Capacity control Sabroe SMC112

[fabricioborges]

Hi, we have a Sabroe SMC112 compressor that has capacity control that works with pressure switches. but we do not have any information on the pressure settings of these pressostats. how can we know these pressures to see if capacity control is working properly?
during operation, we realize that even the suction pressure reaches low values (3.7 bar) the compressor does not decrease to 33%, remaining at 50%.

15016

[Grizzly]

Hi.
Welcome to the forum.
Could you tell me how old this compressor is?
Unless I am mistaken, what you are showing and describing are the loading gear solenoid valves.
Which nowadays are normally controlled via settings within the Unisab Controller on the front of the machine.
Does yours not have this?
The model you have in Brazil could well be without a unsab controller?
Can you advise further please!

Grizzly

[fabricioborges]

Hi, thanks for the reply. the plate of this compressor informs the year 2009 (see attachment). on the internet I researched and found these Unisab controllers, but our equipment does not have that. our compressor has 4 pressure switches on the side (see attachment) and by the electric diagram it controls the solenoids that change the capacity of the compressor. in the equipment documentation is very general and does not have the calibration data sheets of the instruments. so I am in doubt about the pressure values ​​of each of the pressure switches.

15017

15018

[RANGER1]

fabricioborges,
Pressure switches can be set to whatever you want, but not as good as a Unisab for easy set up & changing setpoint.
If you can tell us what temperature or pressure you want to control at & refrigerant, we may be able to help with settings with what you have.
At the moment if you run machine & carefully restrict suction stop valve on compressor & observe when compressor unloads to see current settings.
Sometimes an indicator light can be installed on each pressure switch to see if energized or de-energised.
Normally best way is to use nitrogen or air with accurate pressure gauge to set each switch individually.
Machine has to be isolated & depressurised.
They are Danfoss switches, so should be pretty easy.
Another older way to control them is with Danfoss RT1AL pressure switch with timers, so easy to adjust.

http://files.danfoss.com/technicalinfo/dila/01/DKRCC.PI.C00.E2.22.pdf
http://files.danfoss.com/technicalinfo/dila/04/IC.PI.P10.U3.53.pdf

[fabricioborges]

Hi, Thank you all for the attention and help. I'm not a refrigeration specialist. I am trained in mechanics and we maintain several equipment, among them, refrigeration compressors. in the case of this compressor, we realize that during operation, the suction pressure drops to reach 3.7 bar and even then it remains operated at 50% capacity. When this occurs, the tubing arriving at the suction begins to freeze. so we put the compressor in manual mode at 33% to avoid freezing in the suction. but in this case the compressor does not follow the variation of the external ambient temperature.
We use R404 refrigerant gas. the insufflation temperature varies between 10 - 15 ° C and the return temperature setting is 20 ° C. and we find that the low pressure switch acts with 3,5Bar pressure, turning off the compressor. we have in the panel, indication of which stage the compressor works (see annex)
I talked to the instrumentation technician who will help calibrate the pressure switches and he told me that by looking at the indication on the instrument face, the variation between the 4 pressure switches is small.
I would like to have an idea of ​​the correct values ​​to calibrate these instruments or some hint of how to calculate this.

15019

[Grizzly]

So who services you Sabroe equipment?
Whoever it is, presumably deals with Sabroe.
If you contact Sabroe (Marine) Brazil.
I would expect them to be able to help you.
As they have software apps which can determine the settings you need.
In the Uk and Europe their tech support is really good and they are Helpful.

I would assume the guys in Brazil would be the same.
Try raising the set point on the pressure switch with the lowest setpoint.

Logically it should raise the lp control setpoint.
However if as you say you are unsure then you need to enlist the help of a local refrigeration Engineer.
3.7 bar = -7.9c / relative by the way.
Has this problem recently occurred?
If so, you need someone to come and check out what is happening.

Because the comp does not change its duty whereas the pressures in the lp side of the system can be influenced by many things!

Its possible you have a malfunctioning pressure switch or someone has been playing with the switch settings.
Without really knowing what they are doing.
Get a Tech in to have a look, or at least speak to someone more local than us remote forum guys!
Good Luck Grizzly