Lesson 12 - Control of Fluid Flow 3
This lesson will consider valve technology, which is used to control fluid flow. It will cover the control functions of on-off, and modulating flow control, together with a description of the various valve types which can achieve these functions. The lesson will conclude with thoughts on the issue of managing valve leakage to avoid cross-stream contamination.
Non-return Valve
Non-return valves (also known as check valves as they ‘check’ the flow from reversing) are used to ensure that flow can only occur in one direction and that reverse flow cannot occur.
The figure below shows the operating principle of a non-return valve. The valve consists of a disc fitted with a spring which forces it onto the lower port, ensuring that no downward flow, in this example, is possible. When upward flow commences, the flow overcomes the spring force and moves the disc upwards off the port so that flow can move around the disc.
Various types of non-return valves are available which use different movable valve elements, such as a disc (shown below), a ball or a flap.
Figure: Non-return valve