Pump Automation/Squencing

[robs68charger]

So I am working on a project but am not sure about one aspect. I am working on a system that has 2 pumps, 1 main, and 1 stand-by. Each time the pump is to turn on it will alternate which pump turns on, not a issue becasue I can just use an alternating relay. The trouble I am having is that if say Pump 1 is to turn on but does not it then needs to turn pump 2 on and alarm that pump 1 has failed. I was thinking I would install a flow switch on each pump discharge between the pump and check valve. I figured that i could use some delay relay of sorts and so when the pump turns on the flow switch has X amount of time to sense the flow and if it doesn't, then it would alarm and turn on the other pump. My question is, is this the best way to do this or is there a better way then using the flow switch and so forth? Thanks for your input and help in advance.

 

[Pumpsonly]

What type of control or sensing devices you have in mind to control the start-stop of the pumps?
IMO, a pressure switch will be better option as it does not get into the flow path.

Pump or motor failed to start alarm can also be incorporated into the motor switchboard.

 

[robs68charger]

Pumpsonly,
As far as the flow switch I was figuring of using something similar to this:

http://www.flowline.com/thermoflo_xt10.php

I thought about a pressure switch but if the pressure in the line remains relatively constant then I figured the pressure switch wouldn't work. I also guess I should explain the system a little more.

The pumps are pumping reclaimed condensate back into the system. The pumps only turn on once there is a given level in the tank.

I feel as though a pressure switch has a big contraint, it needs a drop in pressure from the intial/system pressure to be effective. This is why I figured a flow switch would be best. Maybe I am wrong, I am human and do screw up at times.

All the logic is controlled by a PLC/Smart Relay.

 

[SteveWag]

You are turning one pump on based on the level in the condensate sump. The classic way to handle the second (or “lag”) pump is to sense a somewhat higher level using a second sensor, detector or setting, depending on the level measuring device. If you are limited to one level point only, use a timer and start the second pump. If the first (or “lead”) pump starts and drops the sump, assume it’s working. If the start fails to drop the sump level in a suitable time, then the pump has failed, start the lag and alarm (and lockout?) the failed pump.

After all, the level in the sump is what matters, the pump(s) should lower the level, failure to lower, or rising level indicates a fault.

At times I have used a separate high level detector that will alarm even if the primary level sensors fail.

Steve

 

[Pumpsonly]

What is your system pressure with and without pump running?

Not sure what type of condensate (steam?) you are pumping.The flow switch you proposed did has a note that said{b]The flow sensor is best applied in applications with relatively constant temperature[/b].

Pressure sensing or flow sensing both required additional instruments and wiring between pumps and MCC.

If there is continuous of condensate inflow to sump, then level control / detection is a sure way of pump failed to start or failure
detection.

Another method is by sensing the motor current. If the motor did not start, there is no current detected. This method can be carried out within the MCC without external wiring.

Suggest you talk to your I & E department to work out the most suitable method.

 

[robs68charger]

Pumpsonly,
I had cpmletely forgot about pump failure by measuring current. This seems to be the easiest way and best way.

Thanks to everyones input.

 

[BigInch]

Pump? Or .... wire failure.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus

 

[ScottyUK]

Don't measure current. Measure power. Current measurements can give false indication, especially on high pole count motors (low speed motors). Basically the same principle though.


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If we learn from our mistakes I'm getting a great education!

 

[Pumpsonly]

BigInch,

I Thought you have been in the pump line long enough to understand that when ever a pump failed to turn or push out water, it is the pump problem.Never mind if the motor is not there or the the wires were not connected.

ScottyUK,

Current measurements can give false indication, especially on high pole count motors (low speed motors)

Would appreciate if you could elaborate your above statement.
Thanks.

 

[BigInch]

Pumpsonly, perhaps you're focusing too much on pumps. For my work I need more of a macro perspective. If my pumps don't turn, sometimes its because there's no diesel in their fuel tank, other times the operator didn't start the right one, so to make things short, I would use a flow switch.

Let your acquaintances be many, but your advisors one in a thousand’ ... Book of Ecclesiasticus