Liebert fan cooled condenser, they call for inverted traps at the condenser on hot gas and liquid lines. I have called Liebert to explain why this is done, seems the guy who knows was not in that day. I am starting up three Lieberts and the piping is not trapped at the condensers.I told the boss will not start them till piping is corrected. He wants me to explain this to him technically.
To put it in easy terms, to keep the liquid refrigerant from gravity flowing back down to the compressor during the off cycle. As the liquid flows back down the line it takes the oil back with it lengthening the time it will take to circulate back to the compressor. Also, if all that liquid flows back the discharge line and sits there on the discharge valves of the compressor you could have a problem with a valve failure somewhere down the line. If the condensers are located below the evaporator you don't have to trap the coil.
Don't let your ego get in the way of a good decision
tomt,,, I assume this is a liebert install outside and inside. If this system is being run year round as most computer room systems are that i've worked on , they are all trapped.You got to remember your discharge line runs all the way outside. In winter, oil will have a tendacy to pool at coolest location. Would'nt be a good warr. situation in case compressor(s)fail. Liebert won't warr. Hope this helps.
Regarding the inverted loop on the liquid line, there is no good reason for it. I've contacted a Liebert engineer about this in the past. Another tech who talked to Liebert told me the reason they want the liquid lines to have the inverted loops is because Liebert thinks we are just a bunch of dumb field guys, and if they only show an inverted loop on the discharge line we might mistakenly do the wrong lines, so they just show doing both liq & hot gas so they make sure we get the right one.
Regarding discharge lines, I agree they should be there for the reason of preventing gravity drainage of liquid refrigerant during the off cycle. I would take the stand you're taking, and not do a start-up until the hot gas lines are higher in elevation than the condenser, assuming the condenser is located higher than the compressor, which could allow siphoning of liquid out of the condenser, during the off cycle, onto the top of the compressor valves.
However, I have a friend who works at a company with dozens of Liebert condensers on the roofs, and none of them have inverted loops per the manufacturers drawings. These systems are several years old, and he rarely has a compressor failure. Not even one a year out of multiple dozens of compressors.
Bottom line, I think, is if there is any rise in the discharge line, such as at the roof penetration, that will prevent siphoning action, I think this will prevent the problem. Just compare it to the siphon action in a garden hose in a bucket of water on the roof.
Don't make the mistake, like some installers do, of installing the inverted loops like the Liebert drawing shows. This prevents legal electrical clearance into the controls section of the condenser. I usually put a piece of unistrut, horizontally on the side of the condenser, securing my discharge piping to that. I use long radius 90 degree ells and take the inverted loops between the top of the condenser coils and the top of the aluminum condenser housing.
Wherever it's practical to make the inverted loop is fine, even if it's right at the roof penetration.
Make it easy on yourself with your boss. Good standard piping practice has always been to invert the hot gas line to prevent liquid from sitting on the compressor discharge valves whenever the condenser section is higher than the compressor. He should have a Trane, Carrier or Copeland refrigeration piping manual. They all have showed this arranged for as long as I can remember. And that has been for 40 years and have all three, some being vintage 1946.
Good luck with a boss who should damn well know this if he is a contractor.