I did post a reply to the other thread you started on this topic.
About 10 years ago now I did one of my first Flash Presentations which just happened to be on the Enviroguard system. For about a year I was commissioning them at the rate of about 1 a week.
Have a look at this link...
Enviroguard Presentation
The presentation even has setting instructions for the SPR Valve.
Remember, very importantly, these systems do not have subcool. They should never have subcool. the "quick diagram" states subcooled liquid but this is in reality not true.
Since these system float the head they require more refrigerant than a standard system - hense the side vessel.
Here is a copy and paste of my reply to the other thread you started...
The idea here is to float the head pressure and so drop the annual energy costs by up to 40% compared to a fixed head pressure system
This system is usually coupled with electric defrost because sometimes the head pressure can get so low the liquid line freezes - this means low heat-flux from the hot (or Kool) gas.
There is no subcooling designed into the system. Unless you use a liquid pump (Hysave LPA) you have to locate these systems a good few meters above all the evaporators and you most certainly cannot run your liquid lines up or even any significant horizontal distance before going down. Liquid lines generally must go down about 5m before going horizontal.
During summer and high load conditions there is greater flash gas in the evaps and so less liquid there and the warmer liquid in the liquid line expands and the liquid volumes collecting in the condenser tubes reduces and so the side vessel is used to store the excess liquid not needed for summer. During winter the velocity through the condenser slows and so liquid collects there, the cooler liquid in the liquid line is more dense (less voluminous) and there is less flash gas in the evaporator causing liquid levels there to increase which all leads to the need for greater system refrigerant charge in winter which comes from the side vessel.
There is a tube running from the SPR valve to a larger tube, normally with a sight glass, that is charged with the same refrigerant as the system, that sits outside the unit in the air-on but out of the sunshine. The SPR valve compares head pressure to ambient temperature via this tube system and if head pressure rises say 14K above ambient then it is assumed that there is too much liquid in the condenser, raising head pressure unecessarily causing greater power consumption, also starting to cause unwanted subcooling, and so the SPR valve opens to drain liquid from the condenser and into the side vessel.
A small continuous draining from the side vessel to the system suction via a discharge desuperheating heatexchanger takes place to ensure the system has more liquid available anytime as conditions change during the day and seasons.
One of the other advantages of this system is that it tells you very early on if you have a refrigerant leak. Case temperatures rise very soon after a small amount of refrigerant is lost.