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boiler failure article in PME Mag, Mar 2004
bert waller
Member Posts: 4
Dear Dan,
The article was a good one, but left a couple of questions unanswered, and possible unsolved problems.
1. You said that boiler pressure increased when the radiator valves shut down. That implies that the boilers are connected to the pump discharge side. If the boilers were connected to the suction side, as they should be, there would be little pressure change at the boilers when the radiator valves close down. Repiping to put the boiler on the pump suction side might cost more than relief valve changeout, but would eliminate the problem at it's source. And would reduce other problems introduced by the higher pressures permitted.
2. The pump head of 80 ft seems to be excessive. This is a common cause of operating problems. The awkward design engineering that selected a snap-open bypass valve, and that placed the boilers on the pump discharge side also likely grossly oversized the pump head. That's common enough. I have "fixed" a number of systems by having oversized pump impellers shaved down. But I won't get started telling YOU war stories! You've been throught the mill!
Retrofitting a higher rated relief valve as you did, creates some possible new problems. Entrained air retained in the system will result in some corrosion in the boilers. Higher pressures allowed by the elevated relief valve will result in higher stresses on the new boilers. Corrosion and stress together make more trouble than the sum of both seperately, a condition well known to corrosion engineers. Those lightweight Hydrotherm castings have little reserve for corrosion. Let's pray for them.
Please keep writin' those good articles!
Regards,
Bert Waller
The article was a good one, but left a couple of questions unanswered, and possible unsolved problems.
1. You said that boiler pressure increased when the radiator valves shut down. That implies that the boilers are connected to the pump discharge side. If the boilers were connected to the suction side, as they should be, there would be little pressure change at the boilers when the radiator valves close down. Repiping to put the boiler on the pump suction side might cost more than relief valve changeout, but would eliminate the problem at it's source. And would reduce other problems introduced by the higher pressures permitted.
2. The pump head of 80 ft seems to be excessive. This is a common cause of operating problems. The awkward design engineering that selected a snap-open bypass valve, and that placed the boilers on the pump discharge side also likely grossly oversized the pump head. That's common enough. I have "fixed" a number of systems by having oversized pump impellers shaved down. But I won't get started telling YOU war stories! You've been throught the mill!
Retrofitting a higher rated relief valve as you did, creates some possible new problems. Entrained air retained in the system will result in some corrosion in the boilers. Higher pressures allowed by the elevated relief valve will result in higher stresses on the new boilers. Corrosion and stress together make more trouble than the sum of both seperately, a condition well known to corrosion engineers. Those lightweight Hydrotherm castings have little reserve for corrosion. Let's pray for them.
Please keep writin' those good articles!
Regards,
Bert Waller
0
Comments
-
> Dear Dan,
>
> The article was a good one, but left
> a couple of questions unanswered, and possible
> unsolved problems.
>
> 1. You said that boiler
> pressure increased when the radiator valves shut
> down. That implies that the boilers are
> connected to the pump discharge side. If the
> boilers were connected to the suction side, as
> they should be, there would be little pressure
> change at the boilers when the radiator valves
> close down. Repiping to put the boiler on the
> pump suction side might cost more than relief
> valve changeout, but would eliminate the problem
> at it's source. And would reduce other problems
> introduced by the higher pressures permitted.
> 2. The pump head of 80 ft seems to be excessive.
> This is a common cause of operating problems.
> The awkward design engineering that selected a
> snap-open bypass valve, and that placed the
> boilers on the pump discharge side also likely
> grossly oversized the pump head. That's common
> enough. I have "fixed" a number of systems by
> having oversized pump impellers shaved down. But
> I won't get started telling YOU war stories!
> You've been throught the mill!
>
> Retrofitting a
> higher rated relief valve as you did, creates
> some possible new problems. Entrained air
> retained in the system will result in some
> corrosion in the boilers. Higher pressures
> allowed by the elevated relief valve will result
> in higher stresses on the new boilers. Corrosion
> and stress together make more trouble than the
> sum of both seperately, a condition well known to
> corrosion engineers. Those lightweight
> Hydrotherm castings have little reserve for
> corrosion. Let's pray for them.
>
> Please keep
> writin' those good articles!
>
> Regards, Bert
> Waller
Retired and loving it.0 -
> Dear Dan,
>
> The article was a good one, but left
> a couple of questions unanswered, and possible
> unsolved problems.
>
> 1. You said that boiler
> pressure increased when the radiator valves shut
> down. That implies that the boilers are
> connected to the pump discharge side. If the
> boilers were connected to the suction side, as
> they should be, there would be little pressure
> change at the boilers when the radiator valves
> close down. Repiping to put the boiler on the
> pump suction side might cost more than relief
> valve changeout, but would eliminate the problem
> at it's source. And would reduce other problems
> introduced by the higher pressures permitted.
> 2. The pump head of 80 ft seems to be excessive.
> This is a common cause of operating problems.
> The awkward design engineering that selected a
> snap-open bypass valve, and that placed the
> boilers on the pump discharge side also likely
> grossly oversized the pump head. That's common
> enough. I have "fixed" a number of systems by
> having oversized pump impellers shaved down. But
> I won't get started telling YOU war stories!
> You've been throught the mill!
>
> Retrofitting a
> higher rated relief valve as you did, creates
> some possible new problems. Entrained air
> retained in the system will result in some
> corrosion in the boilers. Higher pressures
> allowed by the elevated relief valve will result
> in higher stresses on the new boilers. Corrosion
> and stress together make more trouble than the
> sum of both seperately, a condition well known to
> corrosion engineers. Those lightweight
> Hydrotherm castings have little reserve for
> corrosion. Let's pray for them.
>
> Please keep
> writin' those good articles!
>
> Regards, Bert
> Waller
Retired and loving it.0 -
The human side of that one, Burt,
was that no one wanted to take the blame for anything. My guy was there as a service contractor and he was just curious as to what had happened. When we spotted what we did, no one would believe us (people are fascinating). I suggested the higher-pressure relief valves as the lowest-cost solution and that's what the service contractor installed. He died a year or so afterwards and I never did hear what had happened down the road.
Thanks for the feedback, and the kind words.Retired and loving it.0
This discussion has been closed.
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