Liquid ammonia injection for cooling.

[mrsparky]

Please excuse my terminology for I come from an electrical background. We have one ammonia compressor that the motor has a hard time starting. The compressor inertial load seems to be greater than designed for the motor. The motor, compressor bearings and slide valve can be eliminated for this problem due to extensive troubleshooting.

The compressor is stopped now and has been off for a couple of days. The liquid ammonia injection for compressor cooling is frosted up. None of the other shut off compressors is displaying any frosting up and are in fact ambient room temperature.

The piping: First is a shut off valve then a check valve then a solenoid then a window then a regulator then shut off valve and then compressor entry. There is heavy frost at the window and between the solenoid and regulator.

I do not believe this frost should be there since the compressor is turned off and not requiring any cooling. Is it possible that liquid ammonia is being injected into the compressor when off thus causing the motor to see a heavy load during start. The motor only sees a too heavy of a load during start and not run. Any ideas of what is going on here? Also, what should one see in the window when the compressor is off or when the compressor is on. Thank you for any and all responses.

[Andy]

Please excuse my terminology for I come from an electrical background. We have one ammonia compressor that the motor has a hard time starting. The compressor inertial load seems to be greater than designed for the motor. The motor, compressor bearings and slide valve can be eliminated for this problem due to extensive troubleshooting.

The compressor is stopped now and has been off for a couple of days. The liquid ammonia injection for compressor cooling is frosted up. None of the other shut off compressors is displaying any frosting up and are in fact ambient room temperature.

The piping: First is a shut off valve then a check valve then a solenoid then a window then a regulator then shut off valve and then compressor entry. There is heavy frost at the window and between the solenoid and regulator.

I do not believe this frost should be there since the compressor is turned off and not requiring any cooling. Is it possible that liquid ammonia is being injected into the compressor when off thus causing the motor to see a heavy load during start. The motor only sees a too heavy of a load during start and not run. Any ideas of what is going on here? Also, what should one see in the window when the compressor is off or when the compressor is on. Thank you for any and all responses.

Hi Mrsparky

Yes your liquid injection solinoide is passing To prove this take the compressor off auto start and leave it off with the shut off valve to the liquid injection solinoide shut. When you want to stsrt the compressor put it back on auto start. When the compressor has started again open the liquid injection feed shut-off valve

Ammonia causes erosion of the solinoide valve seats by an effect called wire drawing. You could change the valve to a Danfoss AKV which has a peak type plastic used on the static part of the seat and the usual teflon on the slug that moves in the valve when energised.

Danfoss have some new valves available based on the ICM module, these are discussed earlier in this tread.

Happy fault finding

Kind Regards Andy

[NH3LVR]

The piping: First is a shut off valve then a check valve then a solenoid then a window then a regulator then shut off valve and then compressor entry. There is heavy frost at the window and between the solenoid and regulator.

Welcome to the Forum Mrsparky!
Andy, as always is correct.
I am very concerned about the piping arrangement you describe. If indeed you have a check valve before the Solenoid, it could lead to a dangerous situation.
I believe it is most likely a bit different than your description. Or I may be not understand you correctly.

If this is an American built package, you most likely have a Sporlan Solenoid for the liquid injection. They do fail and I have replaced many of them for that reason.
The biggest problem here is if the machine is full of liquid. This could be very dangerous if you are able to get it started.
Do you have a local mechanic familiar with these? If so I would encourage you to contact them.
Judging from the time of morning this post was made I think you may be in a breakdown situation.
Send me a private message and I may be able to be of help to you.

[US Iceman]

FIrst of all welcome to the RE forums mrsparky.

None of the other shut off compressors is displaying any frosting up and are in fact ambient room temperature.

This what you should be seeing on the problem compressor also. It certainly sounds as if the solenoid valve is leaking. Are you sure it's not energized when the compressor motor is OFF?

What is the oil separator sump temperature at start-up?

