R290 rerigerant

[kay86]

Hello, I have a question about A3 refrigerants, R290 and R600A. I know that precautions must be taken when working with these two flamable and explosive gases, however I've also read that the low pressure on the suction side can cause air to get inside the circui if there's a leak, and this could cause an explosion if the correct ration between air and gas is achieved. Is that true? If so, how do we make sure this doesnt happen?
Thank you!

[Brian_UK]

The mixture of released flammable refrigerant from the refrigeration system and air in atmosphere must be within a certain mixture range. No explosion can occur if R290 presents with less than 39 grams per cubic meter air or above 177 grams per cubic meter air.


The first action to take is to ensure that the installation is to industry/legal standards, strength and pressure testing shold ensure that you have a leak free system. A satisfactory vacuum test is also required.

The installation of a low pressure cut-out switch set to a positive pressure should prevent the system running at a negative pressure.

[frank]

Sounds like a college question

[kay86]

The installation of a low pressure cut-out switch set to a positive pressure should prevent the system running at a negative pressure.

Hi Brian, thank you for your answer. Regarding the cut-out switch, I believe these are used in larger sytems, right? Because at home I have two A3 class refrigeration systems and I'm unable to locate this component. One is a R290 blast chiller with a LBP compressor, and another one is a freezer with R600A gas. I'm trying to make a DIY solution very similar to the R290 chiller that I already have, so LBP compressor, condenser, dryer, capillary tube and evaporator. I am not a professional but I'm reading a lot (and yet I recognize I still have much to learn) in order to do everything at high safety standards. Altought I believe the charge will be quite small, like 50-70 grams, I don't want to take any risks of endangering myself or my property. I am familiar with the procedures required to ensure that the circuit is leak free, that is nitrogen pressure test, vacuum check and so on... However, I would like to understand more about this negative pressure thing. With a LBP compressor you can achieve very low temperatures on the evaporator and very low pressure at the suction inlet. I'm not sure if they can be lower than atmosferic pressure, but they might be. Lets say the brazing is damaged over time, for example someone hits is or there is corrosion (not something that could happen in my case, but still...) what would happen? Air could get sucked in and contaminate the refrigeration gas, right? But I assume the compressor would stop working long before an explosive concentration of gas is formed inside, because it would have to suck roughly 20 times more air than there is propane and a circuit in that condition would never work. Am I correct?
Thank you

[kay86]

Sounds like a college question

Hi Frank, I'm not sure what you mean. If you think that I'm doing some kind of school project or homeworks, that's not the case. I'm just a hobbist trying to make a cold trap for a project of mine. I've tryed asking to some professionals in my area, to provide me with their service for a price but they never replyed. I guess that designing a refrigeration system is something too time consuming for the amount they're confortable charging me with. Anyways, I reiterate, I'm very well informed of the dangers working with A3 refrigerants so I want to understand what tools and what knowledge I need to have in order to work with all the safeties in place.