Interesting steam main, pressure relief/bypass setup.

JohnNY

Midrise building in upper Manhattan. Every branch of the main is set up this way: A gate valve with a pressure relief valve piped back into the system. I've seen similar arrangements immediately off a 12" header but never on branches like this.
Have you ever seen a unique piping arrangement that made you wonder what happened to motivate such an installation?

SlamDunk

Interesting. Is gate valve always closed (bleeder valve) and the left side vented thru roof? Otherwise, if valve is open, then pressure is equal on both side of valve. Can't see much relief happening.

Jamie Hall

Love to know the logic on that one. A similar arrangement is common on large water mains -- only the bypass also has a valve on it -- to equalize pressure on the two sides when trying to open the main gate (otherwise it will be immovable!) -- but???

JohnNY

The theory seems to be that closing the gate valve makes the system much smaller, and in the absence of a modulating burner on this Scotch marine boiler, is likely to result in a faster pressure rise at the boiler side of the valve. I guess in a runaway condition the relief valves will open and deliver excess pressure to the system side of the gate. I’m here because the gates don’t hold well enough and they’d like to swap them out for ball valves. It seems they use them frequently, which of course raises its own questions, but I’m considering the (lack of) wisdom of not returning the relief valves to the installation. 

This is one of those things that seems so odd that I’m clearly either missing something or what’s here is just wrong. By the way, the relief valves are rated to activate at 30 PSI, so what the heck are they ever doing anyway? Boiler runs at 2-3 PSI and I’ll deal with that later. 

Of course the boiler is also fitted with a 2” relief 15 PSI relief valve. 

SlamDunk

So, they close that valve often and the boiler becomes oversized because there is only one firing rate. Over pressure causes relief valve to open and send excess to emitters that are not needed (isolated by gate valve). I get it. Very creative.

JohnNY

SlamDunk said:

I get it. Very creative.

Right. I haven’t made up my mind yet if I admire it or hate it. 

mattmia2

Are you sure they have the spring in them that they say they have? What sense would it make if the boiler relief valve is 15 psi and they are 30 psi unless someone changed the spring to make them say 10 psi.

SlamDunk

I like it. It doesn't waste water. Probably momentary relief. Kinda energy efficient.

Alan (California Radiant) Forbes

Does it have anything to do with the boiler being oversized? And I get confused with the use of "relief" valve. Wouldn't that be a bypass valve?

EdTheHeaterMan

JohnNY said:

I’m here because the gates don’t hold well enough and they’d like to swap them out for ball valves. It seems they use them frequently, which of course raises its own questions, but I’m considering the (lack of) wisdom of not returning the relief valves to the installation. 

This is one of those things that seems so odd that I’m clearly either missing something or what’s here is just wrong. . 

Is the building super sure it ts the gate valves that are not holding very well? Are you sure those bypass relief valves are not bypassing? Maybe a test of the bypass relief valves are in order. Remove the union and cap off the downstream side of the smaller bypass pipe and see if the relief valve holds.

egansen

I don't know the why but that arrangement would make me nervous.   Say you have the valve closed and you are working on something downstream of the valve.  If the relief/bypass valve opens you could get hit with steam and injured. 

Steamhead

Maybe the system used to run at higher pressure? This would explain the 30-PSI safety valves on the bypasses.............

JohnNY

EdTheHeaterMan said:

Is the building super sure it ts the gate valves that are not holding very well? Are you sure those bypass relief valves are not bypassing? Maybe a test of the bypass relief valves are in order. Remove the union and cap off the downstream side of the smaller bypass pipe and see if the relief valve holds.

I think his hands aren't working the way they used to and he just wants ball valves instead of having to turn the gate valve handles.

He's asked me to remove the pressure relief/bypass valves entirely and I thought I might give it a think before agreeing to do that, and so here I am, crowdsourcing for opinions.