Do the separator site glasses have a lot of foaming in them during start-up?

[Josip]

Hi, Mrsparky

Welcome to RE

The compressor is stopped now and has been off for a couple of days. The liquid ammonia injection for compressor cooling is frosted up. None of the other shut off compressors is displaying any frosting up and are in fact ambient room temperature.

The piping: First is a shut off valve then a check valve then a solenoid then a window then a regulator then shut off valve and then compressor entry. There is heavy frost at the window and between the solenoid and regulator.

Well, your solenoid valve is damaged and there you have a leak (frost after solenoid valve till compressor entry) even your compressor is colder (you can check it with infrared thermometer) and you must replace solenoid valve with new one as per Andy's advice.

I do not believe this frost should be there since the compressor is turned off and not requiring any cooling. Is it possible that liquid ammonia is being injected into the compressor when off thus causing the motor to see a heavy load during start

Even when compressor is off there is suction pressure within due to equalizing hole in suction check valve. Ammonia for cooling is under condensing pressure and easily can be injected into compressor under suction pressure and partially evaporate and partially remain in oil causing a lot of foam and reduced lubrication during run. But before that with very cold and dense (sticky) oil it is not easy to start compressor.

Best regards, Josip

[NH3LVR]

I have asked Mr Sparky to PM me.
I was not trying to short circuit the Forum, but wanting to get more detail for us to discuss.
It is not uncommon for a small leak in the Solenoid to be present for sometime before it is noticed or causes a problem.
However I am really concerned about the heavy load at startup. It may well be a Electrical problem, but I fear for his safety if the screw is full of Liquid.
All of us could determine this quite easily. But his limited experience with Compressors leaves me feeling very nervous.
I do respect his willingness to tackle this problem.

[Josip]

Hi, NH3LVR

I have asked Mr Sparky to PM me.
I was not trying to short circuit the Forum, but wanting to get more detail for us to discuss.
It is not uncommon for a small leak in the Solenoid to be present for sometime before it is noticed or causes a problem.
However I am really concerned about the heavy load at startup. It may well be a Electrical problem, but I fear for his safety if the screw is full of Liquid.
All of us could determine this quite easily. But his limited experience with Compressors leaves me feeling very nervous.
I do respect his willingness to tackle this problem.

Here in my country in one company they run compressor for almost 2 years with leaking injection solenoid valve. Sometimes compressor was frozen completely . Nobody ask for service .

Call for service was to change shaft seal, oil filter and oil with complete check. Rotating compressor by hands there was some resistance and advice was to open and check screws. Found all Ok. Bearings must be replaced no way to check them.

Finally small leak cost as complete overhaul (change of complete set of bearings) SAB 163.

Best regards, Josip

[mrsparky]

I am at home now and tried a "quick reply" but it did not go through so if my post response gets doubled that is the reason.

Thanks all for the inputs. I suspected the solenoid but our experienced refrigeration man is out on sick leave.

I will try and answer all of your questions:
1.) I suspected the soleniod but have not yet checked for energization voltage when the compressor is off. I will do this at the next opportunity.
2.) The pipe fitting just before the solenoid may indeed be a strainer rather than a check valve.
3.) I am sure that the oil is up to temp before start.
4.) I am 99.999% positive that the problem is not electrial.

This has been an on going problem with this compressor for at least two years. The motor groans loudly while in star that only stops once it switches to delta and comes up to speed. The same problem showed up with different motors. The refrigeration man warned me about liquid ammonia in the compressor screw and what can happen. I will check for solenoid energization voltage and if absent will ask refrigeration to order a new solenoid of the type that Andy mentioned. Thanks again, Robert

[US Iceman]

And we wonder why ammonia gets a bad rap!!!!!

I'm sure you have seen this type of maintenance practice before. It's very common in HVAC and commercial refrigeration systems. Unfortunately, it is also getting to be more common in industrial refrigeration too.

