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"local" Transients

"local" Transients

(OP)
I work at a water utility and we have had some customer complaints about noisy pipes. We have done the standard checks, which include inspecting the meter and double checks at their service connection and making sure all line valves are fully open. We also advised them of the possibility of air in their lines or a faulty Pressure Reducing Valve. They claim to have had their system checked by a plumber and everything is supposedly working properly.

In order to go a step beyond the basic checks, I installed a new logger that we are trying by Telog which can monitor for transients and capture impulse data. I attached the logger to a hydrant at the end of their street and got the reading attached to this post. There have been a few instances of this occurrence and one matched up (time wise) to the complaint of pipe noise. This appears to be a local issue, meaning the source is not due to our operations or hydrant testing, etc.

Talking to others internally, there was at least one case where a customers faulty ice maker was causing similar issues for adjacent customers. I found it hard to believe that plumbing issues with one house could be transferred to neighbors, but this might be one of those cases. Does anyone have a similar experience who can offer advice which I can pass on to the customer on how to resolve?

Thanks in advance!

RE: "local" Transients

I too work at a water utility, and have investigated many similar complaints. (The Telog hydrant recorders are perfect for this purpose, as long as it's not freezing weather. We have 10 of them.) I was able to trace almost all cases of this type of complaint to our operations, particularly pump shut down, sometimes miles away. It seems that some pipe configurations, either in the street or in the customer's plumbing, may be resonant with the disturbance. I would encourage you to investigate all pump and regulator operations that might affect the zone this customer is in. Next to our operations, I suspect the customer's own plumbing - more than once I installed recorders on the customer's plumbing and on an exterior hydrant to establish the problem originated with the customer's plumbing. I have seen faulty household PRVs causing this, as well as just plain loose pipe hangers. I have never found a case of one customer's use causing this problem at a neighboring customer. Good luck, and please keep us posted with what you find out.

RE: "local" Transients

(OP)
I'm sure its not due to pump shutdowns because this zone is fed strictly from reservoirs. We pump up to large ground storage tanks and it gravity feeds down through the system which we can do due to the topography. The only possible thing, operations wise, would be the closing of an altitude valve on one downstream reservoir, but its only closed twice in the past month and not around the time of the disturbances.

We have also not been exercising valves at these times and its outside of times where the FD would do hydrant tests. I'm at a loss. Maybe I'll look closer at valve operation at the upstream reservoirs and see if something jumps out.

When you installed a recorder on the customers plumbing and then on the hydrant, do you see the disturbance at the hydrant or does the PRV keep the issue within the residence? In other words, does the PRV (or possibly backflow preventer) create a barrier for transients? We only have one logger, but plan to get more. As a side topic, what other ways have you used them to solve real world issues? I'd love ideas on how to maximize the technology.

Thanks for the feedback!

RE: "local" Transients

Obviously I don't know your system configuration. But unless the pump and pipe to the tank has nothing in common with the distribution system, including tank inlet/outlet, I wouldn't discount the effect of pump operations on system transients, even when there are tanks feeding the area by gravity.

In my experience, transients are too fast to be effectively filtered by PRVs. A transient in the main passes right through a customer's PRV.

On the other hand, I haven't found any customer caused transients causing problems in the main. In only one instance of interior/exterior monitoring has the exterior recorder even shown a blip corresponding to the interior transient. And that was small enough that I'm sure no other customers could have noticed. I attribute that to the magnitude of the customer's transient.

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