I am installing a mixer tap in our kitchen sink. The current sink has two separate taps. From what I am aware, I would need to install a check valve in the hot and cold pipes before the tap hoses. I also want to install isolation valves for these tap. Is it possible to get a check valve with isolation valve built in? Otherwise, do I need to install one below the other and will single check valve do? The check valves have an arrow; I guess the arrow is to point towards the direction the water is meant to travel.