I hope my concern isn´t real.
Did i understand correct. Those wheels you can remove the rack ? What kind of springs you have. You should test with some weight before you instal. Be aware that those wheels doesn´t carry so much weight. I use same kind of wheels in my work and they carry about 8 kg per pair and they look little bit heavier. I know You do best choice. I´m just little worried.
Anyway the rack seems to be fine.
Let me see if I can explain.
There is no weight on the wheels. There are there to keep the rack centered in the space above the tank. They will role in a track that will be mouted to the walls vertically. They will also keep the rack from swinging forward and back or hitting the walls when being raised or lowered as well as to keep the rack from banging around in an earthquake. The spings will keep the wheels extened and in contact with the tracks while providing a bit of "forgiveness" like shock absorbers compared to having the wheels fixed in place with a nut. This will help insure that the rack doesn't bind up between the walls when being raised or lowered.
In this picture of my original light rack, if you look closely at the corners of the light rack, you can see wheels. You can also see a line on the wall from the wheels rolling up or down when the rack goes up or down. The spring loaded wheels will be a similar concept except that they will run in a track and never contact the wall directly.
The empty rack weighs less than 20 pounds which almost 1/3 of my existing rack which was made from 2"x2" wood as well as some plywood. When I get done installing the LED fixtures and my neptune moon lights, I figure it will weigh around 50 pounds fully loaded. The rack is suspended from 4 stainless steel cables (one at each corner) which run through pullies to my electric winch in the closet next to the tank. The new rack will be hung the same way. See pictures above and below.
In the picture below, you can see the winch. The current winch is capable of 2000 pounds but is very noisy and way overkill. It will be replaced in the near future with an electric slide actuator with a 400 pound capacity. The slide actuator will be much more quiet, slower and more precise as I will be able to limit its travel with limit switches. It will automatically stop before the light rack reaches the ceiling where as the current winch stops when I release the button. If I am not paying attention, I could go to far and rip the rack apart. That hasn't happened thank God!
As far as the rack coming apart. I made it so the center pieces can be removed in order to get the rack in through the door opening above the tank. Essentially, I ground down the center fittings that join the aluminum channels together. They are still tight but loose enough that they can be pulled apart or put together above the tank. Without grinding them a bit, it would have been nearly impossible assemble or dissasemble in the confines of the space above the tank as it takes some real force with a mallet to get the fittings that hold the rack together inside the aluminum channel.
Here is how the new aluminum rack comes apart. The larger sections are small enough to fit through my 36"x36" doors above the tank.