• Q1 : What is the type and quantity of hydraulic oil required?

    A : General purpose hydraulic oil from MOBIL or other reputed manufacturer can be used. Although hydraulic oil of 68 viscosity is largely used for most conditions, the viscosity of oil shall be recommended based on ambient temperature at site.

    As a general thumb rule the minimum required quantity of oil shall be derived as follows:

    For 12 ton single acting jack : 3 litres per jack. ] Subject to minimum of 300 litres.
    For 12 ton double acting jack : 4 litres per jack.
    For 18 ton double acting jack : 4.5 litres per jack. ] Subject to minimum of 400 litres.
    For 25 ton double acting jack : 5 litres per jack.

  • Q2 : Can the jacks be placed side the tank?

    A : For repairs to tank bottom plate or foundation, jacks are placed outside the tank. In this case, appropriate temporary support arrangement is to be made to support the trestles and stay pipes, such that the load is distributed to the ground evenly.

  • Q3 : Can the jacks be placed outside the tank?

    A : For repairs to tank bottom plate or foundation, jacks are placed outside the tank. In this case, appropriate temporary support arrangement is to be made to support the trestles and stay pipes, such that the load is distributed to the ground evenly.

  • Q4 : What is the maximum width or height of shell plates that can be erected with the jacking system.

    A : The standard jacking equipment can be used for maximum shell plate width (height) of 2500 mm. For shell plates having width (height) of 3000 mm or more, jacking equipment can be supplied against specific requirements.

  • Q5 : During the construction of a tank using jacks, is it possible for build up of air inside the tank?

    A : It is advisable to have one or two openings in the roof by not fixing one or two roof plates till the shell is fully erected, for air to pass through. All vents in roof shall be open till jacking is complete.

  • Q6 : What if a hose bursts or oil seal ruptures during lifting?

    A : The jack is a fail-safe device. In the event of a hose rupture during lifting, the mechanical grip jaws prevent the jack from moving downwards and will hold the jack at the same position on the trestle rod. Lifting should be stopped and the hose replaced. The jacks do not move downwards with the load even if the hose bursts.

  • Q7 : Is it possible for the tank to fall down during lifting or when held by the jacks?

    A : Each jack has two pairs of case hardened grip jaws made of special grade of steel. During lifting both the pairs are in “locked” position. In this position, the jack can move only upwards. Therefore, the tank cannot fall down when held by the jacks. During lowering of tank, one of the pairs of jaws is locked, which is loaded & hence prevents the tank from gravitational fall.

  • Q8 : Should the roof plates be fixed before the erection of jacking equipment?

    A : When the top-most shell course (first course) is erected, openings shall be left in roof at jack locations to allow the trestle column to protrude through the roof. These openings shall be closed with roof plates after the top shell course is lifted up.

    All roof plates except two to four plates (or more if the diameter is more than 30 mtrs) can be fixed before the erection of jacking equipment, provided the height of the top two shell courses is more than the height of the trestle.

  • Q9 : What is the minimum thickness of shell plates suitable for jack-up method?

    A : Precautions such as fixing a temporary stiffener ring and pad plates for lifting lugs shall be taken while jacking up of 6.35 mm thick plates or plates of less than 6.35 mm thickness to avoid buckling of plates.

  • Q10 : What is the time taken for lifting a tank up by 2.5 mtrs.? 

    A : The time for lifting a tank upto 2.5 mtr height is as follows:

    Using double action jacks – 40 minutes

    Using single action jacks – 3 to 4 hours

    Double action jacks work 5 times faster than single action jacks.

  • Q11 : What is the stroke per lift? 

    A : The stroke length of the jack is 100 mm or 10 cm.

  • Q12 : How do personnel enter inside the tank when the jacking system is used?  

    A : Spacer beams of about 450 mm to 500 mm height are provided around the periphery of the tank on the tank bottom plate. The shell plates are placed on these spacer beams. Personnel can enter into and out of the tank through the gap provided by these spacer beams.

  • Q13 : What is maximum safe wind speed at which a tank can be lifted using jacks.   

    A : The safe wind speed large depends on parameters such as diameter, weight and height of tank and the number of jacks in use The number of jacks is determined so as to make lifting safe at maximum 22.5 metres per second (81 km/hr) (strong gale wind), in general.

  • Q14 : Will all jacks lift evenly or will there be some difference in the lifting time of all the jacks in one tank?   

