Yes, you can use a pressure washer to clean painted street benches without damaging the paint, but it depends on the condition of the paint and the settings you use. I would not recommend high pressure on old, flaking, or chalky paint because the spray will get under loose edges and peel it right off. If the paint is in good shape, a careful low to medium pressure wash is safe.
The safest approach is to use an electric pressure washer in the 1200 to 1900 PSI range. Gas machines can work too, but keep them on a low setting. Use a 25-degree or 40-degree nozzle tip and stay about 12 to 18 inches away from the surface. Before going all in, test a small hidden spot to make sure the paint is not lifting. Never use a red 0-degree tip on painted benches. That narrow jet can cut through paint and even leave marks on wood.
I like to pre-rinse the bench, apply a mild soap or automotive wash with a foam cannon or pump sprayer, let it sit for a few minutes, then rinse with wide sweeping passes. This lifts dirt and grime without having to rely on extreme pressure. If there are areas with bird droppings or tree sap, use a soft brush first instead of getting too close with the pressure washer.
For metal benches, check for rust spots or scratches before you start. Pressurized water can push moisture into exposed metal and cause more rust later. For wooden benches, keep pressure low and move constantly because wood fibers can fray or splinter if you linger too long.
After washing, let the bench dry completely and inspect the paint. If you notice any bare spots, touch them up with a matching outdoor paint or clear sealer. That small step keeps the bench protected and looking fresh. So yes, a pressure washer can be a safe tool for street benches when you treat it as a rinsing tool rather than a paint stripper.