How to Fix a Flowswitch that Cycles?

10/8/2024

We have an instance of "flowswitch cycling" on a new wet-pipe system. The RPZ backflow is thought to be causing the flow switch to fluctuate and, therefore, not get us the flow alarm in a timely manner or at all.

We have opened the manual high point air vent and flowed for several minutes with no success.

Has anyone had this or found a solution to it?

Potter has a technical bulletin on this but does not go into detail about how to resolve it.

Thanks in advance.

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6 Comments

Dan Wilder

10/8/2024 06:47:19 am

Describe the system:
How many total systems downstream of the BFP
Grid/Tree
Multiple high points or areas of trapped water that feed back up to possible air pockets
Pipe sizes
Does the system use a lot of flex couplings?

One HPV may not be enough, may need a remote drain location to have additional flow points.

Glenn Berger

10/8/2024 08:15:14 am

In addition to Dan's response, I would add:

Is there temperature fluctuation to which the system(s) are exposed?

Have you tested the BFP to determined that it is in proper working order?

Derek Wallis

10/8/2024 08:27:19 am

We've delt with cycling flow switches in the past and it generally occurs on the tree type systems where air gets trapped at the end of the branchlines, compresses, then pushes back, causing the retard on the flow switch to reset. The way to fix a true cycling flow switch is by adding auto vent(s) or adding manual air vent lines at the end of the branchlines (similar to a dry system gang drain).

We recently installed a small 4" riser with an RP backflow and the cycling flow switch phenomenon was occurring. We added vents to get the air out and the problem continued to persist. We removed the check valves in the backflow and the switch stopped cycling and operated as intended. We reached out to the manufacture and found that they offered a "low flow" #1 and #2 check valve replacement. We ordered and installed the low flow checks, and the problem was solved.

GAFFER

10/8/2024 08:34:38 am

again, describe the system.

distance from RPZ to flow switch, as well as other valves?

distance from flow switch to insp test?

small riser room? floor controls?

Jack G

10/8/2024 10:22:36 am

Derek is on point. I ve found low incoming pressure to contribute the most. I use that to get the water company to allow the bfp to be on the discharge side of pumps.

Matthew Mueller

10/8/2024 10:59:07 am

Derick's point on the BFP causing issues as well. one manufacture in particular uses checks with a cam that won't allow full opening until a higher flow volume overcomes the "bump". Usually, one sprinkler flowing doesn't achieve what's necessary.

That said, trapped air is still the most likely cause.

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How to Fix a Flowswitch that Cycles?

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