Too many accountant types thinking they are saving money!

[US Iceman]

The motor groans loudly while in star that only stops once it switches to delta and comes up to speed.

Are you also sure the slide valve is all the way unloaded before the compressor tries to start?

One more question... Are the other compressors wye-delta start also? no problems on them I assume?

[mrsparky]

Since we have solved the other problem I would like to ask one more that I am curious about. We have two new compressors for flash freezing at a new freezer. The booster for the extreamly low temperatures has had several problems. It burned up its motor connections in the peckerhead and also had a bad oil level sensor. These problems were repaired. What I am curious about is that in the upper window of the oil separater tank, sometimes I see foaming and sometimes I don't. I only see the foaming on the booster low temp compressor and not any of our other regular compressors. What would cause the foaming to appear in the upper window and then to disappear. I woud say that an hour or two is enough to cause this reversal. Again thank you, Robert

[mrsparky]

In answer to US Iceman, It was proven that the slide valve is working correctly. Our compressors are all star/delta start except for one I am currently changing to soft start and the two new ones I talked about in my last post. I convinced the boss to change to soft start after reading and communicating with an electrical engineering forum.

[US Iceman]

It burned up its motor connections in the peckerhead...

What caused this? Were the split-bolt connectors loose, or did the insulation pads chafe against the peckerhead?

By the way, it's been a long time since I heard anyone use the term peckerhead. If someone has not heard of this before, they might think you are calling them names!

What would cause the foaming to appear in the upper window and then to disappear.

It could be caused by cool oil at start-up, or some liquid refrigerant getting into the oil during pull down.

Does this occur only at certain times?

And, when the oil is foaming...what's the discharge temperature?

[nh3wizard]

Is the machine liquid injected also? Could be overfeeding

[mrsparky]

The reason for the motor connection to burn up in the peckerhead was the "extra flex steel" motor taps locked down in a connection block. The electrical engineering forum advised a "stud block". With all the "political correctness" I should have said motor junction box but that was the term I was taught.

[US Iceman]

With all the "political correctness" I should have said motor junction box but that was the term I was taught.

It's the term I was taught also. It seems ever time I have used it, everyone just looks at me funny.

My comment was not meant to enforce political correctness, but only to highlight a term most may not be familiar with.

[Josip]

Hi, Mrsparky

Are you also sure the slide valve is all the way unloaded before the compressor tries to start?

In answer to US Iceman, It was proven that the slide valve is working correctly. Our compressors are all star/delta start except for one I am currently changing to soft start and the two new ones I talked about in my last post. I convinced the boss to change to soft start after reading and communicating with an electrical engineering forum.

Before compressor start slide valve must be in minimum position, but that does not mean during inrush there is no movement of slide valve toward max position causing heavy load to electric motor.

Sometimes this happened with Stal screw compressors due to some problems with unload/load solenoid valves or check valves or relief valve. It is not common but sh*t happens .

I'm sorry we are speaking about some problems but still not know anything about your compressors (all screws are almost the same but not exactly )

Please can you tell us something about?

It's the term I was taught also. It seems ever time I have used it, everyone just looks at me funny.

Regarding "peckerhead" in Webster's dictionary found only "pecker" - no need to say anything more

What I am curious about is that in the upper window of the oil separater tank, sometimes I see foaming and sometimes I don't. I only see the foaming on the booster low temp compressor and not any of our other regular compressors. What would cause the foaming to appear in the upper window and then to disappear. I woud say that an hour or two is enough to cause this reversal.

It is normal to see some foam due to injection cooling. If there is not any change in oil pressure and compressor's sound no problem. Maybe to see is it possible to reduce amount of injected ammonia even if oil temperature rise a little.

