Maintenance jobs is very effect on performance during overhauling of air compressor

Explain the following maintenance jobs is very effect on performance during overhauling of air compressor

(a)     Big end bearing & main bearing

(b)     Suction valve & delivery valve

(c)     Piston & cylinder

(d)     Intercooler

1/2001, 4/2002

(a)           It is should be checked properly when compressor overhauling. Worn down bearing can cause the compression noisy, vibration, overheating and excessive bumping clearance.

                The effect of excessive bumping clearance gives a large clearance volume which will be full of air at high pressure when the piston reaches the end of its stroke, and in double-acting compressors it also reduces the clearance at the lower part of stroke.

                On the out-ward stroke of the piston the air within the clearance volume expands until the pressure within the cylinder is low enough to allow the suction valves to open. With a large clearance volume the outward travel of the piston will be greater before the pressure is low enough within the cylinder to allow the suction valves to open.

                In consequence a large part of the suction stroke is made ineffective and the amount of air taken into the cylinder during each suction stroke is reduced. This lowers the volumetric efficiency.

(b)           It always should be good working order condition, according to running hour. The air compressor valve are dismantled, cleaned, and refacing thoroughly check spring plate, etc., and reassemble and test leakage.

                It a suction valve does not reseat promptly at the end of the suction stroke due to a weak spring or to carbon deposit, part of the air drawn into the cylinder will be returned through the defective suction valve during the first part of the delivery stroke.

                It a delivery valve is slow in reseating, for the same reasons, part of the delivered compressed air will return to the cylinder during the first part of the suction stroke.

                So this is reduced the compressor performance.

(c)           It should be checked when overhauling the compressor. Remove piston, clean piston ring groove, piston ring, take the gap clearance of piston ring a sealing rings and scraper ring should be good working order condition.

                If the piston rings are leakage, the compressed air leak into crankcase and reduces the compressor efficiency and contaminates the L.O.

                If the scraper ring is not in good working condition, the lubricating oil can deposit to valves and it causes the valves to carbonized and sluggish action. L.O is mixing with compressed air disturb the air starting system. It can cause to air line explosion and also increase L.O consumptions, deposits at intercooler and reduce cooler efficiency so piston and cylinder should be good working condition.

(d)           The function of intercooler is to reduce the air temperature and volume reduce at constant pressure as low as possible and volume reduced at constant pressure and also to drain oil and water vapour. This lowers the work done in compressing the air and prevents a lot of the mechanical problems which could arise if the air temperature were uncontrolled.

                By keeping the air temperatures low, less difficulty is experienced with the lubrication of the pistons and cylinders and the suction and delivery valves remain in a cleaner condition without becoming fouled with carbonized oil.

                So that intercooler should be cleaned air side and water side for to get perfect cooling efficiency.

Air compressor maintenance (4) each

(a) big end and main bearing (b) suction and delivery valve (c) piston and liner (d) inter-cooler

1/2001, 4/2002

(a) Bearing

                Air compressor main bearing and top end bearing and crank pin bearing clearance must be check regularly for safe operation.

            Excess clearance of bearings may increase clearance volume, mainly reduced volumetric efficiency, and fall of compressor performance. Excess clearance of bearing may cause over loading, striking, and insufficient L.O pressure tends to bearing failure.

            So the finest clearance must be adjusted on top end, bottom end and main bearing.

            During over haul check the crank pin and holding down surface Check the bearing surface if it is wear or crack should be replaced. Check the bearing nut for tightness and locking arrangement and proper lubrication of bearing.

(b) Suction and delivery valve

                Air compressor valve needed regular overhaul if they are defective reducing the volumetric efficiency and also reduce air delivery, increase air temperature and increase running time.

                Valves can leak due to wear and fatigue, insufficient or over lubrication, present of foreign particles, oil decomposition and excessive lift.

                At regular interval valve seat, valve plate needed to be properly ground due to their constant pounding effect. Check the valve seat, valve plate; buffer plate, damper plate for pitting, over heating and carbon deposit.

            Check the spring weak or defective one to be renewed. Absolute cleanliness of filter and minimum absolute lubrication can longer life of suction and delivery valve.

(c) Piston and liner

            Air compressor Piston rings and cylinder liner to be regular over haul. The defective piston ring and wear cylinder liner can not get effective seal it can reduce the volumetric efficiency, reduce air delivery and increase running time.

            Piston rings and cylinder liner can wear due to lack of lubrication or L.O contain condensation of water can cause poor lubrication and dirt contain suction air.

                At regular interval piston ring to be renewed and check the cylinder liner for wear and take calibration if necessary renewed.

(d) Inter cooler

                The effect of operating with fouled inter coolers will be to raise the air temperature. This will cause lubrication difficulties, the compressor efficiency will rapidly fall off and there may be the rise of an explosion caused by overheated parts in the air system.

            Air side can be reduce cooler efficiency due to deposition of oil, on the cooling surface due to over lubrication and suction air contain dirt. It can be thoroughly cleaned by chemical.

                Waterside can be reducing cooler efficiency due to clog of particle and dirt inside cooling water. It can be thoroughly cleaned. And then cooler to be tested by hydraulic pressure to twice the working pressure.