All About Diaphragm Valves
Basic engineering devices such as valves contribute to almost every complex system. These mechanical/electromechanical devices regulate media flow and come in dozens of unique varieties; to see all the different types of valves, visit our understanding valves article. The diaphragm valve will be the focus of this article, and we will explore what they are, how they work, and the different types available. Through this investigation, this article should help decide if diaphragm valves could be useful, and how to choose the correct version for a given application.
What are diaphragm valves?
Diaphragm valves are bi-directional, on-off throttle valves. They are used to control fluid flow by regulating the area with which media can enter and exit the valve, effectively changing its speed and velocity. They are so-called “diaphragm” valves because a thin, flexible membrane is used to control the opening and closing of the valve. They can be made with metal such as stainless steel, plastic, and even single-use materials. Diaphragm valves are like pinch valves but they use a linear compressor which pushes the thin diaphragm into contact with the valve body. They offer discrete and variable pressure control and can be both manually and automatically actuated. Diaphragm valves are clean, leak-proof, easy to maintain, safe, and effective valves that are best suited for moderate pressure & temperature applications which require stop/start fluid control.
How do diaphragm valves work?
Diaphragm valves are simple in construction and operation. As shown in Figure 2, a valve actuator is in contact with the inner membrane (or “diaphragm”) of the valve in its open position. When the user desires the valve to be shut, the actuator is pressed and/or turned and the membrane is pushed into the edge of the solid damn, closing the valve. Certain diaphragm valves can also have half open/restricted positions where the membrane is partially closed, allowing a throttled flow through the valve. In the next section, we will examine the broad categories of diaphragm valves and where they are most useful.
It’s a diaphragm valve but not as we know it
Bürkert’s Robolux diaphragm valve addresses wastage and dead volume with an innovative 3-way design that eliminates dead legs and any need for heavy valve block assemblies. Process Industry Forum spoke to Ian Webster, Field Segment Manager for Hygienic Processing at Bürkert, to find out how Robolux has changed the diaphragm valve as we know it.
Robolux provides a three-way diaphragm valve
A diaphragm valve is the only truly hygienic valve. There are other valves that are listed as being hygienic, which are used in breweries and dairies, but in the ultra-pure biotechnology and pharmaceutical industries they exclusively use diaphragm operated control valves.
This is because diaphragm valves are easy to drain; they’re two-way, so have two connections; there are no crevices inside; they provide a smooth flow through them; and you can polish the insides, so they’re very sterile.
The problem with a standard pneumatic diaphragm valve is that it’s just a single seat valve with an inlet, an outlet and an actuator on it. The diaphragm opens and closes to let flow through the valve. With a lot of valves used in industry, you can have a two-way valve and a three-way valve, so you have a third port inside the valve and the actuator closes one port and opens another.
You can’t do that with a traditional diaphragm valve because it’s only a two-way valve. Bürkert introduced the Robolux valve, which employs two pistons in one actuator to create a three-way type diaphragm valve.
Compact and lightweight 4-valve seat blocks
A conventional diaphragm control valve has a weir across the middle that seals the flow from one side to the other. The Robolux valve has two weirs and a gap in between the two, which is like a third port. The actuator allows you to open one weir, so the flow comes in and then goes out through the middle outlet.
You can close that weir and then open the other weir and get flow from the other way and that goes out of the outlets. Conversely, if you have flow coming up from the middle, you can divert it one way or the other. It then becomes a divert or mixing valve. There is no other pneumatic diaphragm control valve that can do that.
The beauty of the Robolux is that we’ve developed a way in which you can put an actuator on either side of the valve. If you take this valve with two weirs on one side and then machine the same on the other side you then have four valves in one small block with two actuators on it. A 4-valve seat block using a conventional pneumatic diaphragm valve is quite a big lump of stainless steel. We can get the same functionality with a much smaller lump of stainless steel.