Best regards, Josip

[Andy]

Since we have solved the other problem I would like to ask one more that I am curious about. We have two new compressors for flash freezing at a new freezer. The booster for the extreamly low temperatures has had several problems. It burned up its motor connections in the peckerhead and also had a bad oil level sensor. These problems were repaired. What I am curious about is that in the upper window of the oil separater tank, sometimes I see foaming and sometimes I don't. I only see the foaming on the booster low temp compressor and not any of our other regular compressors. What would cause the foaming to appear in the upper window and then to disappear. I woud say that an hour or two is enough to cause this reversal. Again thank you, Robert

Hi Robert

Oil foaming is very common can be a whole host of things

Oil too warm

Oil with large quantities of refrigerant traped in it boiling off

The design of the oil separator, lots of inpingment

The selection of the oil separator, in particular low temperature compressors during pulldown (the oil separator size when the suction pressure is up needs to be bigger than when at or near design temperature)

As Josip and NH3 Wizard indicates, an over injecting injection system is another possibility.


The best cure for liquid injection problems, is none. Use a refrigerant(thermosyphon) or water cooled oil cooler instead.
The water cooled oil coller can be used to preheat boiler water or factory wash down water, saving money. Your compressors will have addtional capacity and in effect (with high stage directly or low stage indirectly) you will be increasing the size of the system condensers

Kind Regards Andy

[mrsparky]

Thank you for the informative comments. On any future installations I can make reccomendations about compressor cooling. I already knew from glancing at literature that liquid injection is not as efficient.

In re to US Iceman and Josip. The reason I know the slide valve is at minimum position at start is that the dial indicator is pointing to zero. The refrigeration man had shown me in the past how the dial indicator is connected mechanically to the slide valve so for it to indicate zero the slide valve must be at minimum. Please correct me if I am wrong.

In re to Josip, inrush has a different meaning in the electrical world. Are you talking about the inrush of gas?

[Josip]

Thank you for the informative comments. On any future installations I can make reccomendations about compressor cooling. I already knew from glancing at literature that liquid injection is not as efficient.

In re to US Iceman and Josip. The reason I know the slide valve is at minimum position at start is that the dial indicator is pointing to zero. The refrigeration man had shown me in the past how the dial indicator is connected mechanically to the slide valve so for it to indicate zero the slide valve must be at minimum. Please correct me if I am wrong.

In re to Josip, inrush has a different meaning in the electrical world. Are you talking about the inrush of gas?

Slide valve must be at zero position otherwise you have not starting permission, but that not prove there is not any slide valve move during start time.

Due to my, not so good, english, here inrush has meaning from the moment when we push start button (we are in star -with very high amperes-low speed, waiting couple of seconds from 3-4 up to 10-12 (usually 7-8) coming to nominal speed and reduced amperes til here, then switch to delta.

No need to say that good electrical motors coming to nominal speed within 1,5 sec after start with star/delta combination.

Best regards, Josip

[US Iceman]

The refrigeration man had shown me in the past how the dial indicator is connected mechanically to the slide valve so for it to indicate zero the slide valve must be at minimum.

That's quite true, as long as the mechanism is adjusted and claibrated properly.

If for some reason the slide valve is partially loaded, the inrush current will be dramatically higher and the motor could stall, especially with wye-delta.

My questions come from one of your earlier comments about several motors being tried and that was not the problem.

This has been an on going problem with this compressor for at least two years. The motor groans loudly while in star that only stops once it switches to delta and comes up to speed. The same problem showed up with different motors.

Therefore, if you have tried changing motors with the same end result, I would tend to want to absolutley rule out anything with the compressor.

[mrsparky]

This thread has certainly grown in length and I appreciate the interest it has generated.

My original thought was the leaking liquid injection solenoid with the subsequent ammonia wet screw is the source of the hard starts. The test suggested by Andy should prove if the leaking solenoid is causing this problem. At the least, repairing the leaking solenoid will make for a safer installation.

