People in the industry mix and match to get their desired results in a certain situation. The results can vary. It would be better if i compare similar operations with examples of actual projects
Let us take the case of installation of Condensers in a Thermal Power Plant.
- Winch/Chain Pulley and Roller- This technique has been adopted by Indian Mechanical contractors due to its low cost. It's not skidding but still we can say its close to it. However, there is a big risk involved in such operation. For example...What if there is an error in the inclination of the roll? The roll is uncontrollable at certain point. It's always a heart stopping affair. Then again in countries like India where projects are won by lowest price bidders, risks are neglected most of the times.
- Strand Jacks and Rollers- Recently introduced. Cost is slightly above the "winch and roller system". Instead of winches, Strand jacks are used to pull the frame on which the condenser is mounted. The problem again is the controllability of the procedure. Manual stoppers are used to stop the roll. Also, when the frame is pulled which is mounted on the rollers. The rollers tend to displace from their intended place and then has to be corrected manually.
The total time to skid in is 3days.
Photographs: Left top- Rollers adjusted after dislocation. Left middle- View from the pulling end. Left bottom- Single strand jacks pulling the condenser. Right- View from side showing the U rail.
- Push Pull Cylinders on Skidding Tracks- Probably the safest method because of the controllability of the skidding process. The push pull cylinders can either push or pull the package. The Package is placed in the skid shoes and inturn the skid shoe is over a teflon matted skid track. Liquid soap etc. is used to reduce friction over the teflon mats.
