Wiel McLean Model 88 series 2 installation

[tbedford]

I have two new low pressure steam (steam pressure set to 8 psig) boilers operating in parallel. These boiler have independent piping leading to separate pressure reducing valves. The valves are set to system pressure of 5 psig. Downstream of the PRV's is a steam header and off the header the steam travels to various zones.

Intermittently, after a burner shuts down, we have noticed that the steam pressure continues to build in boiler #2. It has opened the high pressure safety limit (set to 13 psig) several times. This results in a nuisance trip and alarms our local idiot light.
Boiler #1 does not exhibit this problem.

We have investigated the burner control and it is shutting off the gas valve when it should. Both burners have independent control systems. Where do we get the extra prssure from??

Any ideas,
Thank you,
Tom

 

[pmover]

how old are the boilers? how is the water quality? are the safety devices inspected yearly (i.e. removed, inspected, cleaned, etc.)?

as strange as it may seem, but if the water quality is poor, the solids can/may collect and adhere to the cast iron section walls. thus, the solid matter is still hot enough to generate steam once the fuel is shutoff. eventually, the cast iron sections will crack due to excessive heat (poor heat transfer). then again, i've seen cracked cast iron sections filled with scale and not leak. if the boiler is cleaned regularly &/or has excellent water quality, then this is likely not the problem.

are you sure the PRV (pressure reducing valve?) is working properly?

is the pressure relief valve (safety) connection clean and free of solid matter?

hope this helps.
-pmover

 

[tbedford]

thanks, pmover

the boilers are new 2.5 MBTU replacing older boilers
and the issue has been happening since start-up last spring..
all other accessories are new,
water quality is within specs,
thx,

 

[EdStainless]

Is the boiler shutting down because of reduced demand?
I suspect that the tuning constants for the two boiler controllers are different.
Leading boiler #2 to shut off too late and resulting in the overshoot condition.
Look at the controls.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube