What do you mean by 'pelampung'? Is it the float?

if you refer to the 3rd photo in 1st page, the black ball on the left is the float. The white gadget is the intake valve that can shut the water flow.

Both are sold separately. Normally, only the intake valve is replaced... only one standard size. To be sure, you measure the pipe diameter, and buy the intake valve to fit the pipe.

Note that the white one in the photo is plastic... you can get a better one made of brass - about RM 25.

The black ball or float, it is attached by turning the ball onto the end of the rod.

Usually there's nothing wrong with the float, and the old one can be reused.

The brass valve is more 'heavy duty'. Worn out rubber rings/seals would caused slow leakage... but if the thin rod, which the float is attached to, broke...

If there's leakage and overflow, and you need to shut the main water supply because the intake valve is faulty, you can remove the valve and take it to the shop.

This way, you break the job into 2 sessions...

The pipe network could be simpler and fail-proof without using any check valves.

The water flow from the mains should branch at ground level, one going up to the tank, the other to the kitchen area at the back of the house.

The connection of the water from the mains to the outlet pipe from the tank is done so that the same tap can have water from either the mains or the tank? It doesn't make sense...