# Understand unloader valves



## Karl_T (May 2, 2019)

I bought a nice ten horse quincy air compressor  at auction. Worked there, not when I got home  

First was electrical. installed new contactor and relaced burnt up wiring. Still no joy.

Went completely through head. Removed ten pounds of burnt carbon several reed valves and springs. Man was it a dirty mess. Still does not run, but I am close.

The unloader valve is not releasing. If I undo the unloader valve air line at the blue arrow in the top of quincy pic, the compressor begins pumping.



Look at the unloader valve assembly - side of quincy pic.

I think this stuff is for both an engine type compressor and an electric motor start unit.








Now look at my tractor PTO unit.  This compressor only unloads on high pressure allwoing the PTO to keep turning. Sure looks exactly like the parts in green arrows on the quincy.


Back to the side of the quincy. I want to verify this, but I am pretty sure I've seen compressors with only the bottom device (red arrow in side of Quincy view). So, am I right? all the stuff in the green arrows has nothing to do with starting unloader operation? So, it can be removed?  FWIW, the valve ,orange arrow, is turned off.

That still won't get it working. My guess is replace the bottom, red arrow, unit. plumb it direct to the unloader valves on top the compressor.

I may be all wet here, sure would like to find someone that know how it is supposed to work.


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## matthewsx (May 2, 2019)

I can’t help with your specific problem but definitely find an expert who understands your unit. Also make sure the tank is good before running it up to pressure, they can be deadly. I have a local compressor service company that always gives good advice, if I hadn’t gone into their shop my compressor would still be wired wrong. I also changed to a lower pressure switch that stresses both the motor and me out less.

Cheers,

John


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## Latinrascalrg1 (May 2, 2019)

So to understand what your dealing with, you have an electrical air compressor that is not working if there is pressure in the line between then head and the check valve?  If yes have you checked the start and run capacitors (assuming that it has them)?


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## Karl_T (May 2, 2019)

electrical end is fine, motor starts and stop with pressure switch.

There is always air pressure to the unloaders  on top of the air compressor so the reed valves are held open and it does not pump.

Correct operation is for the unloaders  to be held open for a few seconds while motor gets up to speed. Then they close and it starts pumping air. Unloaders are present on large compressors to reduce startup load.


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## Latinrascalrg1 (May 2, 2019)

Ok so regardless if the motor side is working or not the Unloader portion should be holding the "Start Valves" Open so that there is no pressure at startup, Yes/No?   So the next questions would be,  What tells the valve when its time to close and how is it activated?


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## Karl_T (May 2, 2019)

I am a bit in the dark on how it works, that's why the query.

I can tell it is backward from your description. It takes air pressure to the unloaders on top to depress them and disable the reed valves. That's why it pumps when this air line is disconnected.

I *think* air pressure in the crank case is the switch, not real sure. but there is a connection to the crank case. I *think* that's what the bottom device , red arrow, does.


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## Karl_T (May 2, 2019)

here's the parts manual for the unloader control parts.

Mine has dual controls with pilot valve.

It shows an option for hydraulic unloader only. I *think* that's what i should go to and then repair / replace the hydraulic unloader.


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## JimDawson (May 2, 2019)

Karl, I think you're on the right track.  It looks like the starting unloader is activated by oil pressure.  You might put a gauge on the oil pump and see if the oil pump is working.  Or maybe the shuttle is just stuck.


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## Latinrascalrg1 (May 2, 2019)

Ok looking over a few different  styles of the unloader valves there seems to be 2 default settings either  Normally open or Normally closed.  Either way it sounds like your valve is stuck but not sure whether that is stuck open or closed!  This is probably being caused by a broken/corroded spring and or Ball bearing inside the valve which may be replaceable.


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## westerner (May 2, 2019)

One old compressor I am familiar with uses a centrifugal unloader. Flyweights on the crank move to open (or close, I can't remember) a valve that controls the reed valves. With this gizmo stuck, the reed would be held open, and no pumping going on. This type of mechanism is located on the end of the crankcase, centered about the crankshaft. Air line running from the unloader housing to the cylinder head relays the signal. No oil pump at all on this compressor.


