Tetra whisper fish tank air pump help?

Hi i just bought a tetra whisper air pump for my 10 gallon fish tank. The pump can be used up to ten gallons. I recently bought a volcano air bubble decoration for my tank and hooked it up to the air pump. it worked fine. The pump also comes with a plastic t valve since there is only one air port. I just bought a moving ship wreck air bubble decoration and when i hook both tubes up to the valve, only the ship wreck works not the volcano. But when i hold the line going to the ship wreck so no air can get to it, the volcano one works perfectly. Is my pump not strong enough, or did i do something wrong? thanks