Safety Valve 102

Earlier this year, I shared a little product education on safety valves that can make you look really smart to customers, which usually means more orders for everything you sell.

Well, class is back in session and here comes the judge. I guess I am showing my age.

Adding a bellows to a valve

We talked last time about direct acting safety valves. The plain-Jane type. Today I’m going to talk about what happens when you add a bellows to the valve.

These are the kind of valves used by refineries, petrochemical plants, natural gas plants and the like where there is a process. To sell to these folks, you need to ask as many questions as possible.
• Is the outlet piped away or vented to the atmosphere?
• If it’s piped away, is it a straight run or is it going up to a tank?
• Ask for a spec sheet with the makeup of the fluid, relieving temperature, viscosity, set pressure, required flow rate, and if there is any back pressure.
• Is the back-pressure constant or variable?
• If the back pressure is constant, how much do you have?

A safety valve is two pieces of metal pushed together by a force. Normally this force is the spring pushing down on the disc but if there is constant back pressure, that pressure also comes back on the disc from the outlet process. If the valve is to be set at 100 psig and constant back pressure is 15 psig, then we set the valve at 85 psig and indicate on the nameplate that there is 15 psig of back pressure.

Know how the piping is arranged

Knowing how the piping is arranged is important because there may be variable back pressure. For example, if the safety valve is protecting a pump and the outlet piping goes up 25 feet to a tank, when the relief valve goes off most of the fluid will dump into the tank. However, not all of it will make it and will come back on the safety valve.

In this case, the back pressure might be 10 psig most of the time but it is possible that it will vary up to 25 psig or 50 psig. The variation is created because of the varying level of product in the tank. If the tank is low, most of the fluid will be captured in the tank. But if the tank is three-quarters full, a lot more of the product coming back on the safety valve with more force than usual.

How to deal with back pressure

To deal with variable back pressure, a bellows is put inside of the valve. It works so well there is no compensation when you set the valve. So, if the valve is set at 200 and you have 50 psig of variable back pressure, you set the valve at 200 because the bellows negates the back pressure. If you didn’t put a bellows in and you set it at 200, then it would go off at different pressures because of the variable back pressure.
The bellows also isolates the top part of the valve from the bottom part. If the product is corrosive, only stainless steel can come into contact with it. By putting a bellows in the valve, your customer can buy a half stainless valve and save some money because the bellows will prevent the product from getting up into the spring housing.

Know what is going through a safety valve

It is important to always find out what is going through a safety valve. If it is a light gas, such as hydrogen or helium, then an O-ring disc is required to prevent leaks. Anhydrous ammonia in gas form is another problem child that needs a soft seat. If the process is a slurry, an O-ring will help avoid extra problems.

One more thing: It is good to know if the safety valve is mounted on top of a rupture disc. A rupture disc will cut down on the flow rate of the safety valve. Knowing there is a rupture disc will help size the proper valve. A rupture disc holds tighter than a safety valve but if it goes off, there is no protection until they can shut down to replace the disc. That is why many times a safety valve is put on top of the rupture disc.

Well, class, that’s enough for today. There won’t be any pop quizzes on this material. Just more orders and money in your pocket because customers like buying from smart people.

We know you have a choice where you buy your safety valves. You might leave us for a while, but we are pretty damn good at what we do, and we’ll be happy to see you when you come back. I might curse at you under my breath for listening to someone else and being lured to the dark side, but we will always welcome you home.

Stay healthy and happy, and please come by to see our new facilities. They are second to none, and you can even look at our beautiful new Consolidated 2700 series, 1700 series for high pressure boilers and P1 trim valves for economizers.

NASVI Welcomes New Sales Team Member

Christina Sloss, one of North American Safety Valve’s new application engineers, is also new to Kansas City. She and her boyfriend took a leap of faith and moved across the country from Houston, Texas, for a promotion he accepted with his company. She’s grateful to have found North American Safety Valve just a month after moving to town. “There is never a dull moment here, whether it is sizing valves for rush orders or someone singing down the hall,” she says. “It’s just another day in paradise.”

No stranger to new cities, Christina received her B.S. degree in Agricultural Science from the University of Hawaii. Leaving Hawaii after six years in paradise was a tough decision, but she is glad she was able to spend priceless time with her big extended family in Houston. In fact, it was working in the family trade that she gained six years of experience selling instrumentation valves and fittings, leading her to a rewarding career.

When Christina isn’t at work, you can find her digging in her vegetable garden, learning about native plants or pruning fruit trees. She is an avid gardener and environmental advocate. She said, “I am thoroughly enjoying getting to know Kansas City and laying down new roots.”

Contact our sales team at (800) 800-8882 or and give us a chance to go on the hunt for the valves you need

View More Articles