If the hard start problem still persists, then if the slide valve is wandering during start would not the dial indicator give me a visual test? As long as it stayed zero would it not be at minimum? I have watched the slide valve dial indicator during start and it remains at zero. The refrigeration assured me in the past that the slide valve is adjusted for minimum when the dial indicator points to zero.

I also thought about the check valve after the compressor discharge but if I remember correctly (I am still at home because of the holiday), there is a gas pressure gauge located before it and it did not show an abnormal reading. If the solenoid is not the source of the hard start then I am out of ideas again. The refrigeration man and I am at an impasse because he maintains that the screw is not the problem and I have proven that electrical is not the problem. I have probably missed some suggestions from other posts on this thread and will read it all carefully again if the injection solenoid is not the problem. Thanks, Robert

[Josip]

Hi, Robert

If the hard start problem still persists, .........................

The refrigeration man and I am at an impasse because he maintains that the screw is not the problem and I have proven that electrical is not the problem. I have probably missed some suggestions from other posts on this thread and will read it all carefully again if the injection solenoid is not the problem. Thanks, Robert

There is one more possible test. Remove coupling and then start your motor without compressor (it will run at least for 30-60 seconds without any jumper. Check amperes, noise...

Also try to rotate compressor by hands is it hard or smooth.

Another possibility (not easy) to install another motor (if available-seems it is) to that compressor and then try to run it. I did not understand from your posts if you already did that.

Anyhow still no information about type of compressor,.....etc

Best regards, Josip

[NH3LVR]

Mr Sparky;
It occurred to me that the first test might be the simplest.
Disconnect the coupling between the Compressor and Motor and attempt to start the Compressor.
If the hard starting is caused by a poor contact it might start anyway under the reduced load. But it is a simple test that is easily accomplished.

[US Iceman]

The refrigeration man and I am at an impasse because he maintains that the screw is not the problem and I have proven that electrical is not the problem.

Something is not right.

What kind of screw compressor is it?

You mentioned the discharge check valve and the pressure upstream of the valve. There should be a bypass of some sort on the suction check valve. Sometimes a hole is drilled in the check valve, most of the time there is a bleed line around the check valve.

The purpose of this equalizing or bleeding to suction pressure is to reduce the pressure the compressor is starting against.

[NH3LVR]

I have never had a problem starting a Screw against head pressure. That is not to say it could not be a problem in some cases, but when it starts the pressure is equal on both sides. The Suction pressure is measured upstream of the suction check valve. The compressor equalizes quite quickly when it is shut off.
It would be of great help if Mr Sparky would tell us which Screw Package he has.

[mrsparky]

If it is an electrical problem with the hard start, the installed motor would have to have a defective squirrel cage rotor and the spare motor would have to have exactly the same problem. These are both re-wound motors probably more than once. While this is a probability it is highly unlikely.

The uncoupled motor displays no problems with start and run. Only when it is coupled to the compressor does the groaning occur. I have taken RPM measurements during start and compared to a working system. My RPM meter is slow to read out but the RPM for the defective system is lower than a working system at transition to delta. Increasing the transistion time has only the negative effect of keeping the motor at high amps longer than it should.

The electrical side of this problem has been hashed out in an electrical engineering forum some time ago and unless the rotor is spun then the problem lies with the compressor. This is why I am seeking guidance in this refrigeration forum.

I think it is an FES compressor but I seem to remember seeing the word "Hartford" or something like that on the manufacturers name plate. I don't know the size of the compressor but the motor is 500HP and this compressor is being used for high stage and not booster.

[US Iceman]

It could be an FES package with a Hartford compressor on the package. Hartford compressors ar ethe old Dunham-Bush screws.

My RPM meter is slow to read out but the RPM for the defective system is lower than a working system at transition to delta.

How much lower is the RPM on the problem compresssor. What you are describing sounds like a stall condition.

Has any checked the speed-torque curves for the compressor and motor yet? The motor may be perfectly fine, but it may not develop sufficient torque during start-up. I've seen this happen on a brand new motors (several of them in fact).

