compact screw oil carry over

[l2embo]

Hi
I am having oil carry over problem with a Refcomp compact screw model SRC-S-133 which works on -20/+35 degree centigrade temperatures.
I counted on internally designed oil separator but after commissioning we found out there are excessive oil carry over from the compressor.
at the next step we used an oil separator with oil return to suction side of the compressor (regarding that there isn't any other recommended port for that) although the carry over rate has been decreased but still stands and cause to shut down after a few days of working.
I have also attached some photos to help find the problem please.
any suggestion?
155f18bd-f157-4414-8c2b-77623b48e5b8.jpg
099264a0-4e7f-4c6a-9612-8df0c40a4a42.jpg
ebd7fd52-5587-4de7-8bf0-8af4fc947a26.jpg

[RANGER1]

12embo,
Need more information to help.

1/ What type of evaporator do you have, can it collect oil ?
Need to know where oil is collecting.
2/ Evaporator superheat
3/ Type of refrigerant & oil.
4/ Was oil separator sizes for the load, or pipe sizes?
5/ Does oil in sump foam all the time?
6/ Discharges temperature.
7/ Is oil return definitely returning.


Usually after oil separator is sized for maximum load & is coalescer replaceable filter type like Temprite.
Oil is collecting somewhere & that will decrease evaporator performance & possibly flood back.

[l2embo]

Hi RANGER1
1. Evaporator is a flooded flake ice drum ( with surge drum ) with an oil trap at the bottom of it and an oil drain valve. we regularly open and drain the oil which carried from the system. The oil is very dirty and not usable.
2.Evaporator superheat is 5 degree centigrade
3. The oil is suniso 4GS and refrigerant is R22
4. Oil separator pipe size and discharge line size are the same. Usually for screw compressors we use bigger oil separator than you can see in the picture but since the catalog doesn't mention any possibilities for using an external oil separator we use this.
5. Yes, the oil almost always foam in sight glass.
6. Discharge temperature is about 90 degree centigrade and discharge pressure is 150-165 psi.
7. We are mostly sure that the oil return from oil separator. but there is a doubt that oil could possibly migrate into 3 meter vertical suction line and to the surge drum because of the pressure difference. ( discharge pressure 150/suction pressure 25 psi) there is no connection embedded for the oil return so we used suction connection for that. there are also doubt for using oil cooler route for oil return which we again worries of oil wrong direction passage from oil cooler to oil separator due to little pressure difference.

The other point is that when we reduce the capacity from 100 to 75 and so on the oil foam will return in sight glass more.

this is the link for the instruction manual for this compressor for your reference. https://www.hosbv.com/data/specifica...HandBook_E.pdf
your advises would be precious for me.
Regards

[RANGER1]

Hi RANGER1
1. Evaporator is a flooded flake ice drum ( with surge drum ) with an oil trap at the bottom of it and an oil drain valve. we regularly open and drain the oil which carried from the system. The oil is very dirty and not usable.
2.Evaporator superheat is 5 degree centigrade
3. The oil is suniso 4GS and refrigerant is R22
4. Oil separator pipe size and discharge line size are the same. Usually for screw compressors we use bigger oil separator than you can see in the picture but since the catalog doesn't mention any possibilities for using an external oil separator we use this.
5. Yes, the oil almost always foam in sight glass.
6. Discharge temperature is about 90 degree centigrade and discharge pressure is 150-165 psi.
7. We are mostly sure that the oil return from oil separator. but there is a doubt that oil could possibly migrate into 3 meter vertical suction line and to the surge drum because of the pressure difference. ( discharge pressure 150/suction pressure 25 psi) there is no connection embedded for the oil return so we used suction connection for that. there are also doubt for using oil cooler route for oil return which we again worries of oil wrong direction passage from oil cooler to oil separator due to little pressure difference.

The other point is that when we reduce the capacity from 100 to 75 and so on the oil foam will return in sight glass more.

this is the link for the instruction manual for this compressor for your reference. https://www.hosbv.com/data/specifica...HandBook_E.pdf
your advises would be precious for me.
Regards

Originally you say you were draining oil from ice machine & was very dirty?
Now you get nothing.
You can return oil from evaporator automatically if set up correctly, but if in condenser, which I find hard to believe, then eventually it will pass into evaporator.
Pump out condenser, see if any oil in it like people suggest.
Better still, put R32 & air in it, then pump it down, but wear fire suit

[cricri]

What about the oil cooling?

[l2embo]

What about the oil cooling?

there is an air cooled 3 liter oil cooler. 71479e34-5720-45e9-8209-c5e1f339cbb2.jpg

[RANGER1]

12embo,
Can you advise on oil temperature & set point.
Usually 10 to 15 deg C above saturated condensing pressure.
So about 50 deg C.
Discharge temperature seems a little high, is oil filter clean, small pressure drop?
Can you increase suction superheat at all?
It might help reduce oil foaming.
If secondary oil separator working, would expect oil return to be quite warm most of the time.
Bitzer & Temprite have suitable oil separators with coalescer filter for optimal oil separation, maybe check against similar size machine, or capacity you have.
If velocity to high oil separator not likely to work.

https://www.bitzer.de/us/us/oil-sepa...he-oas-series/

https://temprite.com/downloads/920-920R_kW_Sizing.pdf

https://temprite.com/downloads/EmersonReport.pdf

[l2embo]

12embo,
Can you advise on oil temperature & set point.
Usually 10 to 15 deg C above saturated condensing pressure.
So about 50 deg C.
Discharge temperature seems a little high, is oil filter clean, small pressure drop?
Can you increase suction superheat at all?
It might help reduce oil foaming.
If secondary oil separator working, would expect oil return to be quite warm most of the time.
Bitzer & Temprite have suitable oil separators with coalescer filter for optimal oil separation, maybe check against similar size machine, or capacity you have.
If velocity to high oil separator not likely to work.

https://www.bitzer.de/us/us/oil-sepa...he-oas-series/

https://temprite.com/downloads/920-920R_kW_Sizing.pdf

https://temprite.com/downloads/EmersonReport.pdf

Hi again.
According to the technical data of the compressors oil cooler should start working when the temperature reach 110 degree centigrade and stop working when the temperature reaches 100. Although I agree with you according to my own experience which says the oil temperature should be about 55 to 65 degrees so I need to change the oil cooler maybe?
I did not find any oil separator with coalescer in Iran. Any suggestions?
By high velocity that you mentioned you mean the oil sepearator could be small?

[RANGER1]

Hi again.
According to the technical data of the compressors oil cooler should start working when the temperature reach 110 degree centigrade and stop working when the temperature reaches 100. Although I agree with you according to my own experience which says the oil temperature should be about 55 to 65 degrees so I need to change the oil cooler maybe?
I did not find any oil separator with coalescer in Iran. Any suggestions?
By high velocity that you mentioned you mean the oil sepearator could be small?

12embo,
When you say oil coolers starts working at 110 to 100 deg C, do you mean oil temperature???
Can you advise what your oil temperature is?
From your description you have air cooled oil cooler, so it would cycle fan on /off on a thermostat.
Maximum oil temperature, or control temperature I would think 45 to 55 deg C.
Mid oil temperature high, discharge temperatures will be high, oil carry over could be higher.
As far as oil separator I think a must to have coalescer type.
Ask Refcomp supplier to do the leg work.
They can import a compressor, why not oil separator.
I only know of Bitzer, Temprite, maybe Hanbell.

[l2embo]

I was talking about discharge temperature, although the maximum oil temperature according to the technical data is 120 degree centigrade 230 degree Fahrenheit. which I think is really high!

[Tycho]

I was talking about discharge temperature, although the maximum oil temperature according to the technical data is 120 degree centigrade 230 degree Fahrenheit. which I think is really high!

You need to change the setpoint for the oil cooler start... at those temperatures you may start "burning" the oil, that may be the reason why, as you say, the oil you are draining is very dirty.

Discharge temperature should be kept at 70-80C, and with an air cooler, oil temperature should be minimum 10C lower, preferably oil temperature should be like mentioned earlier, 55-65C


Looking at the picture below, the lower valve I have marked, is that a manual regulation valve for liquid to the Ice drum?

Also, next to the suction drum, that looks like a level control valve, is it working?
u5bc_20190725_154746.jpg

[Tycho]

l2embo,

I'd like to see a picture of the surge drum and the pipe arrangement around the surge drum.
Oil will form an oil rich layer on top of liquid R22, so I would like to see the oil drain arrangement as well

-The discharge temperature seems a bit high for that load on the compressor, what is the ambient temperature?

but there is a doubt that oil could possibly migrate into 3 meter vertical suction line and to the surge drum because of the pressure difference.

