All floor and frame pumps have a " check valve", usually at the base of the cylinder. It allows air to flow in one direction (pump to tire) but prevents back flow. I assume the one in yours is clogged or dirty and isn't seating properly. These are usually bearing balls or a flapper and lightly spring loaded in their seats. Try looking at the base of tyour pump under the pressure gauge or inside the hose attachment port.

Unlike rithem, I've had excellent service from Silca, Park and Meidai floor pumps. Clean yours up and it should work for years.