We are going on a little bit of a witch hunt here, but we do not have access to the compressor or anything else, so please be patient with us.

[mrsparky]

I forgot to address one other issue previously mentioned. The motor is coupled to the compressor now and I will not be able to perform the following test in the near future. I seem to recall from earlier tests that the compressor shaft will turn by hand but it takes some muscle. How much force should be needed to turn a uncoupled compressor shaft?

[mrsparky]

I am pulling from an old memory board (my head) for the RPM data. All of our star/delta compressors have a factory (RAM Co.) transition time of 6 seconds. The RPM in a working system is app. 1/2 of motor data plate RPM after 6 seconds. So the RPM is around 1600 RPM in a working system at transition. Increasing transition time does not significantly increase star RPM at transition to delta. In the defective system the RPM is app. 1200 at transition. I would have to check my records for more accurate data.

I will add that the working system transition to delta at 1/2 data plate RPM surprized many electrial engineers who maintained that the star configuration should be close to data plate RPM at transition. This arguement was discounted by observing many other working systems.

[NH3LVR]

It should take very little force to turn the Compressor by hand. They are a bit sticky after sitting for a bit. But after you get it to turn you should be able to turn it by hand with a little bit of leverage. The motor should not add anything appreciable except inertia when attempting this. It should turn without any binding. Have you checked the end play?
I am suspecting a problem in the starter. It sounds like it almost, but not quite single phasing. I may be wrong, but a connection or contact could be breaking down under the higher Amperage when the motor is coupled to the compressor.
If it is an FES machine it will say so on the control panel, or at least have an FES contract number on the inside of the door. Share that information with us, if you would.
The one reason I doubt you have a compressor problem is that it would most likely failed in the length of time you have had the problem, if it was mechanical.

[mrsparky]

In re NH3LVR, The compressor shaft did not turn freely by hand when uncoupled from the motor, if memory serves me correctly. I remember wondering if there was enough oil on the screws or if they were to tightly bound. As I mentioned earlier, once up to speed the compressor performs like the other compressors, although I think it pulls 5%-10% more amps. than the other compressors at different slide valve positions.

I take it from the posts that the consensus must be that the leaking ammonia cooling injection solenoid is not causing my hard start.

Please believe me when I say there is nothing wrong with the electrical side except maybe (very slim possibility) we have two motors with rotors spun the same way. A couple of years ago we even bought a brand new motor for this compressor. Luck had it that another compressor had a motor go bad when the new motor arrived so it got the new motor. All this compressor has seen during my employment is re-wound motors, that the re-wind shop say are good.

[NH3LVR]

This is turning into quite a mystery!
I do have one thought, a little far, out but bear with me.
I am wondering if there could be a problem with the compressor suction check valve, or the bypass around the check being open too far. This will cause the oil to move back up the suction line on shut down. It would work it's way back down over time, but could cause a problem in starting.
I have seen it happen before, although the only symptom I noticed at the time was a loud noise on startup.

[mrsparky]

In re NH3VLR, The last symptoms you talked about are exactly what I am witnessing during start. It would satisfy my contention that the electrical is in good shape and the experienced refrigeration mechanic that the compressor is in good shape.

Is there a simplified way for an electrician to check the condition of the suction check valve and the bypass around it? The refrigeration man is supposed to be back this coming week and I will go over this thread with him to try and find a solution.

[NH3LVR]

Is there a simplified way for an electrician to check the condition of the suction check valve and the bypass around it?