I agree with this

Looking forward to more pictures

[l2embo]

l2embo,

I'd like to see a picture of the surge drum and the pipe arrangement around the surge drum.
Oil will form an oil rich layer on top of liquid R22, so I would like to see the oil drain arrangement as well

-The discharge temperature seems a bit high for that load on the compressor, what is the ambient temperature?


I agree with this

Looking forward to more pictures

Dear Tycho

I attached some photos for your reference. Ambient temperature is about 33 but we are using water-cooled condenser with the working pressure of 150 psi.
About the oil drain arrangement I have to say we do not return the oil from the evaporator to the compressor since the evaporator is a second hand flake ice drum. Actually most of the oil stay in the condenser.

[RANGER1]

Dear Tycho

I attached some photos for your reference. Ambient temperature is about 33 but we are using water-cooled condenser with the working pressure of 150 psi.
About the oil drain arrangement I have to say we do not return the oil from the evaporator to the compressor since the evaporator is a second hand flake ice drum. Actually most of the oil stay in the condenser.

No no ice on float leg?

[Tycho]

No no ice on float leg?

I think we should all note that, as l2embo said. HP liquid is fed into the flooded system through the hand regulating valve that can bee seen in the middle of the attached picture, that feeds into the bottom of the drum.

Also in the same (last picture), connected into the middle of the "drop leg" pipe, is a pipe that is ice and frost free, connected to a level control valve, that is apparently not in use.

The last ice machine I worked on was a North Star, and it was identical in design as this one.

And the Liquid level in the surge drum was controlled by a danfoss RT thermostat (I forget what kind of RT, but it had a heating element), when the RT read a high delta T it would signal the level control valve to add liquid.

Liquid from the HP receiver was added in the drop leg, exactly as shown in these pictures exept it was using the level control valve and not a hand regulated valve.

and there was a functioning oil return by heat exchange from hp liquid.

so to stop beating about the bush and just lay it out:

So no offence to l2embo, but the oil temperature is too high, this again makes the discharge temperature too high, this again makes the oil less dense and more susceptible to follow the gas out of the compressor, the oil separator mounted on the discharge is too small (it would probably work on a small piston compressor, but it's much to small for the screw compressor). While I salute you for having managed to keep the correct level in the surge drum by using the hand regulating valve, you have to install an oil rectifier, and pipe the liquid feed through the level control valve if you want this system to work optimal and also have oil return to the compressor.
Oh and also to minimize oil loss, lower the discharge temperature to below 90C

[mbc]

Hi
you chose wrong type of oil
suniso oil were not compact able with screw compressor
in refcomp and bitzer screw compressor's
you have to use recommended oil
also you have a little bit oil and piping should be Wright to return oil
density of oils is less than R 22
So how you want to return oil from flooded evaprator from top of evaprator ?

[RANGER1]

Hi
you chose wrong type of oil
suniso oil were not compact able with screw compressor
in refcomp and bitzer screw compressor's
you have to use recommended oil
also you have a little bit oil and piping should be Wright to return oil
density of oils is less than R 22
So how you want to return oil from flooded evaprator from top of evaprator ?

mbc,
Refcomp manual indicates Suniso 4GS for R22 okay(6.2 technical data in manual attached from 12embo attached).
Other synthetic oils probably better, but evaporator sounds very contaminated.


https://www.hosbv.com/data/specifica...HandBook_E.pdf

12embo not returning oil at all because it is extremely dirty, assume secondhand evaporator.

[l2embo]

Hi
you chose wrong type of oil
suniso oil were not compact able with screw compressor
in refcomp and bitzer screw compressor's
you have to use recommended oil
also you have a little bit oil and piping should be Wright to return oil
density of oils is less than R 22
So how you want to return oil from flooded evaprator from top of evaprator ?

We also used B320SH oil which is compatible with the screw compressor and it makes no difference at all.
We do not return oil from our evaporator since it is a second hand flake ice evaporator. Moreover the oil stay in condenser.
Any other suggestions?

[mbc]

hi
again your oil separator is vary small you need oil separator about 40 liter volume

[l2embo]

hi
again your oil separator is vary small you need oil separator about 40 liter volume

I guess you are right. We are on the same point to be honest. But in this case I conclude the compact screw oil separation is just a joke. Could you please tell me if we need mesh oil separator or coalescer oil separator or some tank oil separator like O&F oil separators is ok? Did you claim the 40 liter on your experience or you select it from a catalog?
Regards

[mbc]

Hi Ranger

on page 3 it is indicate suniso 4GS is on request (I think they use different type of oil filter- high mesh /inch)

but on page 5 has more information

and this is another document from Refcomp.

