Boiler Flow Switch - Safety Question

http://www.google.co.uk/search?hl=en&q=Boiler+and+Fired+Pressure+Vessel+Safety+Orders++ca+flow+switch&meta=

So... your saying your in hot water?

Ha! I love horrible jokes.

The boiler manufacturer. He had one installed or recommended it be there must be a reason. Ask them.

I am not sure of the regulations in California, but you may look to ASME BPVC Section VI - Recommended Rules for the Care and Operation of Heating Boilers.

This caused a lot of repercussions internally with the customer and now they are challenging us on whether or not it is a safety issue.

If it was installed there - this was one hell of a good Consultant who is aware of a pump failure safety measures. I am unaware of any code reference. Maybe someone else might refer. However, an additional safety irrespective, is worthwhile.

I am trying to imaging the situation you are put to!!!

So, during work, you, just by chance, found that a flow switch was disconnected (originally seemed to be connected at the beginning but now disconnected from the system).

Am I understanding your question correctly??? If then...

You mentioned it is a switch!! Then where the cabling was connected to??? (Sensing part was connected (now disconnected) to hot water system!!!)

Then you will come to know the function of this flow switch!!!

It may trigger standby BFW pump, or it may shut off fuel to boiler or it may have another function!!! It may have very minor function since your client did not have any technical problem while it is disconnected. (and they are challaging to you now!!!)

Check this out first, and you will now the function naturally~~~ of that switch.

Boiler suppliers usually specify a minimum flow, but I'm not aware of them wanting a flow switch, presumably to prove flow before fuel starts, and stop fuel if flow fails. At least not in domestic and smallish commercial situation - maybe on bigger jobs.

If the system has motorised valve(s) that can stop the boiler flow, the pump and boiler are energised via auxiliary contacts on the valve, which close when the valve is fully open.

If the pump fails the situation isn't as serious as a closed valve and I'd expect the boiler control-stat to come in before anything critical happens, maybe the limit-stat also if there's a lot of residual heat in the boiler.

Cheers.......Codey

Hi,

Flow switches are regularly used as part of a series of interlocks used to avoid operating the boiler under potentially hazardous conditions. These standards are to be found in the standards applicable in the cuntry of origin of the plant. Generally it is quite simply a case of good practise and something that any engieer worth his/her salt would automatically instal. ASME or even ASHRAE will give guidance.

Having been involved with high pressure hot water plant for many years I would never consider an application which did not have such a device in series with the burner firing controls. You may find the simple flow switch is not the ideal protective device and prefer to use an orifice plate with associeted delta P sensing as part of a flow metering device.

The obvious line-up of protection would include a pressure switch to indicate that the boiler was properly pressurised and also a high limit stat. Taken in concert with the flow sw you can then consider the installation capable of operating safely and within design parameters.