Jamie Hall

If that thing in the red square, @JohnNY , is a valve in the pipe which closes off the bypass, then I think I may understand. No guarantee. A gate valve can be remarkably hard to open if it is closed against a pressure differential. I wouldn't have thought those were big enough to be a problem -- not the pressure differential great enough -- but who knows. In any event, if that thingy really is a valve, when the downstream is off and you want to turn it on, open that little bypass valve and let the pressure equalise. Open the gate valve. Close the bypass. Then when you want to close the gate, open the bypass again, close the gate, and then close the bypass.

That's what we do on big water mains. Wouldn't have thought it was necessary here, but who knows?

SlamDunk

I would give him the quarter turn valve because I feel his pain and leave the bypass installed just because it is a neat idea and doesn't present a danger.

Why engineer something out when it does its job? You will re-create the original problem that required its installation.

ChrisJ

SlamDunk said:

I would give him the quarter turn valve because I feel his pain and leave the bypass installed just because it is a neat idea and doesn't present a danger.

Why engineer something out when it does its job? You will re-create the original problem that required its installation.

30 PSI reliefs on a 15 PSI max system?

I don't see them doing much of anything other than getting stuck shut.

SlamDunk

Those things don't get stuck closed in my experience, they are above water. Leak, or stuck open, on the other hand-all the time with high usage. They weren't designed to be regulators. Emergency use only.

If 30 psi is an issue, then install a lower rated relief valve. It would make sense, except they weren't design to regulate. But, from the layer of dust and a lack of wrench marks, it doesn't look like anything has been replaced on blue pipe. Looks original. Who knows?

JohnNY

SlamDunk said:

leave the bypass installed just because it is a neat idea and doesn't present a danger.

Why engineer something out when it does its job? You will re-create the original problem that required its installation.

Normally I'd agree with you but look at the lengths of those nipples on the blue piping. I don't think I'll fit a ball valve in that space.

mattmia2

Isn't there an extension shaft accessory for the ball valve handle that would get it out past that bypass?

DanHolohan

I've been thinking about this for a couple days and can't come up with any reason why that relief valve should be there.

EBEBRATT-Ed

@JohnNY

with a 15 psi relief on the boiler those valves do nothing remove them and collect the scrap money

maybe at one time they were on higher pressure district steam as @Steamhead alluded to.

actually what you need is flanged ball valves that will bolt righ in in place of the gates.   Apollo and others make them$$$$$

I would also put a 1” ball valve in as a bypass

this can be used as a warm up valve and will keep the $$$ big valve from excess ware 

gennady

I think this valve is adjustable. There should be an adjustment screw under the cap, to adjust the pressure setting, so the pressure relief valve opens only when the steam pressure reaches a certain preset pressure. Probably they wanted to set some kind of priority zoning and delay steam delivery to the non-priority zones. What makes me wonder, is what happens with the condensate in this arrangement.
Reminds me of when half of the roof of the energy power plant I was working on was blown away together with the 24" relief valve discharge piping after the welder decided to weld closed drip from that discharge piping because condensate was dripping on the floor. The condensate filled discharge pipe, and when relief valve opened up, releasing 3800 PSI overheated steam, the flight had happened.

retiredguy

I have thought about this system since it was first posted and have come up with a couple far out ideas. Since I worked on systems in buildings similar to this I put on my "way out idea" cap. Start with that relief valve set at a very low pressure. #1); could this be someones idea of a type of freeze stat to keep certain pieces of radiation or fan coils from freezing in very cold weather. The bypass sends a small amount of steam out when the main valve is closed. #2); could this be a way to reduce the condensate load when the large valve is opened after being closed for an extended period of time. It would keep the piping warm to reduce the condensate load. #3); It was how they warmed up the piping slowly after a long boiler shutdown, say in the spring time when the boiler is fired once or twice in the morning only. #4); They had a "nut case" of an engineer that had nothing better to do than prepare for a non-event.