EVACUATING SO2 - DEJA VU!

EVACUATING SO2 - DEJA VU!


We know from reading the GE service manual that GE sold small canisters of R-12 for the purpose of adding it to their sulphur dioxide monitor tops. The R-12 would combine with the mineral oil and thin it out enuf to enable the oil to leave the evaporator and return to the compressor.


In my career as a refrigeration mechanic I did considerable work on low temperature cascade refrigeration systems both very large and very small. On the smallest systems on the low temp compressor in a recharge procedure we would add R-12 from a 30 inch vacuum to bring it to 0# PSIG. We would then static pressure charge the system with the R-503 to the required static pressure shown on the label. The R-12 requirement was not on the label but we were told by the manufacturer that it was what did when they were manufactured.


Here is a link to a RSES article on small cascade refrigeration systems and the additives added for oil return.
www.rses.org/assets/serviceapplicationmanual/620-58a.pdf     
The refrigerants in the article are obsolete and no longer used.


The larger and largest cascade refrigeration chambers used at the time R-13. On the label the static pressure charge was given and the ounces of pentane needed for oil return. We would add the needed ounces of pentane at a 100 micron vacuum and then static charge the machine to the name plate requirement with R-13.

When we evacuated a system we used large heavy cast iron Sargent Welch scientific vacuum pumps that were mounted on wheels so they could be moved. The oil capacity for these pumps was probably a half gallon or more in the sump. When used to evacuate the systems with pentane added the pentane removed would combine with the vacuum pump oil and the oil level would rise in the vacuum pump. The oil would thin out enuf so that we sometimes had to change the oil to obtain our 100 micron requirement. We would always change the oil after each evacuation.


I recently released the charge on my 1938 GE flatop and removed the float assembly and added a capillary tube and charged it with Envirosafe HC refrigerant. I will create a post on that in the future.


I had purchased an air venturi vacuum pump to see if it would evacuate the system and was disapointed that it would only draw about 20 inches with my air compressor that matched the stated cfm requirements. From that 20 inch vacuum I switched to my small portable Robinair with a small oil reservoir.

When I returned to check on the vacuum reading the pump was noisey and the oil level was over the top of the sight glass and I had about an 8 inch vacuum. Deja vu Pentane in the oil.


The vacuum pump did not work after one two and three oil changes as the thinned out oil was stuck in the vanes of the pump. After multiple oil changes and running the pump after each change to get the new oil into the vanes the pump eventually worked. I was able to eventually finish evacuating the system.


An unforgettable event. I can remember reading at least one other person having a disastrous time evacuating an SO2 system. It is my judgement that GENERAL ELECTRIC used pentane as an oil additive in the 1938 model year. The refrigerator is running excellent on the HC refrigerant and since the HC refrigerant is entirely miscible with mineral oil there is no reason or need for pentane.