I have the water line for the AC swamp cooler running from under the sink and the water will not shut off even though I turned knob all the way off. Is the shut off valve the part I need to replace?

i have the water line for the AC swamp cooler running from under the sink and the water will not shut off even though I turned knob all the way off. is the shut off valve the part i need to replace?

Are we talking about a angle stop ? (see image)