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## Superburban (May 3, 2019)

There is two types of unloader valves. The ones most are familiar with, unloads the pressure from the head, to the tank when the motor shuts off, making it easy to start up the next time. The other style, many big compressors have, unloads the head, when the pressure is reached, (Like what is used on gas driven compressors,) So the compressor stops pumping, but the motor can still run. Some setups will turn off the motor, and some leave it running (Do not know why, but I had one).  Those look like the second style. 

Yes, you can remove ort bypass the parts you are looking at. The unloading you want is the one that releases the air in the line from the compressor to the tank (assuming the is a one way valve at the tank).


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## Cadillac (May 3, 2019)

Above post is right on about the unloader valve. Looks like you have a lot going on there. Here’s a pic of my Quincy at work same configuration kind of. I don’t know why they have that gate valve in your setup. The unloader is a one way valve that releases air pressure off the line so the compressor isn’t pressurized when motor starts up. 



Valve on top of head is piped to square valve on side of block. From that box it goes to the tank gauge not in view. Other small line going in side of head is a oil line coming from crankcase. Are your relief valves working. Their the valve with the key loop thing hanging off the end. They open when you max pressure is reached.


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## Karl_T (May 3, 2019)

Ok, if you search long enough, you can find anything on the web. I attached an exploded view of the hydraulic unloader assembly on my unit.

My plan will be to remove every unloader control not needed and go to the hydraulic unloader only option from the .pdf I found in post 7. install new piping and rebuild the hydraulic unloader.

Stay tuned to see if it runs.  Right now, this is spare time when i'm bored. My other compressor is making a bad sound. If/when it dies, this will be top of the list.


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## FOMOGO (May 3, 2019)

I have that same pump in the older splash oiling style. Started rebuilding it last year before I left for the winter and should finish it up soon.The one thing I can tell you is that Quincy doesn't use a check valve between the pump outlet and the tank. As said above the unloader dumps pressure at the the head when set pressure is reached, a very distinctive sound. I got my rebuild kit from these very helpful folks (see below) Mike



Pacific Air Compressors

                                                                                                       3009 NE 172nd Place                                                                                                                                                            

                                                                                                       Portland,  OR   97230                                                                                                                                                                                                              503-674-2744                                                                                                                   
​


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## Karl_T (May 3, 2019)

Mine looks to be splash oiling also. Not sure but see no pump system in the parts manual.  I will pull the hydraulic unloader and turn over the unit to see if it spurts oil to know for sure.

??  Do you sell parts?

I am looking for a hydrauliuc unloader repair kit. Part number 8063 from this very old manual. see my post 13.


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## Cadillac (May 3, 2019)

Google should be your friend just typed in that part number and this is what came up.


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## Karl_T (May 3, 2019)

What did we ever do without the inter web net?


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## Karl_T (May 8, 2019)

OK, got the hydraulic unloader rebuild kit  and spent the morning cleaning and rebuilding the unit.  kind of tricky but pretty sure it was assembled correctly.

But it still did not work.   it is always letting air pressure through. So, I'm beat on this route.

 I just ordered an air solenoid and a delay off timer from McMaster Carr. I will control the unloading at start up electrically. stay tuned to see if this works.


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## Karl_T (May 15, 2019)

Update. Got the unloader working with an air solenoid and timer. This may actually be a better way to do things as you now have total control of when to bring in the  compressor.

OK, all this is only with the RPC running. I want the compressor to run on single phase power, so I ordered this VFD:





						CNC 7.5kw 7500w 220v 10HP 34a 10hp Variable Frequency Drive Inverter VFD for Spindle Motor Speed Control - - Amazon.com
					

CNC 7.5kw 7500w 220v 10HP 34a 10hp Variable Frequency Drive Inverter VFD for Spindle Motor Speed Control - - Amazon.com



					www.amazon.com
				




One question, do these VFDs have the ability to fire an output when they are up to speed?  it would work GREAT to engage the unloaders only after the VFD has made full speed.


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## JimDawson (May 15, 2019)

Karl_T said:


> One question, do these VFDs have the ability to fire an output when they are up to speed? it would work GREAT to engage the unloaders only after the VFD has made full speed.



Most VFDs have a programmable output that can be programmed for ''At Speed'', not sure about this specific model.


