Here is the original Image for clearity (this machine is bit small but significant pressure)


[1]. its the Connection to the pipe.
[2]. A joint that connects the pipe of upper tank [4]. and to the pipe for normal use [1].
[3]. its the connection to the down tank from where the water is transferrred to the UPPER tank
[4]. The tap u can is to close or open the transfer of water to upper tank you can close it to increase the pressure to the connection of pipe at [1]. all u have to do is to call the plumber and get the joint [2] and [1]
and that's all