[mbc]

Hi 12embo

second hand or new one there is no different in piping
it should be right
you have to have system it can return oil from evaporator
unless your oil will stay there and you loss oil and efficnsy

also oil circulate in our system
condenser is warm so oil can move very easy there
you have flooded evaporator and I wrote before density of oil and R 22 is different

[cricri]

Hi 12embo
you wrote: Hi RANGER1
1. Evaporator is a flooded flake ice drum

if your system is a flooded system, I can't see any device for an oil return from it.
So the oil missing in the oil separator is probably the oil drained from the ice machine + the oil mixed with refrigerant in the surge drum.

[l2embo]

Hi 12embo
you wrote: Hi RANGER1
1. Evaporator is a flooded flake ice drum

if your system is a flooded system, I can't see any device for an oil return from it.
So the oil missing in the oil separator is probably the oil drained from the ice machine + the oil mixed with refrigerant in the surge drum.

Sorry you are right. The system is not flooded. It is direct expansion with throttling valve.

[RANGER1]

12embo,
As Tycho mentions what controls level in vessel on flake ice machine.
Normally on clean system oil is returned to compressor with oil “skimmer” system.
Oil rich refrigerant taken from top of refrigerant level in surge drum returns through a heat exchanger to boil off refrigerant before returning to compressor.
From the looks of things Ice machine could have been on ammonia with the type of stop valves I see.

No refrigeration screw compressors run discharge temperature you are referring to, way to hot as we have all mentioned.
Oil would be so thin at those temperatures it probably be vapour or mist.
Please send more photos of how level is controlled in evaporator.

[RusBuka]

2019-07-29_12-33-10.png

Bad idea to use compact screw in that situation.

[RANGER1]

2019-07-29_12-33-10.png

Bad idea to use compact screw in that situation.

RusBuka,
Can you explain what is wrong with it?
Is it motor cooling or something, I can't quite see on your printout.

Thanks

[mbc]

hi 22 Embo

first you wrote it is flooded
then you wrote it is direct system with expansion with throttling valve
and then you put it control with level control
your photo shows your system is a flooded system

[cricri]

mbc,
it's a strange system.....
not flooded; the drum is only filed from the receiver. so there is no recirculation
no superheat control, the liquid injection should stop..... when the drum is full as the return line
no oil return

these ice machines are usualy empty of liquid, it flows along the drum wall
never that seen before

[l2embo]

mbc,
it's a strange system.....
not flooded; the drum is only filed from the receiver. so there is no recirculation
no superheat control, the liquid injection should stop..... when the drum is full as the return line
no oil return

these ice machines are usualy empty of liquid, it flows along the drum wall
never that seen before

Liquid overfeed system with gravity flooded evaporator.

[Tycho]

Liquid overfeed system with gravity flooded evaporator.

No, it's not "liquid over feed" because liquid overfeed would mean that liquid was pumped to the system from a low pressure drum. what you have is a DX (direct expansion system) where you have hand regulated the liquid feed valve so you can keep a steady level in the surge drum.

I have to give you kudos since you have been able to keep a steady level in the sure drum at 30% as I can see from the from the condensation on the surge drum.


Really, the way this system should be controlled is by using the level valve, that should ask for liquid from the condenser/receicer when needed, and it should go through a heat exchanger that exchanger would return any oil back in the compressor suction to ensure that the oil stays in the compressor circuit.

The way your system is piped, you may end up with a evaporator (ice coil) that will be clogged by oil and you will have less ice prodction.

[l2embo]

Dear Tycho
We did not drain any oil from the oil drain valve while we were changing the compressor. We are assuming that oil stayed in the condenser. Or is it possible that oil is in surge drum and the siphon under it ?

[NH3LVR]

What type of ice machine is this?
I have used this type of system with the North Star Ice Flaker and it works well.
I cannot see from the picture what kind of level control you have.

[mbc]

Hi Tycho
it is flooded system and refrigeration liquid control by the level control it has solenoid valve and hand REG valve .
liquid comes direct from reciver
on top they put surge drum ( same as liquid Separator )
also oil will stay in surge drum .

