A Little Isolation Can Be a Good Thing in Fluid Systems

Block and bleed valves provide a margin of safety for maintenance and repairs

Think about the last time you checked the air in your tires. When you popped the gauge off the valve stem, what happened? Right: A puff of air came out.

When it's plain old air with only about 35 pounds of pressure behind it, that brief burst is no big deal. When it's anhydrous ammonia or a refined petroleum product with high pressure behind it, a brief burst can bring serious injury, or at least an unwanted spill.  

That's why isolation valves are a crucial part of many industrial fluid systems. As the name implies, an isolation valve allows you to safely isolate a pressure gauge, regulator or other component when you have to replace it or perform maintenance. One type of Isolation valve is known as a block and bleed valve. The name is a good description of how they do their job. One handle lets you close the valve and block any process fluid from entering. A second handle allows you to bleed off the remaining pressurized fluid to drain to the atmosphere or to an approved collection device. A double block and bleed valve provides two isolation points, with the bleed valve between them.

Block and bleed and double block and bleed valves also give you an isolatable access point. They make it easier to calibrate a device on the line, or add a fluid. For instance, the valves can make it easier to add glycol to a gauge, or add nitrogen to a system.

Education gap

A surprising number of people don't realize they need to bleed the line, says Sam Johnson, oil and gas market manager for Swagelok. "I've seen many a time where you go into an older refinery and the gauges just have a single globe or gate or needle or ball valve," he says. Even if they understand that they need a block and bleed combination, many people don't really understand why. They use a single block valve because the specs call for it, and they don't think about it. Often these are people who have acquired the the proper education that they need, but haven't had many years on the job.

"They know the basics, but when it comes to system layout they typically are going to adopt whatever they see in the first couple of years after school, both good and bad," Johnson says. If they have been working with a fluid that's safe, the system may have gotten by with just a block valve. It's easy, then, to say "We did it this way at my old plant and it worked very well." 

"Having the bleed valve is a very easy way to guarantee the system is depressurized downstream of the valve when you are removing a gauge or other device," Johnson says.

Help the helper

When it's time to call Edmonton Valve & Fitting to talk about isolation valves, a bit of homework will make the conversation go more smoothly. We like to use the acronym S.T.A.M.P.E.D., which stands for Size, Temperature, Application, Media, Pressure, End Connection, and Delivery, just like we use for hoses. Gather that information about your fluid system and it will be easier to find the specific model of isolation valve that you need.

With isolation valves in place, your system will run safer and cleaner.

"To me a block and bleed valve is cheap insurance," Johnson says. "With Block and Bleed type isolation valves, your system will run safer and cleaner - and you won’t end up with an unwanted chemical release, or worse, system fluid sprayed all over you.