channels which are formed between the chamber and an external chamber which surrounds it. - a body provided with a base that can be applied to the mouth of a container for liquid and a delivery nozzle from which the liquid is sprayed, a pumping chamber being formed in said body, which is in communication with the inside of the container through an inlet hole and a dip tube, and with the delivery nozzle through an outlet hole and a duct (27, 28) having a substantially vertical portion disposed rearward of the pumping chamber and a substantially horizontal portion disposed in the upper part of the pumping chamber; - a trigger lever hinged to the body of the sprayer and to the stem of a plunger tightly slidable in said pumping chamber; - a one-way suction and delivery valve cooperating with said inlet hole and said outlet hole to control suction of the liquid from the container and delivery of the liquid towards the delivery nozzle following operation of said trigger lever; - an Upside Down USD device that allows operation of the sprayer in an upright Up position and in an upside-down Down position; said USD device comprising a chamber, closed at the top and integral with said body, disposed rearward of said pumping chamber, and having at least one hole that puts it into communication with the pumping chamber through said inlet hole, and at least one slot that puts it into communication directly with the inside of the container, means being provided to close said hole when the sprayer is in the Up position and to free it when it is in the Down position, allowing the liquid to flow from the inside of the container to the pumping chamber through said slots,