2026-07-22 · AmmoniaEquip Engineering
Oil-injected twin-rotor screw compressors earn their keep on large ammonia plants because they run long hours with stepless capacity control. They fail expensively when shaft seals weep, slide valves stick, or rotor-to-housing clearance grows beyond the oil film.
The first diagnostic is oil. Dark, metallic, or ammonia-diluted oil usually precedes a seal leak or bearing smear. Check suction filter differential, oil-separator level, and slide-valve position feedback before opening the casing. Many “failed rotors” are actually a starved oil pump or a blocked injection line.
When the housing is opened, inspect male and female rotor lobes for scoring, foreign-object dents, and thrust-face wear. Measure bearing play and compare to the last overhaul. Replace mechanical shaft seals as a complete set with the mating ring; polishing a grooved carbon face and sending the machine back is a short-term patch.
Capacity and Vi slides need free travel. Carbonised oil on the piston or a seized solenoid valve will hunt at part load and overheat the discharge. After rebuild, laser-align the coupling to the motor. Screw packages are less forgiving of angular misalignment than older piston sets.
AmmoniaEquip overhauls Grasso and other major-brand screw packages in the workshop: rotors, bearings, shaft seals, gasket sets, and alignment. If the plant cannot wait for a full strip, we stage a seal-and-bearing intervention with a documented clearance report so the next shutdown is scheduled, not forced.