Elevated tank overflow indicator 1

[Sparky1949]

This tank is adjacent to a steep road. When it overflows, the water makes the road dangerous.

The owner wants an alarm indication when the tower overflows. Currently, there is a pressure gauge operated alarm which is not reliable due to the distance from the tank and the elevation. As the water temperature changes, the alarm either sounds when there is no overflow or fails to sound when water is overflowing. (Yes, it has been calibrated.)

Due to icing in the tank, I am thinking of putting a paddle switch outdoors on the end of the overflow pipe after the varmint screen. The only problem that I see is that the paddle will be exposed to vandalism. Is there a common practice for this situation?​

 

[fegenbush]

Do you have an external level indicator on the tank? If so, it may be possible to use that target board and install a limit switch to activate the alarm when the float reaches a certain height. It would be high enough on the tank for vandalism to be of no concern.

 

[JStephen]

The proper approach is to set up the system so the tank doesn't overflow. That's an emergency device to prevent failure of the tank, and shouldn't ever be used in normal operations.

You might check with an electrician or alarm company. I've seen roof manways wired to trigger an alarm when opened, but not sure of the details- but assume you could wire a flap valve in a similar way. This is not a common procedure, though.

 

[LittleInch]

Sparky,

Your post needs a bit more info to make sense of it.

"When it overflows" sounds like this is a common occurrence and hence there is a lack of flow control into the tank. Is there any? Is the overflow actually the normal operation? If so it should go somewhere safe.

"Currently, there is a pressure gauge operated alarm which is not reliable due to the distance from the tank and the elevation." - Sorry, this doesn't make sense. Most tank height gauges derived from hydrostatic pressure I know of are bolted to the tank and work very well. if your connection point freezes, then that is a different issue and it either needs insulation / trace heating or maybe a much bigger pipe or get a submersible one.

It is not clear whether you have power available at the tank, whether you can run a cable - what's wrong with a simple float switch powered from your remote location?? - what your design limitation are. Therefore it is difficult to help you as much as everyone would like to.

A sketch / diagram / photo and a bit more explanation as to why this tank overflows and what you particular circumstances are would help a lot.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Sparky1949]

Thank you for the responses. I'm back from two weeks on a secure site. Sorry for the offense of not responding. I've been very distracted by work.

The tank is an AWWA water tower with no external level indicator. While there is power at the tank, the underground communication wires have been broken several times. Others have modified the alarm by installing the pressure gauge, first next to the pumps,then at the wall of the pump building 800 feet away from the bottom of the tank and about 200 feet below the bowl. Rather than trenching 800 feet and across a road, I'm planning to install a Radio link.

The tank is an onion shape, so I'm putting the level sensor on the bottom of the bowl. Even so, I don't want to depend on the level sensor for an overflow indication. (Yes, the tank is overflowing on a regular basis. This is the reason for this post.)

Float switches only work until the water freezes, then they break. Condensation constantly forms in the overflow pipe, so resistance water sensors don't work reliably ether.

I'm thinking of a paddle switch which aren't susceptible to false alarms,but they could be damaged by ice coming down the overflow pipe.

Sorry for the lack of a sketch. I'm not working at a desktop computer, just a cellphone. The browser has crashed four times just writing this response.

Thanks again.

 

[LittleInch]

sparky,

My point and that of others is that there should be some sort of control to prevent the tank overflowing. I would have thought that the owner would want the tank to not overflow in the first place, not find out about it after the event. From your description I'm not surprised the pressure gauge idea didn't work if it had interference from the pump line - Is there a way of disabling it when the pump is running?

maybe you need something like this to rig up to your radio link?

http://www.sulzer.com/en/Products-a...s/Submersible-Pressure-Sensor-Type-ABS-MD-127

You should be able to use this for control to prevent overflows?



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[bimr]

Install an (insulated) pressure transmitter at the base of the tank tied into the SCADA. The SCADA should have setpoints that will alarm. This will be the least expensive option.

If you do not trust the pressure transmitter, install a backup. That would be a separate pressure switch which will tie in to the control system to shut down the pumps.

Storage tanks should not normally overflow. High alarm level on a tank is typically set at 90% full. The overflow is a contingency in case of failure to shut off the incoming water.

Installing a paddle switch for an event that should not be happening is kind of pointless.

 

[Sparky1949]

LittleInch and bimr: Control is indeed a given. That is the reason for the project in the first place. I have a transducer, Radio system, Level control, and pump control already.

Since I was asking if there was a common practice for an overfill alarm, I think the answer may well be NO. I know I have never seen one on the dozens of tanks I have climbed. Generally, the level is controlled by an altitude valve at the base of the tank.

Yes, you are quite right, it may not be necessary to have an overfill alarm once the transducer is installed in the correct location and the pumps are controlled correctly. However, the owner wants a definitive (not based on pressure) overfill alarm.

Perhaps I will install a resistance switch on a weir at the overflow inside of the tank...

 

[bimr]

Here is a recent project. Note there is a sensor in case of a leak at the base.

 

[Sparky1949]

Thanks BIMR!

That is a good idea. Thanks also for the drawing.

Unfortunately, the outfall for the overflow is outdoors and the float switch will be triggered by rain.

It seems to me that the best way is to install the flow switch in the overflow pipe. Now that I think about it, the switch could be anywhere in the pipe and that would include inside the riser of the tank.

Thanks everyone for your comments and time.

I'm going to stop watching this thread now.