I cannot be too specific without know which panel you have, but here are the basics.
Remember first that the suction pressure indicated on the panel is measured in the suction line upstream of the suction check valve-not the pressure inside the machine itself.
After the machine has been sitting for awhile the discharge pressure indicated on the compressor (not on a discharge gauge somewhere else in the system) should have come down to suction pressure.
If it has not you do not have a problem with the suction check-you have a different problem, so do not continue.
Start the machine and let it run until it is up to temperature. Note the oil level.
Shut the machine off. Watch to see how quickly the indicated suction pressure falls off. Normally this will take at least twenty minutes or more. If the check valve is defective it will fall very rapidly. If the bypass around the check is open too far it will fall but not as rapidly.
Also watch the oil level. If it goes down very quickly after shut down it may indicate the oil is going back into the compressor.
This is a simple explanation. The results of this test are subject to interpretation. I would not encourage you to hastily make adjustments. The bypass valve I am talking about is very easy to confuse with all the other small valves on the machine.
A failed suction check can cause oil loss after shutdown, but it may not happen in your case. If the suction line is of a sufficient length before it goes into the suction header it may well not go back into the system, but sit above the machine waiting for the next start. How long it will stay there before going back into the machine is a question I do not have the answer to.
Again do not be too hasty to try to make adjustments.
NH3LVR

Good Luck

[US Iceman]

If the suction line is of a sufficient length before it goes into the suction header it may well not go back into the system, but sit above the machine waiting for the next start.

That's another possibility. If the oil is sitting in the suction line, it could be similar to a flooded start which does cause higher than normal current draw.

I would also agree with the comments about not adjusting anything. Strongly agree in fact. This is what usually happens when troubles appear. All sorts of adjustments are made, and finally someone finds the problem after a lot of guessing.

It's less trouble to try to spend the time solving the problem, than it is to correct all of the changes performed. This is like someone wanting to adjust superheat on TXV's at the first sigh of a perceived problem. It's almost always the wrong thing to do.

[Josip]

Something is not right.

For sure!

We still do not know all about compressor and electric motor, i.e. complete unit history, just thinking out loud...

Have feeling we all wandering around like blind chickens trying to find corn seed...

...reading all posts couple of times I cannot put away that there is some problem with electric motor. This big noise and decrease of rotation during inrush shows that motor torque is just above needed for that compressor .

N.B. I had a problem with 5 Stal screws where we had to evacuate complete unit down to suction pressure to make start, otherwise there was the same story what we have here. There was not bypass valve installed. (This was a good school for all of us for another plant where we installed those valves to solve the same problem.)

Problem persist from early beginning due to ignorance of electrical engineer because he ordered electrical motors like 3000 rpm/250kW. Later on, speaking with electrical engineers from Stal, I found out there is a list with about 40+ points of data needed to choose the right motor. As I am not el. engineer that is a Science Fiction for me

What can cause that:

1. motor maybe was not good from early beginning

2. motor was rewind....

3. If there is a bypass valve which must be open during inrush it is possible that one is not working properly due to mechanical malfunction or burned coil thus no internal leaking for easy start.

4. Problem regarding oil is also possible but then there should be a squeezing sound...

Maybe I am not right, but this is my experience and just hope to help.

One more question is that maybe 2 speed motor???

Best regards, Josip

[Andy]

[QUOTE=mrsparky;57918] valve positions.

I take it from the posts that the consensus must be that the leaking ammonia cooling injection solenoid is not causing my hard start.
QUOTE]

I would say that an injection valve fault is your most likly fault.

Frosting accross the valve whilst off.

Compressor hard to turnover by hand.

What else could it be

Kind Regards Andy

[US Iceman]

Have feeling we all wandering around like blind chickens trying to find corn seed...

That's my feeling too. I don't want to start a finger pointing contest, but this problem does not pass the "smell test".

Later on, speaking with electrical engineers from Stal, I found out there is a list with about 40+ points of data needed to choose the right motor.

I have seen something like this sheet before also. A motor is not just a motor. This is why I mentioned the speed-torque curves earlier.

mrsparky, have you contacted FES yet? They should be able to help you.

[mrsparky]

The holiday is over and I am back on my third shift at work and I saw the experienced refrigeration mans car in the parking lot. We should now be able to tackle this thing in earnest. I'll get back after a little while.

