Control Circuit for Air Compressor

Oh my God, Such a Big question.

<...How does the control circuit work to auto start the motor again when pressure is low....>

Item P, the pressure switch, controls the motor on pressure.

<...What is the function TM3, load solenoid valve, blowdown solenoid valve and how it controls the motor....>

TM3 doesn't control the motor. It only operates the blowdown valve, which is there to blow any water and/or dirt out of the bottom of the unit's air receiver vessel.

there s something wrong wit your circuit. for eg, the overload contacts mol-1 & mos-1 are in series and tht too in NC and NO position, making it impossible for a closed circuit at any instance, check it properly and please provide a proper diagram. if i zoom on the picture , it fades, so upload a better quality picture.

Load solenoid controls when to 'load' the compressor...make pressure. Unload is what is says 'unloads' or blows down the compressor i.e. makes 0 pressure. Unload is when the compressor meets the upper psi setting and stops making air. Or during shut downs it will blow down, unload the compressor. Without an unloader you would have a run away compressor until the popoff valve(s), Kunkle valve goes or a pipe bursts.

How does the control circuit work to auto start the motor again when pressure is low.

Mainly your complete circuit is working on the pressure switch only. If you go through the circuit. As soon as KM1 contactor picks up, the KM1-2 NO becomes NC and the valve gets the supply to operate. As soon as the switch gets to 120Psi it change over to TM2 creating a 6 min. delay, by cutting of the compressor supply through TM2-1. so the compressor is off for 6 min.

When the pressure becomes low again the pressure switch switches back to solenoid circuit, where TM2-1 becomes NC again and pickups KM1 contactor and compressor gets supply. the cycle starts again.

What is the function TM3, load solenoid valve, blowdown solenoid valve and how it controls the motor

TM3 is timer for high air temperature, where if HATR relay trips due to High air temperture, then as you reset the HATR relay the timer starts the delay before the KM1 contactor is cutoff through TM3-1 NC.

After having a look at this circuit, I wonder who has designed it?

PMR - Is the Phase rotation relay, this is to ensure that the compressor is operating in the correct direction.

TM1 - Should have been the start up oil pressure time delay, but there is no compressor oil pressure switch, and this should never be used across the PMR.

TM2 - In high use air situations the compressor motor may not be rated for to many starts per hour, TM2 keeps the compressor motor running for up to 6 minutes to allow for both the air cooling of the compressor and the posibility that the air pressure may drop within that time frame and resume compressing air without need for restarting the compressor motor.

TM3 - Is used for unloading loading the compressor when starting to reduce the starting load (ie compressor pumps no air for TM3 time 10 seconds).

To be honest this apears to be a very poor design, has it worked at all?

Where was this compressor supplied from?

I presume on TM1 terminals 2-7 are the timer coil circuit? And 8-5 are the relay contacts, are these NO or NC? This is not my idea of a good design.

I hope this is of help, any further questions please reply.

Cheers

Joe

Hi.. thanks a lot for the reply..

I have checked the contacts for the timer.. for TM3-1 is a NC contact with time delay while TM3-2 is a NC contact which opens when the timer is coil is charged.

And for TM1, yes, terminal 5-8 is NC with time delay.

MMS-1 is a manual switch that needs to be closed to allow starting.

Isn't TM3 used to delay the shutting off of the motor when we turn the selector switch to 'off' position?

This is actually an Ingersoll rand M37PE air compressor but the circuit has been modified by the local supplier.

Well if you put it that way, what point has TM1 got to do? You must understand that PMR should be closed anyway if the phase rotation is correct and why would you want the compressor to operate at all if it is going to go the wrong way?

Usally on a good quality air compressor you would have a timer that by-passed the oil pressure switch on startup, the oil pressure switch being a NO contact and closing on reaching a minumin oil pressure. IE: Start the compressor for 10 seconds then if no oil pressure, stop compressor right away. To attempt a restart you would have to manually press a reset switch usally.

The other strange thing about this part of the circuit is that TM1 coil is not wired through the control circuit, it is wired through the power circuit the only circuit protection on TM1 ciol and the PMR phase supply is the main supply which according to the Ingersol-Rand data could be from 40 to 80 amps. This is a very very bad idea, it should be wired through the control circuit.

MMS1 should be closed at all times, not just to allow starting, it must be closed to allow the running of the compressor.

TM3 looks like a shut down timer, but the circuit to me makes no sence.

Honestly if I were you I would go back to the local supplier that modified the circuit and start asking some serious questions.

1. Why are TM1 and PMR not protected by some sort of overcurrent protection?

2. What is the purpose of TM1?

3. Can the local supplier supply a flow chart, or sequence chart of operation?

I agree with you on the TM1 part. It makes no sense to bypass the PMR.

About the oil pressure switch, even the original circuit is without the switch. If I were to install an oil pressure switch, I need to install it in series with HATR-1 switch and connect the TM1 timer across the oil pressure switch? Am i correct? So if oil pressure drops, the switch will open and deactivate KM1.

For the PMR over current protection part, can i install fuses on L1, L2 and L3 to sure it is cut off when over current occurs?

Thanks for your help.

About the oil switch, I dont think that your idea would work, because the Oil pressure switch is NO at low pressure, how will you ever reset the HATR-1 it just wont work.

Has this compressor control worked at all?

Installing fuses on the PMR would be a good idea say about 2 amp, but this wont protect TM1.

Honestly the circuit needs to be re-designed

Cant you go back to the suppliers, and ask them to fix it? Or is there something that you are not telling me?

You have evaded the question that I have posted earlier on in this discussion, has the compressor run at all?

If you fill me in on the full story, I will be in a beter position to help you!

Best Regards

Joe

Hi,

If i'm not mistaken, there are oil pressure switches that have NO and NC contacts in the market such as this.. http://www.fwmurphy.com/psb/

It seems like after HATR is activated, there are only 3 ways to deactivate it. Open MOL-1, MMS-1 or HATS contacts. Now, if i put a NC oil pressure switch which opens at low pressure in series with MOL-1 and MMS-1 or HATS, I could deactivate HATR when the oil pressure switch opens. TM1 will be removed from PMR and installed across the oil pressure switch to bypass it during start up. Can this work?

The compressor is working, but it is not tested in the field yet. Which part of the circuit do you suggest need to be designed? About getting back to the supplier, i'm not sure it's possible cause the compressor was supplied few years ago and our company have accepted the compressor without prior checking. I'm now assigned to check the compressor and will need to highlight any issues and make suggestions to improve the compressor. My superior will then decide whether or not to seek the supplier to rectify the problems.

Hi

Sorry mate things have got a bit busy. I will reply as soon as I get back home.

Cheers Joe

First of all, this circuit is not properly traceable. And even this circuit is not completely correct. There is something wrong in this circuit.