Friday, November 14, 2008

maintanance and inspection of screw compressor

The installation should be inspected regularly at intervals that will be determined by the severity of operating conditions. For convenience, suggested maintenance routine may be segregated into two separate but interdependent classifications as follows:

I] OPERATION INSPECTIONS
An accurate operational inspection system is the best means of detecting the need for maintenance work.

a) Continuous log or graph of all pressure and temperature readings should be kept. For the first few weeks of operational break-in, 4 readings per 8 hour shift are recommended. After that, the readings could be reduced to a suggested minimum of two per shift. Any rapid changes in consecutive readings would indicate possible malfunction and should be investigated immediately. Any gradual but consistent change not related to normal ambient or process variations should also be investigated.
b) Any change in the characteristic should or increase in vibration of the unit should be investigated.
c) Oil and water leaks should be repaired when first observed.
d) The water flow from jacket, after cooler and oil cooler should be observed when each reading is taken.
e) Check lube oil level in reservoir.
f) Make all checks recommended for the main driver.

II] PERIODIC INSPECTION
a) Every 500 – 700 hours: Check operation of alarms and controls.
b) Every 1000 – 1500 hours: Drain oil sample from reservoir. Check oil for oxidation, contamination and water. Frequency of oil change depends upon this analysis.
c) Every 7500 – 8500 hours (Annual):
  • Inspect rotors through inlet and discharge nozzles. Some polish areas on the rotor lobes are to be expected, due to float and relative shift of the rotors during start up and shutdown. Excessive rubbing between rotors or wear on radial and end sealing strips will require readjustment or possible replacement of the bearings.
  • Remove discharge end cover and inspect timing gears. There should be even wear pattern on gear teeth.
  • Measure thrust bearing end clearance with a dial indicator. Measure dial bearing clearance with a dial indicator mounted through thrust bearing housing drain opening.
  • Loosen inlet end cover and visually inspect radial bearings.
  • Remove compressor jacket cover plates and inspect for sediment or calcium deposits. Clean if necessary.
  • Remove coupling guards and inspect couplings for broken shims.
  • Recheck alignment at all couplings.
  • Check and reset, if necessary, all temperature and pressure gauges and pickups.
  • Inspect inside of silencers for deterioration of foreign materials.
  • Inspect water side of after cooler and oil cooler for foreign material or calcium deposits and clean if necessary.

d) Every 15000 hours (2 years):

  • Inspect per paragraph 2c.
  • Remove coupling hub at inlet end cover. Measure inlet radial bearing clearances with a dial indicator mounted adjacent to the bearing.

e) Every 30000 hours (4 years):

  • Inspect per paragraph 2d.
  • Remove and inspect timing gears, thrust bearings, radial bearings and seals.
  • With radial bearings in place, indicate shaft runout at all diameters of each shaft with a dial indicator.
  • If condition dictate, remove the rotors from the housing, clean and inspect the rotors and housing bores.


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