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.
Preface
During our study of fluid mechanics, we have only mentioned valve technology in passing. This is ironic because valves are everywhere and on brewery equipment of all sizes.
Therefore, we will now consider them in some detail, starting with the different functions that valves have, together with their flow characteristics. To conclude, we will examine the various types of valves and how to manage valve leakage.
Valve function
The function of a valve is quite simple: it is to control fluid flow. Control can mean different things to different people, but when it comes to valves, two particular control functions can be required:
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On-off flow control (often called open-closed flow)
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In this type of function, we require the valve to stop the flow completely or allow the flow to pass unhindered. So you can think of this type of valve function as all or nothing. As a simple example, a TV is either switched on or off by the on-off button: there is no in-between. As such, these valves are often called shut-off valves, for reasons that they shut the flow off.
Examples of such valve operation are commonplace in the brewery where flow paths need to be established from one vessel to another, via a hose or a hard pipeline.
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Modulating flow control (often called flow control)
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A modulating valve is one which controls the flow across a range of flows. So you can think of this function as similar to the volume control on a TV remote where the function allows the TV to be controlled from very quiet to very loud.
Examples of such applications include blending valves between high-gravity beer and dilution water, control of air/oxygen during wort oxygenation, and compressed gas supply during draught dispense.
This terminology can be confusing as on-off valves are also control valves, but within the industry, the term ‘control valve’ tends to mean a valve which controls flow to different levels, rather than only on-off.
Both types of flow control function have particular flow rate characteristics, which define the function.
Flow rate control
Before we consider flow rate control characteristics in detail, let us have a think about what we would want from a control valve. To do this, we can consider the most common control valve that we would have come across. We may think that it is the lauter tun sparge valve, the whirlpool draw-off valve, or even the fermenter outlet valve, but it is probably the cold-water tap in our kitchen sink.
What function (or functions) do you want from the cold-water tap (or valve) in our kitchen sink?
Give yourself 5-10 mins to think about this and then click ‘Next’ to continue with this lesson.