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## Karl_T (May 15, 2019)

Thanks, I thought so. bet this is a copy of top end VFDs and has the same functionality. the Chinese are good at copy  

Just need to brush up on my chinglish, bet the manual on this thing is poor. I got till June 5 - long delivery time.


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## mksj (May 15, 2019)

Assuming you are using an HY VFD, you might look at PD050-51 (Multi-output 1 (DRV/UPF)), if programmed to 05 = Set Frequency Reach on the HY model. This would trigger DRV output rated at 24V/100 mA so this could trigger a relay to control a solenoid. Also there is PD052-53 which operates the relay for FA, FB and FC; KA and KB. They do not give a description, but it should operate with the same parameters as PD050 "Multi-Output", so setting it to 05 = Set Frequency Reach should also work. The relay is rated at 3A/250VAC/30VDC so should be able to directly operate a solenoid. Other option is a delay triggered solenoid set at something like 3-5 seconds.

If your compressor has an oil pressure gauge, then it uses a pressurized lube system.


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## newbydave (May 15, 2019)

mksj said:


> Assuming you are using an HY VFD, you might look at PD050-51 (Multi-output 1 (DRV/UPF)), if programmed to 05 = Set Frequency Reach on the HY model. This would trigger DRV output rated at 24V/100 mA so this could trigger a relay to control a solenoid. Also there is PD052-53 which operates the relay for FA, FB and FC; KA and KB. They do not give a description, but it should operate with the same parameters as PD050 "Multi-Output", so setting it to 05 = Set Frequency Reach should also work. The relay is rated at 3A/250VAC/30VDC so should be able to directly operate a solenoid. Other option is a delay triggered solenoid set at something like 3-5 seconds.
> 
> If your compressor has an oil pressure gauge, then it uses a pressurized lube system.





Karl_T said:


> I bought a nice ten horse quincy air compressor  at auction. Worked there, not when I got home
> 
> First was electrical. installed new contactor and relaced burnt up wiring. Still no joy.
> 
> ...


Make sure your motoris turning in the right direction. The oil pump will only work if it is turning in the right direction. What is the pressure on the guage when it is running.


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## Karl_T (May 15, 2019)

Thanks for the detail on the outputs, thought HY VFDs had this. This is going to be the PERFECT way to control the unloader valves.

Yep, this unit has an oil pump. I checked it with the hydraulic unloader removed => oil slick across the room.


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## Karl_T (Jun 2, 2019)

OK, been a while. I ordered a Huanyang VFD on a slow boat from china. My ship finally came in this week.

Pic shows everything mounted and wired except the unloader solenoid valve.

This is the programming:
1. Remote
    a) wiring:  S1 and comm through pressure switch and on/off switch in series
    b) parameters
        P0.01 to 1   Remote terminal
        P5.01 left at default 1  forward run

2. Speed control parameters
    P0.03    max freq        60
    P0.04    U F L              60
    P0.05    L F L               60
    P0.06   ref. freq.          60

3. accel and decel parameters
   P0.11   AC time     5
   P0.12   DC time     5
   P1.06   stop mode 1  (coast to stop)

Machine run fine!!!!!!   Big day for me. been working on this a LONG time with a mechanical rebuild, then a failed unloader rebuild, then an electrical unloader test, then the VFD install.



OK, ONE JOB LEFT.  Would like advice before proceeding.

Need to energize the 110 VAC air solenoid to the unloaders ONLY during machine acceleration.
I copied the four pages about this from the manual. See .pdf

Got a relay output: R01B (NO) and R01C. (NC)  can put 110 VAC to R01A common
Can program this P6.02 to 6 frequency reached. manual references P8.23, leave at defalt of 0.0

Have an extra contact on the pressure switch.

I am thinking run 110 power to pressure switch then to R01A. Then connect R01C to hot side of air solenoid.

If pressure switch closes => 110 goes to air solenoid. When frequency is reached  R01C opens.


<EDIT>  Maybe there are TWO outputs. manual is confusing here. Looks like terminal strip has a second set of outs and manual reference P6.03 for output 2.   If so, I'd use this instead of pressure switch.


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## JimDawson (Jun 2, 2019)

Karl_T said:


> I am thinking run 110 power to pressure switch then to R01A. Then connect R01C to hot side of air solenoid.
> 
> If pressure switch closes => 110 goes to air solenoid. When frequency is reached R01C opens.



