Abstract: A nozzle suitable for use with a device for removal of deposits from contaminated surfaces, such as a sootblower in a heat recovery boiler, is designed to avoid normal shock wave formation, and hence energy dissipation, by achieving a condition whereby, the emergent steam pressure (p.sub.e) is related to the ambient pressure (p.sub.oo) by the relationship p.sub.e /p.sub.oo <about 2, preferably about 1. A compact design achieving this result and able to function over a wide range of flow rates comprises a cylindrical body with a downstream convergent outlet and a rounded-head conical insert located axially in the body with its maximum dimension generally coinciding with the commencement of convergence of the outlet and extending through the outlet.