Monitoring Pump to Avoid Dry Running

My first thought is a McDonnell/Miller type flow switch, basically a small paddle in the flow stream that operates a switch for on-off indication. These are widely used to moniter different water flow conditions and are pretty reliable and simple.

Thanks for suggsting McDonnell/Miller type flow switch. Kindly give link for more information to know about this type of switch.

Thanks

I agree. A flow switch is the best way. You can wire it to an alarm light at the 3rd floor low voltage.

I have done it for some years ago. I had a float in the tank who break the power to the pump when the level was near minimum. You can monitor if the pump is shut down and you may to start it by hand. Do you want a schematic diagram? Is the AC motor one- or three phase and what is the voltage to it? In the water you may only use low voltage i.e. 24V.

Anders

Another technique to ensure the pump is operating correctly is a pressure differential sensor connected to the pump inlet and discharge lines.

It all depends on how much you wish to spend and to what level you wish to automate you system. My personal belief is that any device that is switched on automatically should have some sort of feedback to make sure the device being switched is operating within normal parameters.

I agree. This is also a good way to monitor, other than a flow switch. A drop in calculated head.

Masu is on the right track. I always choose the controls and redundancy for any component based upon the "total cost of failure". In many instances, while the replacement cost may be trivial, the outage will disrupt other operations and cause significant downtime.

I can't recommend anything specific because I don't have the necessary detailed info of your process. But generally, at least two sensors, wired in series. A level switch and a pressure switch are the most common. Or instead of the pressure switch, a paddle type flow switch as someone else mentioned. You also need a time delay relay somewhere in the circuit to allow the pump to start back up after a trip from the pressure or flow switches. Your monitor can be a simple indicator light on the 3rd floor, activated by the relay circuit.

Or, if you've got lots of money to spend, you could go with wireless transmitters.

It seems that there is no place for the level switch to be installed (the cheapest way to avoid dry running). This method works when the suction takes place from a tank.

Flow-switch- not good enough- it has a limit under it comutes. HOW will the pump start ? On start, signal from flow switch is NO (no flow) > no command.

Yes, a pressure sensor in the suction line could work well.

Also a conductivity sensor (in the domain of potable water!) could be used as a dry sensor in the suction line (actualy for pumps are used two sensors simultaneously- a sensor for dry in the suction line and a flow sensor- flow switch in the delivery line).

Anyway, the control panel could be difficult to be done - as I know these sensors commonly generate a low signal - you need a relay between sensor wire and power wiring - the power switch/ contactor.

The pump will start under it's original controls. An additional flow switch can indicate a no flow condition.

Most rural home water systems have a cheap and simple pressure control switch to keep water pressure in the system. Some have a low-pressure cutout for when there is no water at the pump. I use such a system to fill a cistern from a dugout. There is a float switch in the cistern that is in series with the pressure switch to turn on the pump. I put a valve on the pump outlet pipe that is partially closed to keep some pressure on the outlet of the pump while it is running to keep the low pressure cutout from acting. The valve needs to be nearly closed when resetting the cutout switch and priming the pump. I am not sure why the low pressure cutout doesn't activate when the float turns the pump off. Perhaps it is the pressure from the column of water in the pipe that goes to the top of the tank.

The only problem is that it requires manual reset if the pump runs dry. Perhaps one could engineer some kind of indicator for the third floor when the low pressure cutout has been activated.

The foot valve causes the discharge line to retain pressure when the pump shuts off. Use the same system in a barn to maintain water to cattle tanks. When the pump sucks air the pressure drops and the switch turns off the system. Ric

Flow and pressure devices are difficult to physically mount and you must convert to an electric signal to get it up 3 floor. Use an ammeter on the line. Low amps means you are running dry.

"Use an ammeter on the line. Low amps means you are running dry."

I was just about to bring this up as a method for monitoring the load on the pumps but you beat me to it PetroPower.

Another thing that I was going to mention was the use of a Programmable Logic Controller. Now a PLC might sound like a lot of over kill for an installation like this but keep in mind the PLC doesn't just have to look after the pump. Once you have the computing capacity of a PLC available many other things can be wired to it and this brings a whole new lever of control and system interaction that was hitherto unavailable.

The great thing about PLC is their versatility and the ease with which they can be adapted. With a system like this all you need is the sensors, the rest can be achieved with the internal logic of the PLC. If you later find that something has been missed it a simple matter of adding the appropriate sensors and adapting the program.

Hi Masu

For 1/2 HP we must find VERY simple solutions, as you point out, that are cost affective to install downstairs, and more importantly, that Bathla can transmit 3 floors above. A CT (current transformer) put on the line (probably single phase) wired through a special CT shorting type terminal strip, and 2 wires going up 3 floor to an ammeter seems simple. Now . . . how to make it an automatic trip gets expensive (by comparison to the pump size). A current monitor with a trip point is needed. All this can be done downstairs to avoid logic wires coming and going 3 floors with only a pair of very small wires to a 'red light' up stairs. What do you think? Probably you can make it more simple for Bathla or less money, but this 'idea' is all I wanted to convey . . . that being to get away from 'mechanical high maintenance' devices to install as pressure monitors.

