whenever the water is filling up in the water-tank especially toward the max level the pipe starts to hammer.water hammering arrestors are not available in my country or too expensive.is there any way to solve this problem?
It is probably hammering because the float is creating waves which are causing the float of open and shut the valve. An air chamber ahead of the float valve should dampen the hammer if it does not eliminate it entirely. Otherwise you have to create a chamber for the float that does not transfer the wave oscillations from the main tank to the float.