Comprehensive Control Valve Repair: What It Is and Why You Need It

A faulty control valve can cause major problems in your plant. For example, it’s not unusual for companies to lose upwards of $1 million per year because they can’t maintain the correct steam pressure in a line. If operations have to shut down entirely, losses can be to the tune of $20 million per day.

Obviously, you’d like to prevent control valve problems. And when they do happen, you’d like to fix them and get your plant back up and running as soon as possible.

The best way to do this is by looking at the bigger picture of control valve repair.

No valve is an island

A control valve doesn’t act on its own. It’s part of a larger valve assembly that also includes an actuator and a positioner, and sometimes other elements like regulators and limit switches.

This assembly is itself part of a larger control loop that includes sensors to measure the process control variables (flow, temperature, pressure, etc.) and a controller to tell the valve assembly how to maintain the desired variable levels.

And, of course, the control loop is just one of many, all of which operate in the context of the larger plant systems.

It’s important to understand all of the components of a control loop because, if the valve stops working, any of these components may be at fault. Often, it’s a combination of problems.

Here’s a real example one of our technicians encountered:

The problem

A power plant used attemperator spray valves to maintain a constant temperature in a steam turbine. Only a very small control signal should have been required — 0.25% to 0.5%. But even when the signal changed 5%, the valves didn’t move.

The causes

The technician found three problems: the packing was failing, the positioners were worn out, and rust from the plant piping had contaminated the valves’ internal parts.

The solution

During a three-week plant outage, the technician rebuilt the valves and replaced the positioners.

 

It’s also common for our technicians to be called about a faulty actuator, but then discover it’s a problem with the valve. In fact, about seven out of ten times an actuator fails, the underlying issue isn’t the actuator at all. For example, the valve stem may be worn out, the packing may have seized up, or there may be some kind of obstruction in the system.

Another problem we see frequently is incorrect positioner calibration, which can cause a control valve to leak or stick.

What this points to is that all of the components of a control valve assembly function as a single unit.

That’s why we recommend comprehensive control valve repair using a diagnostic tool like ValScope.

ValScope allows the technician to identify exactly what’s wrong with a valve — and potentially any other part of the control system — without having to pull the valve out of the line and take it apart.

ValScope reduces downtime because the testing can be done in situ and, if the line does need to be shut down, the technician will know exactly what repair work needs to be done. It also saves you money by allowing you to fine-tune your maintenance schedules based on valve performance. This boosts efficiency across your entire operations.

Don’t waste time and money repairing the wrong things. Contact us to learn more about our comprehensive control valve repair services.

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