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38 Cards in this Set

  • Front
  • Back

What is another name for single acting compressor?

Truncated or trunk style

In a single acting compressor what does the piston attach to?

Directly to the connecting rod

What are throws?

They are the attachment points of the connecting rods located on the crankshaft

what are some advantages of having a cast iron piston?

-they expand at the same rate as the cylinder

-can withstand high temperatures

-they don't wear very much

when is a cast iron piston generally used?

on large slow moving compressors

when are aluminum pistons generally used?

-they are commonly used on high speed reciprocating compressors to help with vibration caused by the inertia of the reciprocating parts.

-they may also be used to balance out the two stages so that weights are similar

what lubrication method do smaller trunk style compressors use?

the splash method, it both lubricates and cools off the compressor

what is another name for a piston pin?

wrist pin

what are the 2 types of piston pins?

1)full floating


explain what a full floating piston pin is

full floating pison pins are free to move inside both the con-rod bushing and the piston bushing. they are held with snap rings on either sides of the piston bore

explain what a semi-floating piston pin is

semi-floating piston pins can either be locked onto the connecting rod and free to move on the piston bushing or be locked to the piston and free to move in the con-rod bushing

a double-acting compressors piston is connected to

a piston rod that is then connected to the crosshead which connects to the con-rod

rider bands support the weight of....

the piston and half the weight of the piston rod

what are a few different ways that a piston can be held onto the shaft?

-against a shoulder with a nut

-tapered shaft and nut

-multiple bolts holding the piston parts onto a flanged piston rod

what is rod runout?

it is when the piston rod isn't running totally straight through the packing

what is rod loading?

rod loading can be either in compression or in tension

- compression occurs as the piston moves towards the head of the cyl, the force of the discharge pressure on the piston tends to buckle or bend the rod

-tension occurs when the piston is heading towards the crosshead and is under extreme pull pressures

what problems can be caused by excessive rod loading?

-damaged crosshead adn con-rod bushings

-frame failures

-valve problems

-broken or bent piston rods

what is net compression?

the difference between suction and discharge pressures

what parts are most commonly affected by excessive rod loading?

-the crosshead pin and bushing

-the con-rod bushing

what is rod reversal?

it refers to the reversal of the rod load from compression to tension. its a good thing. when the rod is in compression all the clearance on the crosshead pin is to one side allowing it to be lubricated, when it goes into tension the clearance is shifted to the opposite side of the bushing and can have its turn being lubricated

what is a tail rod?

a tail rod is a common method of compensating for lack of rod reversal by equalizing the surface area. it reduces the capacity of the compressor but is often necessary to ensure rod reversal

if you need to grind out scratches on a rod, what is the rule of thumb for how much material you can remove?

usually no more than 0.002" per inch of rod diameter if the original size packing rings are to be used again

how you check is a shaft is straight?

put it in v-blocks or between centers of a lathe. set up a dial in the center and spin the rod

do oil rings exist on double acting compressors?

no, only on trunk style compressors

what are some benefits of using synthetic piston rings over cast iron?

-they outlast cast iron rings

-better with abrasion, corrosion, and acidic gas

-soft enough they dont score the cyl

-almost no break in period

(cast iron rings are very cheap though)

why is there an end gap on a compression ring?

it allows for thermal expansion

how does the compression ring seal?

through a combination of cyl pressure, ring tension, and oil film

what are the different types of piston ring joints?

-butt joint

-angle joint

-step joint

how do you check ring end gap?

by placing the rings together in the cyl at the smallest ID. this may be at BDC for single acting or in the middle of the stroke for doubling acting compressors. (the high pressures tend to make a very slight buldge in the tube)

what are the different types of rider bands?


-angle cut with a side relief groove

-angle cut with pressure relieved face and side grooves

-double twin ring rider ring

in what situation do you need to use uncut rider rings?

when they pass over a valve port

in what situation do you nee to use the double twin ring rider ring?

they are made for use on pistons that are to short to have separate grooves for the piston rings

how are uncut rider rings installed?

manufacturers can provide a rider ring pre-stretched and mounted on a carrier ring that fits over the piston

how do you set the piston to cylinder head clearance?

by turning the piston rod into or out of the crosshead and then locking it into place

what is the general rule of thumb for setting the piston clearances?

if the manufactureres specifications arent available you must set the crank end clearance at 1/3 and the head end clearance at 2/3 of the total. this accounts for thermal expansion

what is a balance nut used for?

they are used to fine tune the weight balancing of opposing multi-stage reciprocating compressor parts

piston speed is constant while traveling from BDC to TDC. true or false?

false. its depends on the angle of crank throw

Card #38