If I understand correctly that should keep it unloaded until the motor is up to speed.  I have found on mine that just having a 10 second accel ramp works fine, but I only have a 5HP compressor.  The starting load never goes over the maximum running load.


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## Karl_T (Jun 2, 2019)

Thanks Jim. You know I lack confidence on wiring on something new.

Creeping elegance. Don't like VFD powered 24x7 so I'm installing a contactor. Pressure switch close contactor. Jumper S1 to comm. 110 to R01A. R01C to air solenoid.

PARTS OF THIS MANUAL MAKE NO SENSE.

I'd like to display current all the time. somebody tell me how. Manual attached.


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## JimDawson (Jun 2, 2019)

Karl_T said:


> Creeping elegance. Don't like VFD powered 24x7 so I'm installing a contactor. Pressure switch close contactor. Jumper S1 to comm. 110 to R01A. R01C to air solenoid.



A contactor is not the best way to start the system, while it works, it is my opinion it will shorten the life of your VFD.  I would leave the VFD powered up while in the shop, and connect all of the controls to the control side of the VFD.  Turn off the breaker to the air compressor when you leave the shop if you like. I leave my VFDs powered up all the time.

I have 2 pressure switches on my system, one for normal operation the other as a high pressure limit.  (in addition to the normal tank popoff valves for over pressure)

I'm a little confused by your wiring description, maybe a quick diagram would be helpful, a picture of a pencil drawing would do

As near as I can tell, you need to set 7.06, bit 4 =1 to display current.


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## Karl_T (Jun 2, 2019)

Well, I'll for sure leave it as is if you think its best to leave the VFD on. Don't need more work for no gain.

I ain't no EE, my attempt at ladder logic below.

The current value of P07.06 is 07FF and it displays frequency of drive. its got to be a hexadecimal number. maybe I should try 1000 base 2 in hex???  Or 8???  I do not see how the current default value relates. The manual sort of implies hex, but maybe I'm over thinking it. I will try 8 in the morning and report back.


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## JimDawson (Jun 2, 2019)

We're missing something here.  How are you telling the VFD to run the motor?  The pressure switch should be connected between S1 and COM I think.  The output relay should only switch the valve.


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## Karl_T (Jun 2, 2019)

sorry, did not include that. A separate pressure switch contact goes between comm and S1.  its at 24 volt


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## john.k (Jun 2, 2019)

You should also consider most systems dont like a start more frequently than every so often...........say 5 or 10 minutes.,so dont set the pressure differential too close.


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## JimDawson (Jun 2, 2019)

Karl_T said:


> sorry, did not include that. A separate pressure switch contact goes between comm and S1.  its at 24 volt




Ah, OK.


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## Karl_T (Jun 3, 2019)

OK changed P7.06 to 8. I get a number that ramps up to 219 as the speed increases, then stays there.  An amp probe ramps to about 21 amps at low pressure then builds to 25 near cutout. I have little confidence that this is a true amp readout, not sure what I got. FWIW, readout displays 60 when off. I assume this is the Hz setting.

Got an edict from SWMBO. Compressor puts static on her favorite night time radio talk even when off. Its got to go. So, I'm back to contactor to bring in VFD.


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## JimDawson (Jun 3, 2019)

Maybe try a different setting, you should be able to get it to read output amps.  The 219 almost sounds like output voltage.

In that case the contactor is required.  I guess set the VFD to start on power up.


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## Karl_T (Jun 3, 2019)

Ok, almost home.

The display selection is the hex value of the bit you want. Binary 1000 (current) is  10 hex. Put this in and display reads current when running.

Installed a contactor. VFD will not start if S1 contact is closed. It will run if you wait until VFD is ready then close S1. Also it will run if you program the general use output to "ready" and wire from comm to the relay comm and then from the NO contact on to S1.

BUT there is only one general use output. Found out the hard way. I need this for control of the unloader.  I went ahead and set this output to run the unloader and have it working correctly.

Back to the "start run" issue.  I've read the manual inside out. Don't see a way to make VFD start as soon as its powered. Am I missing it?

