Valve opinions

Chris NJ_2

Question for the experts. This weekend I am replacing the shut off valves on the hot water coil, boiler water supply to the McDonnell Miller unit and the bypass to directly fill the boiler (with a backflow preventer). Should I use full port ball valves, gate valves or globe valves? Some of these like the hot water coil will be in the full open while others like the manual fill will be closed most of the time and only opened partially and occasionally. Your opinions?

Unknown

The full port ball valves

are definitely the way to go . But even the ball valves need some excercize - I had to shut the ball valve on my main last week and it was almost stuck in the open position . First time shutting it in 5 years or so . Other than that , you dont have to worry about a gate breaking off , or a rubber gasket failing , like in a globe valve .

J.C.A.

To add to Ron's ....

As you open and close them , they clean themselves . The only place I wouldn't use a ball valve would be a throttling situation . They tend to make moving fluid louder when partially open . Gates or globes for throttling . Chris.

Tony Conner

I Wouldn't...

...throttle with a gate valve either. You'll get a swirl up the back side of the gate, and it'll erode over time. Then, when you need it to hold, it won't. They do make a 'V' port ball valve for throttling, but it's special application, and pricy. I've only ever seen them used on actuated control valves. I've seen a ball valve on a little 1/2" copper cooling water line throttled. Granted, this was an application that was in service 24 hours a day, seven days a week, but after about 6 months, a hole developed in the copper line just downsteam of the valve. The throttling had increased the velocity of the water, directed it at one spot on the downstream line, and eroded it.

If you're gonna throttle, put in a globe valve. If you just need an isolation valve, then avoid globes, because the pressure drop is higher.

I don't get into the application that started this thread, but do full vs regular port ball valves make that much difference here? The length of the restriction is so short, that I'd think it would be hard to measure the increased pressure drop across a pair of regular port vs full port, unless the water was just singing through. In that case, I'd bet the flow would be exceeding the capacity of the coil to heat it anyway.

Jamie Hall

Not a steamfitter!

but I do a good bit of work in big water and wastewater systems... ball valves for shut off. No question. Simpler, more reliable than either gates or globes. But globes for throtting -- gates should, in my opinion (just me, guys) never be used for throttling -- all kinds of problems. Reduced port? Customary in the larger sizes -- as was said, the length is so short that the head loss is minimal, particularly if they are built right with an easy transition in and out.