A pump comprising: a body which defines an inlet and an outlet to allow flow of a liquid, wherein the pump has a suction side (S) around the inlet and a pressure side (P) around the outlet ; an impeller positioned downstream of the inlet ; a backflow opening in fluid communication with the inlet and the outlet ; and a first valve operatively coupled with the backflow opening to selectively open the backflow opening , wherein the first valve defines a first end and a second end , and wherein the first valve includes a first valve housing , wherein a first valve body is biasingly coupled by a first spring within the first valve housing around the second end , and wherein the first valve body is adapted to move the first spring to a first compressed state to disallow flow of the liquid through the first valve , and the first valve body is adapted to move the first spring to a first uncompressed state to allow flow of the liquid through the first valve ; characterized in that: a second valve disposed within the first valve , wherein the second valve has a second valve body , wherein the second valve body is biasingly coupled by a second spring within the first valve body , wherein the second valve body is adapted to move the second spring to a second compressed state to allow flow of the liquid through the second valve , and the second valve body is adapted to move the second spring to a second uncompressed state to disallow flow of the liquid through the second valve . a body which defines an inlet and an outlet to allow flow of a liquid, wherein the pump has a suction side (S) around the inlet and a pressure side (P) around the outlet ; an impeller positioned downstream of the inlet ; a backflow opening in fluid communication with the inlet and the outlet ; and a first valve operatively coupled with the backflow opening to selectively open the backflow opening , wherein the first valve defines a first end and a second end , and wherein the first valve includes a first valve housing , wherein a first valve body is biasingly coupled by a first spring within the first valve housing around the second end , and wherein the first valve body is adapted to move the first spring to a first compressed state to disallow flow of the liquid through the first valve , and the first valve body is adapted to move the first spring to a first uncompressed state to allow flow of the liquid through the first valve ; characterized in that: a second valve disposed within the first valve , wherein the second valve has a second valve body , wherein the second valve body is biasingly coupled by a second spring within the first valve body , wherein the second valve body is adapted to move the second spring to a second compressed state to allow flow of the liquid through the second valve , and the second valve body is adapted to move the second spring to a second uncompressed state to disallow flow of the liquid through the second valve . a second valve disposed within the first valve , wherein the second valve has a second valve body , wherein the second valve body is biasingly coupled by a second spring within the first valve body , wherein the second valve body is adapted to move the second spring to a second compressed state to allow flow of the liquid through the second valve , and the second valve body is adapted to move the second spring to a second uncompressed state to disallow flow of the liquid through the second valve . <EOS>