There is a more complicated solution. There is an "open collector" output option. See pics of drawing and paragraph in the manual on wiring it.  this output can be programmed to fire on "VFD ready". I do not know how to wire this to signal the S1 input.


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## JimDawson (Jun 3, 2019)

There may be a parameter something like Restart on Power Fail.  I have seen that in other VFDs, but not sure about the HY units.


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## Karl_T (Jun 4, 2019)

BINGO, yep P1.14 is restart after power fail. Default is disabled 0. reset it to 1.

Tested a couple cycles. Unloader misbehaved once, worked second time. But its 4 AM so I'll wait and check again when I am more awake.

I am REAL CLOSE to having 140 PSI shop air available on demand. Major improvement for when you need the 3/4 impact to take apart rusted farm equipment.

next task is install second pressure switch. Then  wire it for low or high pressure cutout.

One big job left - shoe horn it into my over crowded shop. It will fit in the corner where my spare parts cabinet sits. Some of that stuff will now have to be stored outside. But I really need to keep a lot of it. So, I am fabricating a cabinet support to go over the compressor and store parts all the way up to the ceiling.


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## Karl_T (Jun 4, 2019)

OK, this is a listing of parameter changes to run a Quincy compressor VFD with an unloader air solenoid

P0.01 1     Remote terminal
P5.01 1     forward run
P0.03 60    max freq 
P0.04 60    U F L 
P0.05 60    L F L 
P0.06 60    ref. freq. 
P0.11 5     AC time 
P0.12 5     DC time 
P1.06 1     coast to stop
P7.06 10    display current when running
P1.14  1    restart after power fail
UNLOADER air solenoid
relay output: R01C(NC) 110 VAC to R01A common
P6.02 14    frequency reached for output


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## Karl_T (Jun 5, 2019)

Can FINALY call this project complete!  Tested it all day long yesterday. WERKS GRATE.

Been a long run. about this two years ago got it at auction for $300. Worked there not when it got home. Like all my projects, work on it a bit, set it down, come back.

Everybody, thanks for all the help.

Jim, that means I'm back to the vectrax  project


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## JimDawson (Jun 5, 2019)




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## mksj (Jun 5, 2019)

I would suggest using a pressure switch with two NO contacts (these are fairly standard items for directly switching 240VAC see attached Square D pressure switch), one NO and goes to the VFD NO of relay output 1 to be used as an unloader solenoid. Set P6.02 = 14 which will close the VFD relay when the VFD is at speed. The second pressure switch NO connects the common of the VFD to multi functional input 1 which will signal a run command to the VFD. Be very sure that you do not cross the pressure switch contacts, so use L1 to T1 for the unloader, L2 to T2 for the VFD run command. I would use a 220/240VAC solenoid NC for the unloader,  they are very low amperage, the one below is about is 0.03A. You need to make sure the solenoid is suitable for the maximum pressure, which I assume is 175 PSI. The VFD output 1 relay is rated at 250VAC/3A, you do not want to use HDO output, use RO1A and RO1C .








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Valve stays close when the coil is de-energized, and it opens when energized. This valve has two holes in the bottom and can be mounted in any position. Armature Tube Material: Brass. 2ACK Series Direct Acting Fast Response Electric Solenoid Valve Specification.



					www.ebay.com
				




So when the pressure switch is activated both pressure switch contacts go to close, the VFD executes a run command from L2 to T2, L1 to T1 is closed but the VFD output relay will not close until the motor is at speed and the solenoid will then close (I assume the start up state of the unloader is NO). When the pressure limit is reached the pressure switch goes to open which turns off the input 1 run command and de energizes the solenoid. Agree with Jim that leave the VFD on during the day or when you want the compressor to be used. You can also add switch in series with input S1 so that when open the VFD will not start. I do this with my compressor contactor as opposed to having a main power disconnect.


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## Karl_T (Jun 5, 2019)

You're late to the party 

I did it as you outlined but SWMBO complained about VFD noise on her radio. So, changed it to have the second pressure switch contact bring in a contactor in front of the VFD. Yep, I used Mcmaster Carr's best air solenoid to get the 150 PSI rating. 

I did have trouble understanding several parts of this manual - no where near as user friendly as the GS2 unit manuals from Automation Direct. I guess Chinglish is not my best subject


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