A valve assembly is configured to regulate the flow of an isolated fluid therethrough and includes a first valve stage configured to control the flow of a first fluid through a first fluid circuit, and a second valve stage configured to control the flow of a second fluid through a second fluid circuit. The first valve stage is connected to the second valve stage such that the first fluid acts on the second valve stage to move the second valve stage between open and closed positions. The second fluid flowing through the second valve stage is also isolated from the first fluid flowing through the first valve stage.