Thanks to PetroPower for suggestion of putting ampere meter. Since power for pump motor is fed from 3rd floor itself, Instalation of amp. meter is easy and cost effective. After observation of readings corrosponding to flow or no flow for few days will be observed and reported.

Sincere thanks

Use an ammeter on the line. Low amps means you are running dry.: Thanks for this idea, Amp meter in line gives fairly good indication of pump running dry or with load. Reading with load was 2.66 +/- 10% amps and In running dry state it was 1.6 +/- 10 %. These readings were obtained by reducing supply voltage by 20 volts to pump motor.Here supply voltage is+ 240 volts most of the times, where as pump is rated at 230 volts. In my observation with this reduced voltage to pump difference in two states of pump is more pronounced. Reasons I could not understand but this arrangements of supply to pump with reduced voltage and through amp meter has solved my problem. Now my request to forum is to suggest means to convert this two states of current readings in some sort of audible alarm circuit so that I don't have to physically monitor that amp meter.

This is going to sound like I think a PLC is the answer to just about everything but actually in a control environment they just about are. You can get a small simple PLC that cost between US$100 to US$200 that can not only monitor voltages but switch thing s on as well.

The simplest answer I can see is to get one of these and connect a CT (current transformer) to it to monitor the current going to the motor. You can also use the PLC to turn the motor on and off as well but at any rate the rest of it is software inside the PLC. You will need to write the program that the PLC uses but this is not a complicated thing and in this case all the program needs to do is check the current while the pump is running. This type of system has an added advantage that it can also be used to check if the current to the pump is too high and prevent damage that way.

Have a look on the net for PLC, there are numerous suppliers and look for one that suits your needs. If you have problems or get stuck drop me a line through the CR4 mail system and I will see what I can find that will suit your application.

Just had a thought. If the line on the suction side of the pump is city water, it will have water pressure fluctuations, and this could be the cause of the small pump running dry. To solve this, a resevoir would be needed for the pump to pump from to ensure it had the water volume needed at the suction side at all times. Almost like a day tank. City water enters the tank, float switch closes the city valve, another float switch activates the pump and pumps it to where it has to go. We are trying to treat the symptom and not the actual problem.

Want to know how to monitor from 3rd floor (1/2 hp hp AC water pump) installed at ground level for lifting water from municipal line (1M below ground) and pumping it in a tank placed at ground level.

Afterall Batla seems to want to monitor himself (including not(dry) state) and command himself the pump, . If this is true, a flow switch on the outlet with an alarm to 3rd floor is enough is enough. This was said by TLGEngrCo earlier (no command derived from flowswitch to the electric drive). Flow-switches are not very cheap (aprox 80-100 usd for non industrial applications). Can be installed in T or L in the outlet line. Anyway- a level switch for the tank has to be installed.

Yes, have to be simple (if possible).

Question (big q): the municipal line is working with a pressure high enough to fill a tank to the ground level. Isn't better to use an electric valve instead of a pump ? If the tank isn't a very high one there should be no problem (even it has, let's say 8 m hight , +1 m line-ground = 0.8 m = 0.8 bar. + 2-3 m wc presure drop = 1 bar. No problem for a municipal water line.

ALL ABOVE HAVE TO BE IGNORED IF THE LINE ISN'T A POTABLE WATER PIPE , BUT A SEWER ! Is it ?

I think there is simple solution. Just use the liquid (cheap mercury) based float valve, overload and fuse. It is very simple and economical. I worked on system using this type of control.

The standard way of doing this is by monitoring the motor power. Flow switches and floats etc. can be fooled, i.e. the pipe breaks after the flow switch or a float switch hangs. By monitoring the motor power, you know if the pump is unloaded , i.e. no flow, or overloaded, i.e. broken pipe (no head). Ammeter method is the cheap way, but can be fooled by line voltage fluctuations. The best method is a kW or torque (power factor) measuring device. Look at the Emotron M-20, or similar devices from Load Controls Inc. or Symcom Pump Saver. All of these go in the existing motor starter circuit so no external wiring is necessary.

Ammeter method is the cheap way, but can be fooled by line voltage fluctuations. The best method is a kW or torque (power factor) measuring device:

You are right, in analog amp meter it was some times difficult to know the correct status of pump ie running dry or with load.I changed to digital ampere meter.This too some times with mais voltage variation gave inconsistant readings.Voltage to pump were reducedby 20 volts by inserting a step down transformer, it increased the diffrence in current readings on load and on no load.

Regarding EMTRON M-20 device, its cost is very high for my requirment. I am looking for cost effective home solution/diy solution.

Thanks and regard for your suggestion.

you could investigate the following ideas;

1) compare amps at load and no load - could be different - should be - smart OL - deviceNet - or more easily use VFD with output according to amps or torqure (analog or digital) to your gauge up on third floor

2) Install expensive flow meter - starting at $500 up to $5000 - this will have 4-20ma output for your gauge or alarm system or PLC up on the third floor

3) intall less expensive pressure transducer in pump output pipe - i.e. the pressur eof the water should be different than air - run this analog signal up to third flloor - see IFM Efector or Omron or SMC (local guy named Scott) tell em "smarty" send you

Please explain VFD with output according to amps or torque ?