Mycom screw compressor

Hello.
I’d like to get a piece of advice about my situation. I have at the plant the refrigeration compressor Mycom FM 160. Thing is that the compressor works constantly with load 100% even if it gets signal to unload. The slide valve stays without moving towards unloaded side. All oil channels were inspected during overhaul of the compressor; oil was changed. The unload/ load valves and solenoid coils were replaced. I checked tension on the coils during work- it’s okay. The compressor worked quite well during two days after overhaul but now… by the way, it had started to work without unloading before its repairing.
Moreover, I can see increasing of discharge temperature.
I would appreciate any help and advices about it.
Thanks.

welcome to the forum Andrey 7474.
I don't work on these compressors myself.
But I first suspected that the slide valve seals were passing?
But it drives to full load.
Have you tried using nitrogen to simulate the oil driving the slide one way and then the other.
That would identify a blockage at least.
Cheers Grizzly

Hi Grizzly.
Thanks for replying
I haven't tried to do this procedure with nitrogen. I can say that when the compressor stops it starts to unload but very, very slowly. During assembling I checked its moving by hand (there is a special tool for it). It moved smoothly. I suspect that oil circulation during compressor's work is not right. Perhaps, somewhere the oil's flows across or insufficient if it is possible at all.

Andrew,
Agree with Grizzly, check everything is clear.
There is a stop valve & non return valve in circuit to check, also oil return from unloader cylinder to suction of compressor to check as well.
Did you find any damage to unloader seals when overhauling compressor?
Increse in discharge temperature could be because of compression ratio increase like higher discharge pressure, lower suction pressure,higher oil temperatures, mechanical issues.
We years ago had little success overhauling these machines, reason unknown, thrust bearing failures.
So we don't use them anymore, or if we had to, buy a new one.

Thank you Ranger1. You are right about symptoms with the compressor. We had high oil temperature, noise. We replaced all bearings (radial and thrust) because of damages. The slipper seal on the unloader piston was replaced as well. Seems to me that I've found the solution for part of the problem. I've changed settings compressor's PID controller. the compressor has started to unload/load in auto mode. Unfortunately, this process is not stable enough. Loading and unloading go very fast. there is no stability or permanence. This compressor is almost 10 yo. (We have used it since 2007). Perhaps, it overworked.

Thank you for your attention to my problem.

I usually use screwdriver to check operation of loading and unloading. Push the plunger of capacity solenoid from one side or from another side. Capacity slide should load or unload.
You can slow down the movement of slide by throttling capacity solenoid valves.

Segei,
No can do on this type as not a directional control valve

Sorry my mistake. I didn't work on Mycom screw compressors with embedded capacity control valve.

Hi, andrey7474 :)

welcome to RE forums..

Quote:

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Originally Posted by andrey7474

Thank you Ranger1. You are right about symptoms with the compressor. We had high oil temperature, noise. We replaced all bearings (radial and thrust) because of damages. The slipper seal on the unloader piston was replaced as well. Seems to me that I've found the solution for part of the problem. I've changed settings compressor's PID controller. the compressor has started to unload/load in auto mode. Unfortunately, this process is not stable enough. Loading and unloading go very fast. there is no stability or permanence. This compressor is almost 10 yo. (We have used it since 2007). Perhaps, it overworked.

Thank you for your attention to my problem.

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Can you, please, upload some photo of your capacity regulating valve ... probably within 3-way valve you have regulating valves, both for capacity increase i.e. decrease ... not sure can be different depending on the manufacturer ... very old machines were equipped with 4 single solenoid valves with outside tubing arrangement for oil flow ....

Do not worry about age of your compressor ... with proper maintenance can run next 10+ years ... very good machines ...

Best regards, Josip :)

Hi Josip.
Please, look at photos. Compressor has two 3-way valves. The left one -unload valve, the right - load valve. Attachment 14647Attachment 14648Attachment 14649Attachment 14650
We replaced them both. As I told above, compressor started to unload according its SP but I'm not happy about instability of this process. ( I remember its work 10 years ago :)) I agree with you that this compressor is quite reliable and good machines.

Best regards.

p.s. I uploaded four photos

Hi friends,
when I read all the answers and everything checked and OK, I fear that the problem will guide regulatory position 246, there is a need to overhaul while always change and adjust. when the compressor is not rotating, it is okay to start the compressor, the regulation has the ability to shoot (the control side of the rotor) and is not stable for a shift.

What is your opinion on my answer?
Josef.

Quote:

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Originally Posted by josef

Hi friends,
when I read all the answers and everything checked and OK, I fear that the problem will guide regulatory position 246, there is a need to overhaul while always change and adjust. when the compressor is not rotating, it is okay to start the compressor, the regulation has the ability to shoot (the control side of the rotor) and is not stable for a shift.

What is your opinion on my answer?
Josef.

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Josef,
Agree item 246 which guides slide valve & prevents it from rotating & possibly contacting male rotor.
This, if worn or out of adjustment can cause capacity control issues.
If nut securing unload piston is overtightened can be one reason guide can be out of adjustment.
Only one valve on capacity control, as well as a non return valve which if leaking, can also cause issues.

Without knowing exact condition of compressor & it's components we can only speculate I guess.
Would also be nice to know if a continuous load or unload pulse will move slide valve, maybe pulse times can be adjusted if controller can work that way.

RANGER1,
I agree, and backflow preventer is important. Many engineers believe that the overhaul of the screw compressor is an exchange bearings-wrong, every part of the compressor has its justification and purpose.

Josef and RANGER1. I can say that item 246( according to exploded view of parts) or unloader slide valve without any damages or worn. The male rotor in a good shape. the overhaul of compressor was made a few days ago. all torque moments are ok.( according to manual). RANGER1 mentioned about continuous pulses. I was trying to change it but i can't find the correct value. it becomes or too fast or too slow. unfortunately, we don't have any opportunity to get access to settings of PID controller into PLC and I don't have opportunity to see a curve of PID controller.

what could you advise to do?

Best regards

Andrey

Andrey,
not must be no wear, there must be a fit and adjustment. But after every 25,000 hours of operation change-why manufacturers recommend Mycom ??

Josef.

I'm sorry Josef. what did you mean when you asked about recommending Mycom?
of course, a small wear is available but I meant that I didn't find any traces of touching between m/rotor and slide valve during observing.

by the way, I can upload a video of the screen of OP where you can see all parameters of the compressor's work.

Andrey

Andrey,
touching the slide and the rotor is already late, but your problem is not rotor and a slide, slide your problem that is not working properly there valve guide which may be your problem.

Josef.

oh, I see. Thank you Josef. I understand now what you mean. I've just looked at scheme.
Thank you very much. I will need to check it.

Best regards

Andrey.

Good luck.
And remember, please report what the result, too many people who are trying to help you.

Josef.

Thank you for helping. I will report about the results but I can't promise that it will happen soon. It depends on many things and circumstances. Anyway, I will do it.

Best regards.

Andrey.

Andrey,
i understand a lot of the work will be.
Therefore, good luck.

Josef.