Check valve and non return valve are same? 

Yes, check valve is one kind of automatic valve,also known as non return valve, one way valve, cut off valve, back pressure. So the check valve and the non return valve are the same valve. 

what is a non return valve(a check valve)?

check valve(non return valve) is one kind of industrial valve whose opening and closing part is a circular valve flap, and acts by its own weight and the medium pressure to block the back flow of the medium. The non return valve is an automatic valve, according to the movement mode of the non return valve, it can be divided into lift type non return valve(also called lift type check valve) and swing type non return valve(also called swing check valve). 

How does a non return valve work?

The lift type non return valve is similar in structure to the globe valve, except that it lacks the valve stem that drives the valve disc. The medium flows in from the inlet end(lower side) and flows out from the outlet end(upper side). when the inlet end pressure is greater than the sum of the weight of the disc and its flow resistance, the valve plate is opened. Conversely, the valve disc is closed when the medium flows back. 

The swing non return valve has a disc which is inclined and can rotate around the axis, and the working principle is similar to that of the lift check valve. The non return(check valve) is often used as the bottom valve of the pumping device, which can prevent the back-flow of water. The non return valve is used in combination with the globe valve, which can play the role of safety isolation. 

The disadvantage of non return valve is that its resistance is large and the sealing performance is poor when its closing.