Pump needs a new valve.
I have a very old Black & Decker Air Station. It's an electric air pump great for pumping up car tires etc. So despite being probably 20 years old, it still works great, with one catch. Like most pump valves, when you flip the lever back, it squishes a piece of rubber that squeezes the valve of the tube/wheel, which creates the seal. Well after 20 years, the rubber in my valve is completely dry-rotted. If I could get a new valve, this old pump would be as good as new. But as it stands now, you can't use the pump because all the air the pump tries to put in the tube, just escapes out of the pump's poor seal around the tube's valve.