Piston Rings

Here Are The Piston Rings Questions And Answers Which Will Help You To Understand So Many Things

Question: What Is A Piston Ring And Why It Is Used?
Answer: A Piston Ring Is A Cast Iron Compression Ring, Fitted In The Piston Groove Such That These Rings Provide A Packing/seal Between The Piston And Liner. The Purposes Of Fitting Piston Rings Are:
1. They Do Not Allow The Hot Combustion Gases To Escape Towards The Scavenge Space.
2. They Transmit The Heat Taken By The Piston During The Entire Cycle Mainly Combustion Period To The Liner Walls.
3. They Help To Maintain The Cylinder Lub Oil Film Between Piston And Liner, Thus Carrying Out Boundary Lubrication With Point To Point Metal Contact. Cylinder L.O. Is Being Injected In The Upward Motion Of The Piston, Between 1st And 2nd Piston Ring And A L.O. Film Is Created Due To The Smearing Of Oil Due To Movement Of Piston Rings With Piston.

Q. How Many Piston Rings Are Used And What Are Their Types?
Ans: Generally 3-4 Piston Rings Are Used In One Piston. The First Ring Is A Controlled Pressure Relief Ring, It Is Thicker With Respect To Other Rings And Has A S- Type Of Groove, The Purpose Of CPR Is To Take The Most Of The Heat Induced On The Piston Crown, Thus Reducing The Amount Of Heat To Which The 1st Compression Ring Is Subjected. Thereby, Increase In The Life Of Compression Rings. Then There Are 2-3 Compression Rings Below It, The Basic Difference Is In Their Cuts, These Are Opposite As We Proceed Down. If The First Ring Is Right Hand Cut Second Will Be Left Hand Cut, It Is To Minimize The Escape Of Combustion Gases Through Them.

Q. What Do You Mean By Piston Ring Butt Clearance, How Is It Measured Onboard And Its Importance?
Ans: Piston Ring Butt Clearance Is The Cut That Is Made In The Ring Such That Due To Thermal Expansion The Ring Doesn't Collapse. Secondly, This Cut Makes It Possible To Fix And Remove Them. The Method Of Measuring Butt Clearance Onboard Is Paper-impression Method. When Liner Is Taken Out For Overhaul , A Piston Ring Is Inserted From Bottom Of The Liner And A Paper Is Placed On The Butt, An Impression Appears On The Paper Due To Oily Surface. This Paper Is Then Taken Out And The Clearance Is Measured By The Help Of A Vernier Caliper. It Should Be Around 0.5% Of The Liner Bore Diameter. If It Exceeds That Piston Ring Is Changed. However, It A General Practice To Change Piston Rings During Every Liner Or Piston Overhaul. 
Importance Of Butt Clearance: 
1. If All The Butts Get Aligned, The Combustion Gases Blow-by Or Blow Past Takes Place Which Might Lead To Scavenge Fire. 
2. If The Butt Clearances Of Any Piston Ring Decrease, The Ring Might Collapse And Not Seal The Gases.

Q. What Are An Oil Control Ring Or Oil Scraper Ring And Its Purpose? 
Ans: An Oil Control Ring Is A Type Of Piston Ring Used In Trunk Type Engine Which Nowadays Are Used As Auxiliary Engines. These Oil Control Rings Are Fitted In The Piston Skirt, In A Ring Groove Which Has Holes Through The Piston. The L.O. From The Sump Which Travels Up Through Gudgeon Pin For Piston Cooling, Goes Into The Groove While The Piston Is In Upward Travel And Is Smeared Into The Liner Surface. While Travelling Downward, The Oil Control Ring Scraps Down The L.O. From Liner Surface And It Is Sent Back To L.O. Sump. This Is Why It Is Also Known As Oil Scraper Ring.

Q. What Are The Main Reasons For Piston Ring Breabreakage?
Ans: 
1.    Piston Ring Breaks Due To Collapse Of The Ring Which Can Be Due To High Wear Of Rings High Liner Wear, Loss Of Lubrication Film. 
2.    Over Lubrication Can Also Lead To The Ring Breakage, By Hindering The Rings To Move Freely And Causing Fatigue Cracks. 
3.    Too Low Lubrication Feed Rate Can Cause Deposits Build Up Due To Absence Of Detergency Effect Of Cylinder Oil. It Can Lead To Loss Of Lubrication Film Resulting In Blow By And Collapse Of The Ring. Improper Running In After Renewal Of Piston Ring. 
4.    Uneven Wear Pattern Of The Liner Can Cause Excessive Stresses On The Rings Which May Led To Breakage. 
5.    Excessive Ovality, Clover Leafing And Formation Of Wear Ridges On The Running Surfaces Can Also Cause Piston Ring Breakage. 
6.    Worn Or Damage Piston Grooves And Improper Piston Ring Clearance. 
7.    Excessive Combustion Pressure Can Cause Over Stress To The Piston Rings. 
8.    Faulty Injector Or Improper Fuel Temperature Can Cause Incomplete Combustion And Excessive Deposits Which May Lead To Collapse Of Piston Ring. 
9.    Over Expansion Of Rings During Fitting. Use Standard Tools For The Fitting Of Piston Rings As Per The Manufacturer Recommendation. 
10.    Improper Piston Ring Design Or Inadequate Material. Use Rings As Recommended By Maker.