Some areas of confusion regarding the NFPA 85 standard
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5.3.6.4 Bypass 5.3.6.4.1 The interlocks on the low water cutouts shall be permitted to be bypassed only for blowdown purposes. 5.3.6.4.2 The bypass mechanism mentioned in 5.3.6.4.1 should be of a type that remains in place temporarily during blowdown. 5.3.6.4.3 The interlocks must not be bypassed manually at any time during normal operation. I would like to ask the experts here: what exactly does this text mean? What chain does it refer to?
The last edit to this post was made by xyc114 on 2015-9-8 at 11:23, and it discusses the role of bypassing in interlocking. Suppose an interlocked switch valve is placed alongside a manual valve; the manual valve serves as a bypass for the interlocked switch valve, and it remains closed in its normal state. It is the signal that controls the interlocked switch valve to determine its operating state. When the signal requires the interlocked switch valve to be closed, the medium can no longer flow. But for other reasons, some of the mass media need to be discharged, so only the manual valve can be opened. If there is no bypass manual valve, this issue cannot be resolved; a bypass manual valve must be added, and it can only be used for sewage discharge. It is not enabled under normal circumstances. Generally, a bypass is provided for maintenance purposes; repairing the main valve does not affect production.
Thank you. Also, what does low water cutout mean?
Low liquid level switch………………………………
I’m a bit confused about this. . Isn’t a level switch a transmitter? . What does it have to do with bypassing?
It’s not the switch transmitter at the liquid level; it’s the switch valve. Low water cutout: shutdown of water output at a low level; “cut out” means to shut off the flow of water.
Where is the position of this on/off valve?
As I understand it, the boiler low-level interlock can be disabled during blowdown, in order to prevent the low level during blowdown from triggering the boiler interlock. The low liquid level interlock must be activated during normal operation.