A rotocap is a parts of exhaust valve which is used to rotate the valve by 8 to 10 degree when exhaust valve open. But do you know How Rotocap Works ? It’ theory , working and functions.
What is a Rotocap ?
A Rotocap is an instrument which is used as a valve rotator to rotate the exhaust valve of auxiliary engine forcely while opening.
Before knowing about its working, first know about its function.
Function of Rotocap
- Even heat transfer through out the seat of the valve. :-
- To reduce the abrasive wear of seat of valve
- To decrease soot deposits on the surface of valve stem and seat.
- To avoid from burning of the exhaust valve.
- Proper seating of valve on valve seat.
1.Even heat transfer through out the valve seat :- The valve rotated by rotocap during opening of the valve to ensure the even transfer of heat to the seat of valve. Even transfer of heat through out the valve helps in avoiding the pitting, local hot spot occur and heat distortion on the valve seat.
2. To reduce abrasive wear :- Abrasive wear occur due to rubbing or friction due to hard particles ( formed due to improper combustion and catalytic fins present in fuel ). Due to rotation abrasive particles not stick on valve.
3. Reduce soot deposits :- Due to rotation soot will not stick on surface.
4. Protect from burning of exhaust valve :- Rotocap help valve from burning. If there is no rotocap available causing hard particles stick on seat. Due to sticking of hard particles, valve will seat properly and cause exhaust gas leak from it. Due to leaking wire drawing effect takes place and valve get overheat. Thus, burning of exhaust valve. So, due to rotation, it get prevented.
Summary of function of Rotocap
Rotocap fitted on exhaust valve rotate the valve and ensuring the proper heat transfer, reducing wear down of valve seat and protecting from burning.
Parts of Rotocap
The main parts of Rotocap are following :-
- Retainer body
- Ball race
- Spring washer
- Spring collar
- Retainer rings
Constructions of Rotocap
The retainer body shown in the figure has 4 or 5 grooves or pockets. These pockets are arranged circumferentially. For each pocket there are balls. These balls are kept on race known as ball race.
Coil springs are also kept in each grooves with ball in ball racer. The ball race provide a path for ball. The spring washer which seat against inner rin of the retainer body through the retainer collar.
A Rotocap which is a self-contained assembly of balls and ramps. It consists of a valve plate with six slots machined into it for balls to roll through.
In each ball slot, there are a spring and ball. When ball pressed run to spring and and back in opposite directions after removal of force of stem.
Working of Rotocap or How rotocap works ?
As we know the exhaust valve open when the rocker arm pushes the valve stem (when cam pushes push rod ). So, during the opening of exhaust valve , due to load it makes the belvel spring flat. Now the belvel spring apply the force on each ball kept on ball racer and track. Due to force of belvel spring, ball try to move in the track and pushes the spring kept in the path of ball ( ball racer ) i.e ball force transfer to the spring washer or coil spring. The spring force now transfer the force to the valve inner rim or ramp.
Thus, each inner ramp get force of equal amount so it get rotated by 6 to 8 degree.
Now when the valve getting close, then belville washer starts to come in their shape ( conical ) and leave the force on ball so ball come on their original position.
brief description of its working
We the Exhaust valve start opening when push rod pushes valve stem then It start pressing the belville spring and it get flat. when the washer get flat it start pressing or transferring energy to the ball and ball start moving against spring in the ball racer an transfer ball energy to the spring and finally to the ramp. Ramp is fixed to te valve.
Maintenance on Rotocap
If you get high temperature of exhaust valve then it may be due to burning of valve. So, we need to overhaul the valve and check Rotocap.
Or, During maintenance of cylinder head or decarb of auxiliary engine we need to dismantle all the parts and need to check for any damage or crack, carbon deposits, spring damage.
If the valve shows signs of a defect or irregularity, replace it with a spare if one is available. If there are no spare parts available or there are few signs of defects, then disassemble the Rotocap for maintenance. Make sure to replace all of the springs, clean all of the tracks, and inspect the ball condition. It is necessary to ensure that the balls are perfectly round and that the spring washers are in good condition.
Note :- Never try to fit back damage parts or spring retainer plate. It is much cheaper to replace it in place of fitting same damage parts. This is all about maintenance of Rotocap fitted in exhaust valve.
How do you know your exhaust valve burning ?
If the temperature of all unit are ok and one unit temperature keep on increasing then we know it is burning of exhaust. There are so many reasons for burning of valve. One of them is that Rotocap not working properly i.e valve is not rotating.
How will you test your valve is rotating properly or not ?
At time of the overhauling of cylinder head , mark the valve and body . With the help of mallet hit on stem of valve. Now check that marking is same or not. If marking is not
Note:- Due to Rotocap, valve rotate 6 to 8 degre in one direction. Keep in mind that it only rotate in one direction.
Also keep in mind that rotocap only works during of valve not during closing.
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