ASME CSD-1 and probe style LWCO
ASME CSD-1 and probe style LWCO
(OP)
Anyone out there run into this before or offer their thoughts:
I designed a central steam boiler plant for a hospital - 150 psig relief valves. The boiler water level LWCO safeties are Warrick probe style conductivity sensors. Facility experiences frequent power bumps in incoming grid electricity, which cause the probe style LWCO's to trip. Since LWCO#2 (the lower one) is a manual reset as called for by code the brief interruption of power locks out the boiler until an operator can come in and do a hard reset. While it is recommended to have 24 hour supervision for this class of plant, it is not required by our state and thus the plant engineers only are on site two shifts during the week, less on weekends. Brief power outages knocking out steam plant is causing major grief.
ASME CSD-1 section CW110 (under general requirements for water level control for all boilers) state: "Probe type LWCO's- An open circuit failure, break or disconnect of electrical circuit causes shut down of the fuel supply".
In looking up the LWCO's that we have, Warrick model 26, http://www.gemssensors.com/~/media/GemsNA/CatalogP... I see that the model 26 is CSD-1 compliant and UL 353 listed. There is an optional feature for preventing nuisance trips due to power outages. Looks like just the ticket. Boiler mfr. however says changing to this option model will be non-compliant and will void warranty. I am going to call Warrick in the morning to see if the optional device is compliant, but I am looking for advice / input on this situation.
I designed a central steam boiler plant for a hospital - 150 psig relief valves. The boiler water level LWCO safeties are Warrick probe style conductivity sensors. Facility experiences frequent power bumps in incoming grid electricity, which cause the probe style LWCO's to trip. Since LWCO#2 (the lower one) is a manual reset as called for by code the brief interruption of power locks out the boiler until an operator can come in and do a hard reset. While it is recommended to have 24 hour supervision for this class of plant, it is not required by our state and thus the plant engineers only are on site two shifts during the week, less on weekends. Brief power outages knocking out steam plant is causing major grief.
ASME CSD-1 section CW110 (under general requirements for water level control for all boilers) state: "Probe type LWCO's- An open circuit failure, break or disconnect of electrical circuit causes shut down of the fuel supply".
In looking up the LWCO's that we have, Warrick model 26, http://www.gemssensors.com/~/media/GemsNA/CatalogP... I see that the model 26 is CSD-1 compliant and UL 353 listed. There is an optional feature for preventing nuisance trips due to power outages. Looks like just the ticket. Boiler mfr. however says changing to this option model will be non-compliant and will void warranty. I am going to call Warrick in the morning to see if the optional device is compliant, but I am looking for advice / input on this situation.





RE: ASME CSD-1 and probe style LWCO
RE: ASME CSD-1 and probe style LWCO
Most such controls are run from redundant power, in effect an industrial battery backup. Such systems are available, and depending on your need can be configued for redundant backup.
Short of lossing power for all prime movers, you want the emergence controls to remain powered otherwise you are flying blind.
You will also need emergency lighting.
Having said all that, most modern hospitals in have emergency power backup to avoid a complete blackout.
RE: ASME CSD-1 and probe style LWCO
That is exactly what I need. However blr mfr says this is not code compliant - would be for section IV boilers but not for section I. I think it may come down to interpretation of CSD-1, and how they treat probe style LWCO. Regardless, if the OEM mfr says is it not compliant, I probably need a different solution. May need to switch to a mechanical float, where switch only breaks when water is low, not when water is low or power goes out.
RE: ASME CSD-1 and probe style LWCO
General Blr. CA,USA
RE: ASME CSD-1 and probe style LWCO
Does ASME pressure vessel code talk about water level controls? I have read through CSD-1 and have found the following: Under section CG-610 LOCKOUT: "Safety controls that can electronically reset without local manual intervention, such as when power or control input to the device is interrupted and then restored, shall not be permitted." To me this is expressly denying the Power Outage optional feature of the Warrick 26 (or other conductivity style LWCO). I am thinking the thing to do is go simple and swap the Warrick 26 manual reset LWCO to a float style such as the McDonnell Miller 93. It simply avoids the issue altogether - as the switch breaks only when water level is actually low, not when water is low or when power is lost.
RE: ASME CSD-1 and probe style LWCO
General Blr. CA,USA
RE: ASME CSD-1 and probe style LWCO
RE: ASME CSD-1 and probe style LWCO
General Blr. CA,USA