I am talking about valves, and there is this specific valve which is cheap (not expensive), compact (not too big), easy to maintain (the valve is easy to clean and rarely ever needs to be repaired) and easy to 'seal tight' (meaning, it is easy to tighly seal the valve).
The sentence which I wrote was 'These valves are cheap, compact, easy to maintain and seal tight.'
My teacher highlighted this sentence saying something was wrong with the sentence structure and that 'easy to seal tight' is incorrect. Is it true that it is incorrect? If yes, how should I rephrase it so that the sentence structure is correct?