Compressor control

I have a Quincy 5120 air compressor that is not in use right now. It has pressure switch controls. I am going to need to be putting it online very soon. We have a screw compressor that is online right now providing normal compressed air. I have test cells for large diesel engines. I have an upcoming test that will be utilizing air starter to start the engine. This is why I will be needing to put the Quincy online.

The Quincy has some sort of unloaders on it I think (don't know anything about this thing yet really). Right now the compressor will turn on and off to satisfy pressure switch. In order to improve control, ease pressure settings changes, etc I want to put a PLC control in place.

I am thinking of utilizing a Click, HMI, and pressure transducers to do this. I could do all of this in my companies DAQ system, but for the cost of running conduit, and IO I could do it cheaper with a Click. Add to that the fact that I want to play.

My thoughts are.
1. To reduce short cycling of the motor/compressor I will utilize the unloaders to meet demand.

2. Turn off the motor after some amount of unloaded running time (5 mins??).

3. Watch oil pressure for safety.

4. Do you typically watch head and/or discharge temperature for safeties??



What is a "typical" control range band? 5, 10, 15psi??

This seems pretty straight forward, am I missing something??

The common unload run time I've seen is 3 minutes, then shut down motor until pressure drops.

Always monitor the head temperature to avoid damaging the unit.

If set at 120PSI (most common unless 175PSI is needed in the shop) Unload at 120 & reload at 115 or below (5PSI) - if 175PSI it's commonly 10PSI range.

g.mccormick said:

The Quincy has some sort of unloaders on it I think (don't know anything about this thing yet really). Right now the compressor will turn on and off to satisfy pressure switch. In order to improve control, ease pressure settings changes, etc I want to put a PLC control in place.

This seems pretty straight forward, am I missing something??

Click to expand...

g.mccormick,

Does your compresor have the control valve (unloader control) I have circled in the photo?


If it does then your task may be much simpler. There are adustments on this "controller" that control the cut in air pressure and the cut out air pressure.

There is also a oil pressure sensing pneumatic circuit that will "help" to protect the compressor in the event of loss of oil pressure. I say "help" because there needs to be at least 30 psi (air) for the unloader to function. So if this is the only air compressor running it will need to pump up to 30 psi to have enough air to get the unloader "hats" to unload.

If your system has the needed 30 psi (air), then the oil pressure (loss) sensing circuit will pressurize (air) the unloaders to unload the compressor until there is oil pressure.

Questions?

Add to that the fact that I want to play.

Click to expand...

Don't ever say the words "play", or "playing" while at your employer's work site. My boss once said to me, "if all you are doing is playing around and having fun, then I guess you wouldn't mind if I stopped your check this week. I see no need to pay you for playing."

Substitutes for play:
"...work with it until I learn how it works"
"...work with it to figure out how to make it perform better"
"...use trial-and-error methods to find our how it works."
"...educate myself about the complexities of this equipment"

Lancie1 said:

Substitutes for play:
"...work with it until I learn how it works"
"...work with it to figure out how to make it perform better"
"...use trial-and-error methods to find our how it works."
"...educate myself about the complexities of this equipment"

Click to expand...

LOL! The last option is the most convincing and well received.

milldrone said:

g.mccormick,

Does your compresor have the control valve (unloader control) I have circled in the photo?
View attachment 35334

If it does then your task may be much simpler. There are adustments on this "controller" that control the cut in air pressure and the cut out air pressure.

There is also a oil pressure sensing pneumatic circuit that will "help" to protect the compressor in the event of loss of oil pressure. I say "help" because there needs to be at least 30 psi (air) for the unloader to function. So if this is the only air compressor running it will need to pump up to 30 psi to have enough air to get the unloader "hats" to unload.

If your system has the needed 30 psi (air), then the oil pressure (loss) sensing circuit will pressurize (air) the unloaders to unload the compressor until there is oil pressure.

Questions?

Click to expand...

My compressor has that I believe. I haven't looked extensively at it yet, but there is a lot of tubing running around and a 3way asco valve. One reason I would want to take over load/unload in the plc is that I want to make it easier to change setpoints.
90% of the time, this compressor does not even need to run. I will set the setpoint down below the screw compressor just as a back up if we need a lot of flow for make up.
5% of the time we may need this compressor running same pressure setpoints as screw.
5% of the time we may need this compressor running significantly higher setpoints than the screw.

I would like to just type some values in the HMI panel instead of having to change multiple switches.

Lancie1 said:

Don't ever say the words "play", or "playing" while at your employer's work site. My boss once said to me, "if all you are doing is playing around and having fun, then I guess you wouldn't mind if I stopped your check this week. I see no need to pay you for playing."

Substitutes for play:
"...work with it until I learn how it works"
"...work with it to figure out how to make it perform better"
"...use trial-and-error methods to find our how it works."
"...educate myself about the complexities of this equipment"

Click to expand...

Hhaha. Yes of course.

In all seriousness, my company has a full featured data acquisition and control system (CyFlex) that is mainly used for running test cells, stands, facility control at customer sites, etc. This system is what is running our 2 test cells and the rest of the facility at this site. I could easily do the control in CyFlex, but it would be cheaper to do the local control with plc than to run communictions and install the remote IO. Plus I basically run this facility, and I can do what I want.

One reason I would want to take over load/unload in the plc is that I want to make it easier to change setpoints.

Click to expand...

You could probably insert a tee and a pressure sensor in the existing unloader control tubing, and feed that unload pressure to a PLC analog input. Then the PLC will know when the compressor is calling for Load or Unload.

You could go farther and add a small PLC-controlled solenoid valve in the unloader tube to block the load function at times when this compressor is not needed.

starting an engine takes about 25 - 30 bar, And a big starting air tank, as it takes long to fill the tank, you wont need anything fancy just a pressostat.

yes you can use the compressor to have 6 bar working pressure, but the compressor is not suited for this, so the valves will wear, as there is about 5 times more air.
it will vibrate a lot more, better is to have a pressure controller on the tank, to make working air as a backup. This air is very dry and will need attention as the rubbers will fail.

playing oke yes a small plc is good, with a pressure sensor you can measure, and with a 12 position switch and an analog (or 4 digital inputs you can set a pressure you like the tank to have.
After 30 minutes the unit will start up again as the air in the tank will be cooled down so the pressure drops.