I have seen a number of damaged by spinning backwards due to bad check valves. There is still a lot of differences between the true industrial screws and the commerical screws. Some of the lighter duty industrial machines are moving closer to the commerical machines. More machines are being built with rolling element bearings and pressure differential lube oil systems and no oil pump.

Under some operating conditions, there is insufficient oil differential to feed the oil with enough oil. A rolling element bearing can run in an oil mist and still perform, but it still has to have oil.

When a screw compressor looses the thrust bearings or balance piston, the rotors will move toward the compressor suction and can contact the suction housing.

As far as I'm concerned, the true industrial machines still have hydodynamic film sleeve bearings for the main journals and some are offered with tilting pad thrust bearings. Thes machines require a positive pressure lube oil system driven by an external pump. With the pressure lube oil system, they can operate over a much larger range of operating conditions and not cause compressor damage.

The industrial compressors have both a suction and discharge check valve. Some of the commerical machines have only one check valve ar the compressor.

I really can not tell much from the posted photos. What were the compressor operating conditions and has the compressor experienced excursisons outside of the normal operating parameters?

Ken