[Tycho]

Hi Tycho
it is flooded system and refrigeration liquid control by the level control it has solenoid valve and hand REG valve .
liquid comes direct from reciver
on top they put surge drum ( same as liquid Separator )
also oil will stay in surge drum .

mbc, I am well aware of what kind of system it is, I was simply pointing out that it is not a "liquid overfeed system". There is no overfeed going on in this system.

[NH3LVR]

It would be helpful if I had a reply to my question as to the maker of this ice machine.

[l2embo]

Sabroe Atlas 10 tons per day flake ice maker

[cricri]

NH3LVR,

from what I can see, it seems to be a Sabroe Atlas single drum. the size?? V156 => V619

[l2embo]

Dear friends
Thanks for your cooperation.
We have changed the compressor with a piston type copeland model 6RR2-400a-tsn the oil carry over problem still goes on.
The point is when we dried the ice maker drum before changing the compressor there was no oil in drum. What could be the problem? We are assuming the condenser is too big for system so the discharge gas easily pass oil separator because of the low condenser pressure. Is it possible? Condenser pressure is about 180 psi.

[RANGER1]

12embo,
180 psi or 1250kpa sounds good for shell & tube condenser to me.
Any oil foaming in compressor sight glass?
Oil return working?
Where is oil being drained from?
Is oil separator sized correctly?

[l2embo]

Dear friends
Thanks for your cooperation.
We have changed the compressor with a piston type copeland model 6RR2-400a-tsn the oil carry over problem still goes on.
The point is when we dried the ice maker drum before changing the compressor there was no oil in drum. What could be the problem? We are assuming the condenser is too big for system so the discharge gas easily pass oil separator because of the low condenser pressure. Is it possible?
Could the oil separator be defectivec

[Tycho]

Dear friends
Thanks for your cooperation.
We have changed the compressor with a piston type copeland model 6RR2-400a-tsn the oil carry over problem still goes on.
The point is when we dried the ice maker drum before changing the compressor there was no oil in drum. What could be the problem? We are assuming the condenser is too big for system so the discharge gas easily pass oil separator because of the low condenser pressure. Is it possible?
Could the oil separator be defectivec

Dear Tycho
We did not drain any oil from the oil drain valve while we were changing the compressor. We are assuming that oil stayed in the condenser. Or is it possible that oil is in surge drum and the siphon under it ?

Dear l2embo,

if there was no oil in the drum after you "dried" it, which I think you mean you pumped the system down and trapped all the liquid in the condenser, than that means that the oil is staying in the condenser.

Looking at your pictures, I now see that the big blue tank below the compressor is the condenser/receiver.

And that condenser/receiver is so large that there is probably not a lot of turbulence in it, so the oil leaving the compressor will collect, like I said before oil is lighter than R-22, in an oil rich layer on top of the R-22 liquid.

Also, since you are controlling the liquid level in the surge/suction drum with a hand regulating valve, and not using the liquid level control valve, I am kind of unsure how to advise you on oil return. because if the oil is collected on top of the liquid in the condenser/receiver, then it's kind of trapped there.

What is the liquid level % in the condenser?

[mbc]

hi

your piping and slope of pipe inside condenser is not right

what is the condenser brands you are using .

Also why you change the compressor ?

I think screw more better than piston type
for this type works .

[mbc]

Hi Tycho

if he pump down the system ,
oil should be on drum if there were oil
in pump down we sucking gas and oil were stay on drum

but to return oil ( oil is on top in flooded system in freion ) from drum he needs rectifier system .
I am family with those condenser's
design of pipes inside condenser is not right and oil especially POE oil were stay there .

[Tycho]

Hi Tycho

if he pump down the system ,
oil should be on drum if there were oil
in pump down we sucking gas and oil were stay on drum

but to return oil ( oil is on top in flooded system in freion ) from drum he needs rectifier system .
I am family with those condenser's
design of pipes inside condenser is not right and oil especially POE oil were stay there .

Yes, but look at the size of the condenser in the picture.
it is a very big condenser.
if oil and gas comes in from top and the gas condenses...

The liquid outlet is on other side of condenser.

you have very slow movement inside condenser, so oil will stay on top of liquid in condenser.

is what I am thinking.

If he has smaller condenser, with higher gas and liquid flow, then oil and liquid will go quickly from condenser to LP drum.

l2embo, says that when they pumped out the ice drum and LP receiver, there was no oil.

But he oil has left the compressor, so it has to go somewhere, yes?

