Pilko, yes I read them and like the idea. Each suggested method will work, just a matter of what will work best for the original poster. Since this setup is in place and working, less any flow detection my guess is freezing is not an issue. Most of my efforts along these lines were industrial applications, things like cooling lines for big pumps so I tend to gravitate to things like flow switches. The problem with my thinking is while fine for an industrial application a good flow switch and timer may not be in the original poster's budget. I haven't a clue what the budget is. Anyway, yes, I liked what you proposed as a good solution.

Ron

 

Wayneh:

There are better options, in my opinion. The one used in my water softener is a little rotating "propeller" with an embedded magnet. A hall sensor detects the rotating magnet. I bring this up because it's probably the cheapest way to measure flow. If it wasn't, they'd switch to something else to cheapen it still more.

A piezo sensor does not actually measure flow, only vibration. There could be other causes of vibration, and I think you could have flow with very little vibration.

A pressure differential across an orifice is another tried and true method of flow measurement.

A paddlewheel flow sensor is a good way to go if the original poster is concerned with the flow rate when there is flow of running the output into a totalizer which might be used to signal when to change a filter for example. Using a paddlewheel sensor would work I just didn't mention it because it didn't seem the original poster was concerned with rate of flow or totalizing flow.

Measuring the Delta Pressure across an orifice is another very good way to measure flow rate but it gets complicated and expensive. You sort of get into some extensive calculations and to determine if a small pipe has flow or no flow I just didn't see it as viable. Just my take on delta pressure based on what the original poster has shared.

Ron

 

I'd be tempted to pipe something in like you would a water softener, with a bypass valve arrangement. This would allow for maintenance and experimentation with the device without interrupting service.

No matter which method the OP chooses, this is brilliant. Well worth a little extra time and cost up front to make future maintenance and/or modification easier.

 

If you have not come up with a solution yet I saw someone mention just using an off the shelf flow switch. That is how I would go about it. You aren't concerned with the flow rate simply do you have or not have flow. All you need is a flow switch. I have no clue as to your location but here in the US switches like this are common and available from a host of industrial supply houses. I generally use McMaster Carr Supply for such needs but they can be had anywhere for a wide range in price and design. You also don't mention the pipe diameter? You mention bubbles which most flow switches really dislike.

If this is for a commercial type application I would use a flow switch as I mentioned. Since bubbles can cause problems I would use the flow switch in conjunction with a D.O.B. (Delay On Break) timer. As long as the timer gets re triggered before a preset timeout, the circuit won't dropout. This way minor perturbations in flow won't effect things. I would also power everything using low voltage DC provided by a power supply powered through mains power that is GFCI (Ground Fault Circuit Interrupt) protected. Again depending on your location.

Ron

The problem with a flow switch is that i wouldnt be able to monitor stagnant water in the pipe. If the pipe is closed but fills with water, i need to open the pipe so that flow can resume. I'm going to look into how accessible microswitches are here.

 

The problem with a flow switch is that i wouldnt be able to monitor stagnant water in the pipe. If the pipe is closed but fills with water, i need to open the pipe so that flow can resume. I'm going to look into how accessible microswitches are here.

Nope, a flow switch will not tell you if you have water lying in the pipe. A flow switch is a Yes or No switch, you either have flow or you do not have flow, the water is either moving or it isn't. However, a pipe with water in it, even if the water isn't flowing will still sag I believe. So the weight of water will be in the pipe flowing or not.

Ron