Why do my valves continue to stick?

Ok, I started with and Eastman beginner trumpet. The valves stuck on that. Then, I moved to another brand, but forgot the name. The valves also stuck. I am now on a Yamaha. It says,"YTR200ADII" and beneath that it says, "V63025." This trumpet also sticks. I have sent it to a repair shop multiple times and in the end, it sticks. I hold my left hand like this: I have my thumb between my first and second valve, my pinkie on top of the hook thing, and my finger straight down on the valves. I would like to know what to do at this point. Do I take everything apart and wash it with warm water?