Drawing Pump Schematic

[balash]

Seems like there are a few ways to do this control. 2nd rung is obsolete ? Is that because on a ladder control drawing, you don't need to show the pump motor itself ?

it's because control and power circuit are two different thing, sometimes even with different voltages (24 VDC / 230 VAC).

i assumed that connecting 1-phase or 3-phase motor to electric grid (ie power line, with all contactor, o/l relay and fuses) are not the problem here.

but for completness of all that would be, for 1-phase motor:

L1 -> Fuse -> contator power contact -> o/l power contact -> motor

 

[Lancie1]

Simulating Balash's relay logic on the LogixPro Simulator, the Low Level in Parallel with the Start PB seems to be the desired method. It allows manual testing using the Start PB, Stop still works, and the level switches operate to maintain the tank level between 100 and 450. (The low level switch should be NC at less than 100, and the high level should be NC at less than 450).

Locating the switches in the relay circuit as shown will result in the fewest feet of wire to be run between the various devices, assuming that the float switches are closer to the motor starter than are the Start & Stop PBs.

If the the Start and Stop are physically close together and are closer to the motor starter (in a control room or on the motor starter) than to the high level float switch, then the positions of the High Level Float Contact and the Stop PB should be reversed.

 

[Tom Jenkins]

The schematic depends on your desired operating sequence. Most of the above examples require manual initiation of the pump run. That may be OK, but usually you want the high level float switch to start the pump without manual intervention. You then usually want the pump to run until the low level float switch drops out, indicating the wet well is empty.

Until you describe the sequence, nobody can say what is right for you or even what will work.

Attached is an example for a duplex pump system with float switch control. If you want manual OR float switch operation then put the start button in parallel with the float switch.

 

[bernie_carlton]

Tom, I think the OP's description was for a 'pump up' control rather than a 'pump down' (like a sump pump) operation.

 

[Lancie1]

He wants to have a tank with 100 gals minimum, and have it stop pumping liquid in after the tank reaches 450 gals.

Yes, we need to pump the tank fuller. The original drawing is a clue that the Stop and Start Pushbuttons are desired, even though the float switches may override those at times. If the STOP must always stop the Pump, then probably another relay will be needed, or the STOP function will need a maintained-contact switch.

 

[Tom Jenkins]

Your right, Bernie and Lancie. I wasn't trying to do his work, just point out some techniques. Sorry if I caused confusion.

 

[balash]

i work with these schemes all the time. this particular one i use for pumping drinking water to reservoir, and Tom's way i do in sewage system.
as from practice, i can say that float switches, though simple for maintenance require lot of cleaning when used in sewage system, so i started to change them for wastewater hydrostatic probes. (good for now, should try ultrasonic yet).

 

[dronai]

Thanks for all the replies. In Tom's example he shows 3 floats yes ? Is that lead lag, and alarm ?

In balash's changes, he shows the LL Float NO, or is that in use ?

 

[Lancie1]

Tom, that is an interesting schematic that you posted. I don't think I have seem many motor starters that do not have the OverLoad relay contact connected to the right of the contactor coil, nor have I seen many that do not have the auxiliary seal-in contact connected to the left side of the coil. Did this come from a college textbook?

 

[Lancie1]

In Tom's example he shows 3 floats yes ? Is that lead lag, and alarm ?

I think Tom's example is Pump 1 from a 2-pump Lead-Lag system. There should be a dotted line connecting the 2-pole Lead-Lag switch between the Pump 1 schematic and the Pump 2 schematic. When the Lead-Lag switch is ON for Pump 1, it should be OFF for Pump 2, and vice-versa. The HH (High-High) is normally used for an alarm, but in this circuit it is only being used as a backup for the High Level Switch. If the pump is in the Lag mode, the High Switch will not operate the motor, but eventually the HH switch will act as a backup if the level keeps rising with the other Lead pump working, and would start the pump (so both pumps run at the same time).

In balash's changes, he shows the LL Float NO, or is that in use ?

For float switches, you really cannot define NO or NC very well unless you say at what relative liquid level you are talking about. The traditional definition that normal is how it is laying on the shelf before being wired into the circuit does not work very well. For your pump to maintain a level, you want your Low Level switch to close on falling level (100 or below), and your High Level switch to open on rising level (450 or above).

Then for each time a float operates a float switch, you can have multiple switch contacts, some of which are open while others are closed.

 

[balash]

In balash's changes, he shows the LL Float NO, or is that in use ?

to clarify myself i shall say this:
LL float switch must be closed below the (minimum) level
HL float switch must be closed above the (maximum) level

some general clarification:
float switch are designed as c/o contact so that user can wire them as needed.
the would mean that you should hang the float switch and see what contact is ON - now that contact you need for LL
now raise switch until click is heard - the other contact now is o+ON and that would be HL

as for overload relay and fuses, you can bypass all that with motor protection switch like schneider GV2 or GV3 that have built-in thermomagnetic protection.
that way you just need to wire its aux contacts for trip (and/or state of switch)

 

[Lancie1]

HL float switch must be closed above the (maximum) level

The action of float switches is so confusing that even the experts get confused.

If you are filling a tank or maintaining a level in a tank, you want the High Level switch contact to be closed until the maximum level, then open at the maximum (open on rising level) to stop the pump.

as for overload relay and fuses, you can bypass all that with motor protection switch like schneider GV2 or GV3 that have built-in thermomagnetic protection.

Yes, true, but Tom's schematic drawing was for a traditional U.S. NEMA-type Size 2 combination motor starter (where the OL is a relay contact wired to the right of the contactor coil).

 

[Tom Jenkins]

Tom, that is an interesting schematic that you posted. I don't think I have seem many motor starters that do not have the OverLoad relay contact connected to the right of the contactor coil, nor have I seen many that do not have the auxiliary seal-in contact connected to the left side of the coil. Did this come from a college textbook?

Close. This is a simplified example I drew up to demonstrate reading schematics as part of a course for process operators. It is only intended to show the logic operation of the holding contact "M" and series and parallel contacts, which is why I used it here. (I'm actually a little sorry now that I did! It seems to have created more confusion than clarity.)

Most O/L contacts do switch on the neutral side. Some don't, or at least can be wired the other way and I prefer that.

Many float switches have SPDT contacts.

The intent is to show how the LSH can run one pump - the lead - and have LSHH run both pumps. LSL will stop both pumps.

There are a lot of other devices not shown in my schematic. E-Stops, leak detection switches, etc.

 

[Lancie1]

(I'm actually a little sorry now that I did! It seems to have created more confusion than clarity.)

I guess we have beat it to death, and it is past the time to quit.

 

[danw]

action of float switches

Gems defines the float switch condition as 'dry':