    A : All jacks are connected to a common powerpack. When the powerpack is operated, oil flows to all jacks and an oil cushion is formed. The load is balanced on the oil cushion. The powerpack pumps oil at a constant pressure to all jacks simultaneously.

    In theory, the flow with which oil is pumped from the powerpack is equally divided into the number of jacks being used. However, there could be some differential lifting between all jacks used in any given tank, since oil finds the path of least resistance. Assuming that there is a difference in level at two opposite points in a tank, of 100 mm (which is the maximum stroke of the jacks), and the diameter of tank is 90 m, then the inclination is 0.06 degrees.

    If the tank diameter is 20 mtrs, then the inclination is 0.28 degrees.

    This can be absorbed by the in built elasticity in the tank shell. After all jacks complete their stroke of 100 mm, the tank is perfectly horizontal.

  • Q15 : How long can the tank be left in lifted position, i.e., when the load is on the jacks?   

    A : Normally, after the lifting is done, immediately the next shell plate is put in placed and fitted up to the previous shell plate, thereby releasing the load from the jacks. It is not advisable to keep the jacks loaded for more than the time required to place the next shell course in position and fitting up. In case wind of velocity more than 22.5 m/s is expected during this period, the tank should be tied down with guy ropes.

  • Q16 : How to determine the number of jacks to be used for a particular tank. 

    A: The number of jacks required for a tank is determined by:

    The maximum weight of the tank. The vertical load is max 12, 18 or 25 ton per jack, depending upon the type of jacking equipment selected

    The wind load on the trestles (shall not be more than 22.5 metres/second).

    The maximum distance between adjacent jacks, which shall not exceed 3.5 mtrs.

  • Q17 : What is the ambient temperature range at which jacks can be used?  

    A : The jacking equipment can be used in the temperature range of – 10 degrees Celsius to + 50 degrees Celsius.

  • Q18 : Can we use a combination of 12 ton & 18 ton jacks in the same tank? Can we use double acting & single acting jacks together in the same tank? 

    A : 12 and 18 ton jacks should not be used simultaneously in one tank. For any one tank, jacks of the same rated capacity and type shall be used.

  • Q19 : What is the life of the jacks? 

    A : The jacks are of robust design and construction. If periodic maintenance is carried out as per our recommendation and the equipment is protected against corrosion, the expected life of the equipment can safely be considered as 10 years.

  • Q20 : What is the shipment time required for jacks?  

    A : Jacking equipment can be shipped from India within two to six weeks (plus transit time) depending upon quantity and model of jacking equipment.

  • Q21 : How much time and how many men are required to set up the jacks.   

    A : 15 to 20 man-days are required to install upto 50 jacks in one tank. Lifting of tank upto 2500 mm takes 40 minutes and requires 2-3 men from amongst the site crew.

  • Q22 : Whether tanks with column supported roof be erected using jacks?  

    A : Tanks with column supported roof can be safely erected using jacking equipment, by fixing 1 or 2 jacks on each column. The column will be erected in segments of the same height as that of the shell plates.

  • Q23 : Can floating roof tanks be erected using jacks? 

    A : Floating roof tanks can be erected using jacking equipment by fabricating the deck in the clear space available inside the tank and placing the pontoons after erection of shell and removal of jacking equipment. (The jacking equipment occupies approx. 2000 mm of annular space inside the tank periphery).

  • Q24 : If the tank has tilted due to foundation settlement, can jacks be used to correct the tilt?  

    A : Individual jacks can be shut off using a stop cock valve to make any adjustments during lifting. Any tilt in a tank can be corrected by lifting the tank using only one half of the jacks.

  • Q25 : Whether automatic girth welding machine can be used when the tank is being constructed using jacking system? 

    A : For tanks built “TOP-DOWN”, single side SAW automatic girth welding machine is used for horizontal welds. First outside horizontal welding is completed using the BYGGING Single Sided SAW Girth Welding Machine. After outside welding is completed, the load is released from the jacks, lifting lug and fend off lugs are cut-off, and the jack trestles are retracted away using our Trestle-Tilt TM mechanism to provide space for the AGW. Thereafter internal welding is done using the single sided SAW girth welding machine. After welding, trestles are moved back to their original vertical position, ready for the next lift.

  • Q26 : What if the Oil gets heated up? 

    A : There is no cause for concern till the oil temperature is less than 80 degrees celcius. In case it exceeds this figure, lifting should be stopped and the oil allowed to cool down before resuming lifting. If there is abnormally fast heating of the oil, please contact our technical support. Powerpack shall be kept under shade to prevent excessive heating of oil.