Gate or ball valve

152NP

Can someone recommend an economical 4 inch gate or ball valve to be used on steam risers. This is for a low pressure two pipe system. I have a situation where I will have two boilers, burning different fuels,  sharing a common header. I wish to isolate whichever boiler is not in operation.

Brad White

Steam-Rated Ball Valves

A 4-inch OS&Y (Outside Screw and Yoke) gate valve is a traditional approach and is a thing of beauty. They are also much larger, heavier and take up more space than a ball valve. The screw moves in and out when the valve is closed or open as a visual indicator. They also tend to cost more.



For these, we specify Milwaukee, Jenkins Bros. for commercial work or AVK or Kerotest for high end work. Any valve corresponding to MSS Class 125 or better yet, 150, for low pressure steam, will serve well. The 150 class gets you a better valve quality and trim. Cost it out.



For ball valves, we pretty much settled on Neles-Jamesbury for steam work. There are others but no equals. In public work we specify gate valves only for this reason and Neles-Jamesbury for private work where we do not have to name three names.

EDIT: Spirax-Sarco also makes the cut.



EDIT: As Jamie pointed out below, FULL PORT ball valves only.

I would also add, R-PTFE (fiberglass reinforced Teflon) as a seat material with others using some proprietary materials, such as PEEK).



My $0.02



Brad

jpf321

my $0.02

Brad seems to have laid it out clearly but I wanted to add that I just purchased an "import" gate 3" threaded. It was very economical, I'm residential and it will be used as my king valve to build pressure for an occasional high-pressure (4-5psi) blowdown and normally open. I don't intend for it to see a great deal of operational service so I went cheap.



It was recommended to me to NOT go the ball valve route since the teflon seals may tend to degrade. Although I know there are steam rated ball valves out there, I went the cheap yet seemingly more safe route with my cheap gate.



I had looked at GATE: http://www.simplyplumbing.com/milwaukeevalve-1057.html

AND BALL: http://www.pexsupply.com/Matco-Norca-750T10-3-Full-Port-Threaded-Ball-Valve-4235000-p

My gate ended up being about the same price as the BALL linked above.

Brad White

Blow Me Down!

I probably should have been more explicit but at some risk of general vs. specific advice. To be steam rated, on ball valves, we require RTFE or reinforced Teflon for the seats. Remember, Teflon can take 500 degrees.



For a blowdown situation, ball valves are superior. A gate valve opens slowly enough, (unless lever operated and I *know* you are not using one). So when slowly turned, your pressure surprise is gone.  But I also suspect as your king valve, you are just denying the system and blowing down the bottom, so wanted to make that clear for a wider audience. Still, if using it as a king valve, quick opening is a key component.



Now, I do have to question the "blowdown" procedure. Obviously not over 15 psi because of the relief valve but a small volume boiler can get there very fast. I have seen this done only on high pressure boilers, but under normal conditions, not on a low pressure home heating boiler. I just want to clarify that before someone gets the idea that this is something they should try.

jpf321

right..

i operate at sub-1psi .. so high pressure to me is more like 4-5psi :-)



thanks for the clarity on the RTFE ball valves .. was not aware of that option.



i'm a little confused by why as a king valve quick opening would be beneficial since it's really just an isolation valve during this bottom blow procedure.



FYI: I editted my post above to make my high-pressure mark clear.

Brad White

King Valve

The quick action on the valve is more for release of pressure, more rapidly than shutting down the burner, that was all.

Jamie Hall

And I will chime in with my usual caveat...

Whichever kind of valve you are using, be sure -- very sure -- that it is a full port valve (that is, for example, on a 4" ID line, the opening through the valve is 4" also).  The temptation is to get a reduced port valve, as they are a lot cheaper.  Don't.  You might get lucky and your particular setup might work.  Usually, though, with the low pressure saturated steam we are looking at, you will get a good deal of condensation going through the reduced port, and remarkably little steam getting by...

Jean-David Beyer

you will get a good deal of condensation going through the reduced port

The guys I know who run steam railroad locomotives have to blow down the boiler rather frequently. These are relatively small locomotives that run at 150 to 175 psi. I am not quite sure what kind of valves they have, surely not ball valves. When they open the valve, I would have expected them to get a huge jet of superheated water, but they do not.  They just get steam that rapidly condenses into a cloud of water vapor. You do not want to get in the way of that.

Brad White

Thanks, Jamie!

You are correct, Sir. That is no caveat, but good practice and the fine line between brevity and thoroughness deserves your words. Full port is also our standard for any ball valve, with few exceptions, but it should have been said.



Thanks



Brad

152NP

Still trying to figure out the best solution

Thanks for your input. It was interesting to see the sudden price jump when going from 3" to 4" on the gate valves jpf321 recommended. Wow! My situation may prove to be more tricky on the oil fired boiler. There is very little piping between it and the header. It was suggested to me by an old timer that butt weld valves might be the way to go. I doubt I could fit unions or flanges into what I have to work with. I haven't been able to find prices on the web for such a valve. I need to make some calls. Is there a concise source for information concerning all the ASME and MSS valve classes? I haven't been able to find anything on the web that is not a mess of crossreferences. I confessedly don't know much about the rating systems but would like to learn.