How It Works

Working Principle of Hydraulic Jack

Basically jack climb up on the jack rod (Part of the lifting trestle) with the required pressure to lift up the load. Its action is similar to monkey that climbs a trunk tree; i.e, first it holds up on to the trunk with its legs and lunges upwards, then it holds on to the trunk with its hands and lifts its legs up. At any time, either its hands or legs have a grip on the trunk that prevents it from falling down.

Similarly, the air hydraulic jack, air hydraulic bottle jack and jack is provided with two pairs of jaws, a lower pair of jaws and an upper pair of jaws for a perfect grip. During lifting, both the pairs are "locked". In this position the jack is only allowed to move upwards. During lifting, the lower pair of jaws grip the trestle rod while the jack lifts up. After completing the full stroke, the upper pair of jaws grip the trestle rod while the base of the jack moves upward. During the process of lowering, any one of the pairs is always locked.

• First Foundation Is Completed,Base/Bottom Plates And Top Most Shell Plates Are Erected And Welded,Roof Structural,Roof Plates & Top Angle Ring Welded For Truss Supported Roof Of The Tank.
• Tank Jacking Equipments Placed/Errected At Adequate Distance.
• Hydraulic Connections Are Made To All The Jacks And To The Powerpack With The Help Of Hoses And Fittings.
• Clean Hydraulic Oil Is Filled In The Oil Tank Through The Oil Filler Breather Provided At The Oil Tank Till The Level Mentioned At The Oil Level Gauge.
• Electric Motor Is Started-And Care To Be Take For The Direction Of Electric Motor-Should Be As Per The Arrpw Mentioned On The Cover Of The Electric Motor.
• On Energizing The Hydraulic Powerpack,The Shell Plates Along With The Roof Is Lifted By The Hydraulic Jacks To The Required Height.
• Next Shell Course Is Erected And Welded.
• Jacks Are Lowered And Shell Is Connected To The New Shell Plates And Operation Is Repeated For The Balance Shell Plates.
• After The Last Shell Plates Are Welded In Position,The Jacking Units Are Dismantled.

Shell To Bottom Plates Welding Is Completed.

Description of Principle of The Erection System

The following description gives a brief outline of working procedure of air hydraulic jack and air hydraulic bottle jack. However, modifications can be certainly made if required. (Refer the drawing below to develop better understanding).

• The tank bottom-plates are placed on the prepared foundation and welded together
• Spacers cum guide beams of maximum 400 mm height are tack welded to the tank bottom along the periphery. The plates of the first shell ring (in fact the top ring of the tank) are positioned and welded together
• The beams or lattice work of the roof are assembled and finally joined to the upper rim of the shell ring. Inner sheets of the roof are placed and welded together
• The lifting equipment is assembled by following a standard method. The plates of the second shell ring (next to top ring) are positioned outside the first one
• The completed part of the tank (the roof and top shell ring) is lifted hydraulically to a height, at which the plates of the second shell ring can be moved into place and the roof sheeting can be completed, except for about 2 or 3 roof plates which shall not be fixed until completion of the tank for air to pass through
• The plates of the second shell ring are located exactly and welded together to the lower edge of the first shell ring
• The plates of the third shell ring are placed outside the second shell ring
• The completed part of the tank (the roof and the two uppermost shell rings) is lifted
• The above cycle of operations is repeated until the last (bottom) shell ring is finished
• The entire tank is lowered down to the bottom plates and welded to this. The lifting equipment is dismantled

Determining The Number of Jacks To Be Used For Any Tank

Number of trestles required for the tank depends on various factors such as :

• The maximum weight of the tank. The vertical load is max 8, 12 or 25 ton per trestle, depending upon the type of jacking equipment selected
• The maximum wind load on the trestles.
• The maximum distance between the lifting points in the shell with regard to the stability of shell.
• The normal maximum distance between the trestles is 3 mtrs.