What is a Control Top and What Does it Do?

Have you ever walked through an industrial fluid processing facility and seen a whole bunch of valves that appeared to be adorned with Christmas lights and wonder what those do? No, those are not what guides Santa’s sleigh to the end of the mayonnaise line, those are valve control tops. But what is a control top and what does it do? Let’s take a closer look.

A valve control top serves three main functions. First, it provides status of the valve- is the valve open or closed? Second, it provides an “action”- the ability to open or close the valve. Finally, a control top provides feedback- did the valve open or close as intended? In the control top are individual components that help accomplish each of these three functions. Now, let’s do a deeper dive on each of those.

From Left to Right- APV CU4 Control Top, WCB Control Top w/ SS Cover, WCB Control Top w/ Set & Forget Switch, WCB Control Top for W72 Mixproof Valve

Position Switches

For the first function- valve status or position indication- we use a switch. A switch in a valve control top detects a moving probe- usually a linear valve stem- and indicates valve change of state. The switch then sends a signal back to the main PLC to confirm the valve position.

There are a few different kinds of switches we see in Waukesha valve control tops, including microswitches, proximity switches, Hall Effect, and inductive sensors. We won’t go too deep on each kind of switch, just know that microswitches are a mechanical technology common in pasteurizer divert applications in Grade A dairies, while promixity switches are probably the most common type of switch detect a moving probe without making physical contact with the target, and inductive switches are used in newer “set and forget” applications. But ultimately, they all do the same thing- provide information about valve position.


The next function we have is “action”. Solenoids are what allows valves to actuate or change position. Solenoids are basically little electrical air check valves that control air flow into the valve actuator. Solenoids are typically provided in the “closed” state, meaning no air can flow through. When the valve coil is energized, however, a little plunger lifts, allowing air to flow forward into the valve actuator, causing the valve to open or change position. When the coil is de-energized, air supply to the actuator is stopped and the valve position returns to the closed or alternate position.

In Waukesha and APV control tops, solenoids are available in 110VAC and 24VDC versions. We should also mention that solenoids may not always be located in the valve control top. Occasionally, they can also be located in a remote panel, with poly flow or stainless air tubing routed the valve.


The final function our control top carries out is valve feedback or communication. Ultimately, the control top needs to tell the rest of the system what is going on in the valve. There are a number of ways to do this- ranging from a simple wired terminal strip, to an industrial communications card- such as ASi or DeviceNet- which can simplify the wiring, addressing, and communication of 100’s of valves. Again, we won’t get into the specific pro’s and con’s are DeviceNet or Profibus here, just know that one of the primary functions of the valve control top is to communicate with the rest of the system.

In sum, while valve control tops are often bright and provide visual indication of valve state, their three primary functions are to provide status of the valve, actuate or control the valve, and provide feedback to the rest of the system on the status of the valve. It accomplishes this with position switches, solenoid valves, and feedback cards. As always, if you have any questions about your valve control top or which is best for your application, contact a Triplex Sales Engineer today!

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