All the elements of the KISS principle in one paragraph...

That's my job here. We have plenty of people that can type all day and include minutia that 95% of the beginners will never be able to measure or use for their purpose. I'm the counter balance for them.

 

Eek! I'm afraid I'm both sometimes: I type all day about minutia, while also being a beginner who understands little. Concise has never been my strength, but I'm working on it!

 

Eek! I'm afraid I'm both sometimes: I type all day about minutia, while also being a beginner who understands little. Concise has never been my strength, but I'm working on it!

One never actually stops working on anything... no matter how much of an expert one becomes... the important thing is to never stop trying to improve

 

Absolutely! The day you stop learning is the day you become useless.

 

Could you please clarify? Do you want to detect the presence of water in the pipe, or do you want to sense flow, however small? Does the pipe completely empty when this condition you're talking about takes place? I might have a few ideas that could help you.

Yes, i want to detect the presence of water in the pipe. Flow isnt important. The pipe doesn't completely empty but it will be almost completely empty. I'd like to avoid putting holes and such in the pipe.

 

The PVC pipe will sag a maximum at the mid point between the supports and will sag more when the pipe is
full than empty The pipe must be adequately sloped so that it does not store static water.
The amount of sag is proportional to span, diameter of pipe and geometry of pipe, none of which changes.
The sag which can be easily monitored with an external micro switch is dependent only on whether there is
water in the pipe or not.
See post 13.

 

Yes, i want to detect the presence of water in the pipe. Flow isnt important. The pipe doesn't completely empty but it will be almost completely empty. I'd like to avoid putting holes and such in the pipe.

A few last questions:

1. What's the maximum pressure in the pipe?
2. You mentioned that the pipe is 3/4" internal diameter and that it has a wall thickness of 5mm, is that correct?
3. What's the total length of the pipe that can be worked with for this purpose?
4. What's the approximate slope of the pipe within the pipe's workable length?
   
5. If you'd like to avoid making holes in the pipe, would you be willing to cut it and insert another segment with a device installed in it for this purpose?

 

When our tanks arent filling we need to close our main pipe and open up a different pipe ...

Isn't it possible that the filling will also stop if the tank becomes completely full?

Seems to me that a level indicator on the reservoir tank would be a better solution. By monitoring the level you could detect when the takeaway is drawing it down too fast. You could apply an adjustable algorithm that decides when to switch into restriction mode, using some combination of ∆level/∆t and current tank level, or whatever you like. You may also find it very useful to have the tank level reading available continuously.

 

A few last questions:

1. What's the maximum pressure in the pipe?
2. You mentioned that the pipe is 3/4" internal diameter and that it has a wall thickness of 5mm, is that correct?
3. What's the total length of the pipe that can be worked with for this purpose?
4. What's the approximate slope of the pipe within the pipe's workable length?
   
5. If you'd like to avoid making holes in the pipe, would you be willing to cut it and insert another segment with a device installed in it for this purpose?

1. Not sure about the maximum pressure. I'm sure we could measure the pressure when there are no obstructions to get a rough idea, but we'd have to travel to la paz to buy some sort of pressure gauge.
2. correct
3. We have meters of pipe that can be worked with.
4. I'll get back to you on slope.
5. Yes, we could do that.

 

The PVC pipe will sag a maximum at the mid point between the supports and will sag more when the pipe is
full than empty The pipe must be adequately sloped so that it does not store static water.
The amount of sag is proportional to span, diameter of pipe and geometry of pipe, none of which changes.
The sag which can be easily monitored with an external micro switch is dependent only on whether there is
water in the pipe or not.
See post 13.

thanks, i'll look into microswitches.

 

Isn't it possible that the filling will also stop if the tank becomes completely full?

Seems to me that a level indicator on the reservoir tank would be a better solution. By monitoring the level you could detect when the takeaway is drawing it down too fast. You could apply an adjustable algorithm that decides when to switch into restriction mode, using some combination of ∆level/∆t and current tank level, or whatever you like. You may also find it very useful to have the tank level reading available continuously.

Our tank is large enough that we never have a condition where our tank is completely full. If our pipes never got clogged i'm sure we would with time but our pipes get clogged 3 or so times a week.

 

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

 

Other than the flow switch already suggested. What I was going to propose is to cut a segment of the pipe, and then add a long "U" shaped segment to it. If what you want is to detect the presence of water in the pipe, this could be a very practical way of doing it, by just measuring that segment's weight. You could place a microswitch below that segment of the pipe with a calibrated spring that would react only when a measured amount of water is trapped in it. The water's weight inside the pipe's "U" segment should be able to exert enough torsional force on the pipe's main segment for the switch to be actuated or not.
The downside of this approach is perhaps that maybe the switch would be sensitive to vibration in the pipe due to discontinuities in flow. To remedy this, you could add a timer circuit that would only actuate a "water - no water" signal after the pipe has remained stable for a certain amount of time.

 

I also like the micro-switch suggestion. I have a lever actuated micro-switch sitting here and at the end of the lever it really doesn't take much weight to trigger the switch. If the switch were mounted with a pre-load I am guessing roughly .3 Oz of force. As long as with no flow there is water not sitting in the pipe enough to weigh it down.

Ron

 

I like that idea, but I'd use a loop of PEX tubing instead of PVC. Less fittings, very easy, flexible by design.

 

I like that idea, but I'd use a loop of PEX tubing instead of PVC. Less fittings, very easy, flexible by design.

Sounds good too... my suggestion of using the same pipe material was for consistency reasons, that would mean that tooling and the storing of spare parts wouldn't change.

 

Yup, it's up to the OP to choose whatever is convenient for him. I've just been working with PEX for the first time and I'm learning how useful it is. Actually, it is not meant for UV exposure, so may not be a good choice for this project if it is exposed to sunlight.

 

@ cmartinez , Reloadron , wayneh.
Did you see post 13 and post 26 ?

 

@ cmartinez , Reloadron , wayneh.
Did you see post 13 and post 26 ?

Yes I did, but I understood your idea as measuring how much the pipe would sag. Which would rely on its linear distortion along a straight segment. My proposal, while being similar to yours, is based on the pipe's torsion due to its weight, and I personally feel it would be more resistant to vibrations and changes in ambient temperature, and more reliable at the same time.

 

Me too. I'm not wild about pipe sag or bend methods. (My favorite is still what I suggested in #3, to cheaply measure flow. Collecting flow data over time might be useful to the OP in ways that are hard to predict.)

Where I live, the temperature can easily swing 125°F in one year, and pipe stiffness would vary tremendously (not to mention freezing water). But I concede the method will probably work for this project. 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.