[US Iceman]

I have some more questions... does the wye-delta starter have an open or closed transition?

One last one; you mentioned the problem had been going on for about 2 years. What changed two years ago?

[mrsparky]

Two years ago I became the de facto ammonia electrician. Eight years ago when I hired on this compressor was down and being worked on and has been a pain ever since. All of our star/delta starters are closed transition. I spoke to the refrigeration man about the injection solenoid. After feeling it he agrees that it needs replaced and that we have a box full of new ones. I will replace this solenoid after I take care of my other plant duties.

I looked at the slide valve dial indicator and it is pointing at 4% while the compressor is off. I will pay close attention to this after the solenoid is replaced. The way things work around here it may be a day or two before I have anything to report about the progress being made. I will provide feedback as things unfold. Thanks again to all. Robert

[mrsparky]

Replaced the injection solenoid and now the motor is quieter during start.

[Josip]

Hi, Robert

valve positions.

I take it from the posts that the consensus must be that the leaking ammonia cooling injection solenoid is not causing my hard start.

It certainly sounds as if the solenoid valve is leaking.

Well, your solenoid valve is damaged and there you have a leak (frost after solenoid valve till compressor entry) even your compressor is colder (you can check it with infrared thermometer) and you must replace solenoid valve with new one as per Andy's advice.

I would say that an injection valve fault is your most likly fault.
Frosting accross the valve whilst off.
Compressor hard to turnover by hand.
What else could it be

Kind Regards Andy

Replaced the injection solenoid and now the motor is quieter during start.

Best regards, Josip

[nh3wizard]

Does the solenoid have a set point for the Oil temp?
If so what is it?

[karelsdr]

We all agree that your solenoid is leaking by. But if it is frosting after being off for a few days , it is not a big leak and is not your starting problem.To get the frosting only at the valve means your oil sump heaters are boiling off the liquid in the serarator. It is possible your motor has been sized at full load running conditions(e.g. -20 deg evap and 95 degree con) If this is the case you need to throttle the suction valve from near closed to start. Then check your oil sump for frosting and oil temp. Any abnormal noises just shut if off and reasses

[US Iceman]

Hi karelsdr,

Welcome to the discussion. You raise a good point about the liquid injection solenoid. I'm not convinced the replacement of the solenoid valve solved the underlying problem.

It may have minimized the problem to an extent that the compressor now starts without any perceived problems.

I think it would be prudent to continue to check into the details more to ensure everything is OK. As I said before, something about this does not pass my smell test.

Wye-Delta starters on large motors can be fickle. Since you only have 33% of the current, the starting torque developed by the motor is also lower. Any amount of voltage imbalance can also reduce this and also increase the motor winding temperatures.

It would be interesting to see any motor teardown report that might have been done.

[karelsdr]

How much time from the wye contactor to the delta contactor

[US Iceman]

I think six seconds was the value set for the transition timer. For some reason I want to say the value I remember being told to set this should be around 3-4 seconds on a Westinghouse starter many years ago.

[mrsparky]

in re nh3wizard, quote the experienced refrigeration mechanic, "The solenoid on this machine does not control oil temperature. The solenoid comes on when the machine starts and turns off when the machine stops. Oil temperature is controled by the thermo expansion valve that is set to 70-80PSI and this gives you an oil temperature of 125-130 degrees F."

in re karlsdr, all of our star/delta starters transition time is factory default to 6 seconds.

in re US Iceman, take my word for it there is nothing wrong with the electrical side of the machine unless the installed re-built motor has a spun out rotor and the spare has a spun out rotor in exactly the same manner. While this is a possibility it is highly unlikely. Unless the motor re-wind experts are incompetant, again highly unlikely.

The loud noise during start has been significantly reduced after the injection solenoid replacement. I will explore the earlier post from karelsdr with the experienced refrigeration mechanic about the suction valve after he gets back down from the roof.