That is why I am saying the oil may be staying in the condenser

Now... if l2embo keep running the system until the condenser is 70% oil, then the oil will start to go out to icedrum and expansiontank along with liquid from condenser, but he will also see that level in LP drum increases, even if he didn't add any *****.

Now I agree with you, he needs to add a rectifier system, but personally, I don't know any rectifier that works on a system with a steady stream of HP liquid. it needs to alternate.

If l2embo want's I can draw up a piping diagram for that ice machine, and an electrical diagram, but it would also mean that he would have to change the control system, to properly control the liquid level in the LP drum

So mbc, I am not here to arrest anyone or to make anyone look bad... I am doing my best to give input and help, from sometimes very little information. but I am here to help

[l2embo]

Tycho
we pumped down the LP side and trap all the gas in the condenser. we did not drain any oil from oil drain valve of the drum. we assume maybe the oil has been trapped inside the siphon under the surge drum. we also add nitrogen about 8 bar to drum for draining the oil but still get nothing.
about your question for liquid level I should say it is a small percentage HP liquid in condenser. if we open the throttling valve more than 1 turn we see high pressure liquid travels very very fast to LP side from the sight glass.
do you offer thermostatic expansion valve for that?
I would like to have your suggestion for piping and electrical diagram for the ice machine.
please also include what kind of valve is could we use for HP liquid control.

[l2embo]

Hi Tycho
please provide me with the diagrams if possible
regards

[l2embo]

Yes, but look at the size of the condenser in the picture.
it is a very big condenser.
if oil and gas comes in from top and the gas condenses...

The liquid outlet is on other side of condenser.

you have very slow movement inside condenser, so oil will stay on top of liquid in condenser.

is what I am thinking.

If he has smaller condenser, with higher gas and liquid flow, then oil and liquid will go quickly from condenser to LP drum.

l2embo, says that when they pumped out the ice drum and LP receiver, there was no oil.

But he oil has left the compressor, so it has to go somewhere, yes?

That is why I am saying the oil may be staying in the condenser

Now... if l2embo keep running the system until the condenser is 70% oil, then the oil will start to go out to icedrum and expansiontank along with liquid from condenser, but he will also see that level in LP drum increases, even if he didn't add any *****.

Now I agree with you, he needs to add a rectifier system, but personally, I don't know any rectifier that works on a system with a steady stream of HP liquid. it needs to alternate.

If l2embo want's I can draw up a piping diagram for that ice machine, and an electrical diagram, but it would also mean that he would have to change the control system, to properly control the liquid level in the LP drum

So mbc, I am not here to arrest anyone or to make anyone look bad... I am doing my best to give input and help, from sometimes very little information. but I am here to help

Hi Tycho
Please provide me with you recommendation on diagrams.
Regards

[Tycho]

Hi Tycho
Please provide me with you recommendation on diagrams.
Regards

Sorry for my late answer, but I have been out of town

But here is the way to control the oil return from your LP side.

I have been looking fro a proper drawing so I didn't have to make one myself..

draining-suction-line1.jpg

Now if you look at this picture.

On the left side is the oil return to the suction, there is a solenoid valve and a manual valve.
The solenoid valve should open 3-5 minutes after the compressor started. The manual valve should be a hand regulating valve, and after the hand regulating valve should be a sight glass, so you can correctly adjust the flow of oil/refrigerant going back into the suction.

If you look at the right side, there is a level control valve controlled by a simple regulator...

20 years ago when I worked on these machines, the level were controlled by a danfoss RT280, and they worked like a charm
https://assets.danfoss.com/documents...3586432642.pdf

[Tycho]

Sorry for my late answer, but I have been out of town

But here is the way to control the oil return from your LP side.

I have been looking fro a proper drawing so I didn't have to make one myself..

draining-suction-line1.jpg

Now if you look at this picture.

On the left side is the oil return to the suction, there is a solenoid valve and a manual valve.
The solenoid valve should open 3-5 minutes after the compressor started. The manual valve should be a hand regulating valve, and after the hand regulating valve should be a sight glass, so you can correctly adjust the flow of oil/refrigerant going back into the suction.

If you look at the right side, there is a level control valve controlled by a simple regulator...

20 years ago when I worked on these machines, the level were controlled by a danfoss RT280, and they worked like a charm
https://assets.danfoss.com/documents...3586432642.pdf

There should be pipe connections sticking out of your surge drum at all the appropriate levels