Low water cutoff slow drain test - Section VI vs Section VII

[jeepy96]

Hey guys,

I have a question concerning the low water cutoff switch maintenance practices suggested in these two sections. We run 2 fire tubes boilers and one water tubes boilers.

Section VI - Care for Heating Boilers:

- Suggested that a slow drain test should be performed. (slow drain = draining the boiler level down to the low water cutoff switch set point (2’’ over tubes))

Section VII - Care for Power Boilers:

- Slow drain test aren’t suggested.

Q: Why are slow drain tests suggested for Heating Boilers and not Power Boilers?
Is there any risk associated to a slow drain test with Power Boilers?


Thank you
Have a nice day

 

[GenB]

Power boilers are more restrictive in control and protection of of low water conditions and are required to be blown daily.
Most heating boilers are not blown down daily, and their operation is passive: closed loop. By slowly draining the boiler prevents upsetting the steam release.

 

[cjw81]

Are these high (15 psig) pressure or low. Below 15 psig?

 

[jeepy96]

GenB - thank you for the information

cjw81- Heating Boilers < 15 psig
Power Boilers > 15 psig

 

[jmcx1969]

FWIW I had float type cut-off work fine on a quick blow test but fail on a slow drop. The magnet opposite the float that activated the micro-switch was too strong.

 

[littletoes]

Are we talking an Evaporative Test?

Doesn't code require these to be performed at least once a year?
LWFCO's shouldn't fail with a "slow" type of bleed down....think I'd be calling the manufacture if that became a problem.
Jmcx1969, what style/model LWCO were you using?