Questions and answers about Bell Hydromatics
Q 1: What is the largest size
of a tank that can be erected using jacks?
A: Our jacking equipment has been used for the
following largest size of tanks according to data available : a) Largest
in diameter : 92 meters. b) Largest in height : 64 meters. c) Largest
in weight : 1900 tons These, however, are not limiting figures.
Q 2: 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 fragments of the same height as that of the shell
Q 3: What is the type 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.
Q 4: What is the ambient
temperature range in which jacks can be used?
A: The jacking equipment can be used in the
temperature range of 10 degrees Celsius to + 50 degrees Celsius.
Q 5: 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.
Q 6: Can the powerpack be
placed outside the tank?
A: The powerpack can be placed inside or outside the
tank. If the powerpack is placed outside the tank. The main hydraulic hose
line is brought inside the tank through the gap provided by spacer beams or
through the manhole.
Q 7: How do personnel enter
inside the tank when the jacking system is used?
A: Spacer beams of about 300 to 400 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.
Q 8: What is maximum safe
wind speed at which a tank can be lifted using jacks?
A: While the safe wind speed large depends on
parameters such as diameter, weight, height of tank, number of jacks in use,
the number of jacks is determined so as to make lifting safe at 23.5 m/s
(strong gale wind), in general.
Q 9: Can the jacks be placed
outside the tank?
A: For repairs to tank bottom plate or foundation,
the 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.
Q 10: Can we use a
combination of 12 ton and 25 ton jacks in the same tank?
A: 12 and 25 ton jacks should not be used
simultaneously in one tank. For any one tank, jacks of the same rated
capacity shall be used.
Q 11: What is the life
period 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 not subject to corrosive environment, the expected life of the
equipment can be safely considered as 10 years.
Q 12: 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
minimum shell plate width (height) of 1400 mm and maximum of 2500 mm. For
shell plates having width (height) of 3000 mm or more, jacking equipment can
be supplied against specific requirements.
Q 13: During the
construction of a tank using jacks, is it possible for air to get
accumulated inside the tank and lift the tank off the ground?
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.
Q 14: What if a hose bursts
or oil seal ruptures during lifting?
A: he jack is a fail-safe device. Even in the event
of hydraulic seal, the mechanical grip jaws prevent the jack from moving
downwards and will hold the jack at the same position on the trestle rod. In
case of a hose rupture during lifting, lifting should be stopped and the
hose replaced. The jacks do not slip downwards with the load even if the
Q 15: 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. At any given point of time, either one of
the pairs is engaged or locked. 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.
Q 16: Will all jacks lift
evenly or will there be some difference in the lifting time of all the jacks
in one tank?
A: There is some differential lifting depending on
the path used by the oil in the hydraulic line to reach the jacks. Some
jacks may lift before others, however this is not a cause for concern due to
the oil cushion effect.
Q 17: 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 welded 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 welding. In case heavy winds are expected
during this period, the tank should be tied with guy ropes.
Q 18: Will tank come down if
the powerpack fails during lifting?
A: In case during lifting, the powerpack fails due to
any reason, the pressure in the hydraulic line is maintained and the jacks
remain stationary in the semi-lifted position.
Q 19: If the lifting is
uneven, can the jacks be used to correct the tilt, if any?
A: In the event of uneven lifting, which at any time
can be to the maximum extent of the stroke length of the jack, which is 100
mm, individual jacks can be shut off using a stop cock valve to make any
adjustments during lifting.
Q 20: Should the roof plates
be fixed before the erection of jacking equipment?
A: All roof plates except one or two plates (or more
if the diameter is more than 24 mtrs) can be fixed before the erection of
jacking equipment, provided the height of the top shell is more than the
length of the trestle. In case the height of the top shell is lesser than
the length of the trestle, then the top two courses shall be erected before
fixing the trestles, or alternatively, the annular roof plates can be fixed
after the top shell is jacked up.
Q 21: What is the minimum
thickness of shell plates suitable for jack-up method?
A: The minimum thickness of shell plate than can be
used for jacking method is 6 mm. However, additional precaution as advised
in our instruction manual shall be taken while jacking up of 6 mm thick
plates to avoid buckling of 6 mm plates. For plate of 8 mm and more
thickness, additional patch plate or curved angle are not required.
Q 22: What is the time taken
for lifting a tank up by 2.5 mtrs.?
A: The time taken for one lift of 100 mm is approx. 5
minutes. Therefore for 2500 mm, 25 such lifts are required, which would take
approx. 125 minutes. However, as practically observed, the lifting duration
required to lift 2500 mm for large diameter tanks ranges from 4 to 6 hours.
Q 23: What is the stroke per
A: The stroke length of the jack is 100 mm.
Q 24: What if the oil is
getting heated up?
A: There is no cause for concern till the oil
temperature is less than 70 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
Q 25: What is the shipment
time required for jacks?
A: Shipment time would vary from 6 weeks to 10 weeks
(plus transit time) depending upon quantity and capacity of jacking
Q 26: Whether automatic
girth welding machine can be used when the tank is being constructed using
jacking system ?
A: Automatic girth welding is commonly used with the
jacking method. The outside welding is completed and inside tack welding is
done before lifting. Inside full welding is done after lifting such that the
welding level is above the height of the trestles.
Q 27: How to determine the
number of jacks to be used for a particular tank?
A: The number of trestle required for a tank is
settled by: a) 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 b) The maximum wind load on the trestles. c) The maximum distance
between the lifting points in the shell with regard to the stability of
shell. d) The normal maximum distance between the trestles is 3 mtrs.