How could it went wrong in such a valve? 1

[phage]

The valve in the photo has little mechanical parts. It cannot went wrong.

However, in the next photo it leaks.

Could anyone provide a reason and how can I repair it (instead of replacing one)?

 

[TugboatEng]

Tighten the packing nut. If that doesn't fix it you need to replace the packing.

 

[LittleInch]

Few moving parts, but one of them is the shaft that comes out of the body that has a seal.

For cheap valves like this it is probably an O ring but might be packing. This seal isn't working.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[gerhardl]

As said from others: thighten sealing.

Apart from that, there is a long list of what might have caused the leaking:
Abrasion from dirt or dried media on stem and sealings
Too hot/cold media or temperature variations
Pipe/pipe parts or valve/parts moved by unproper support and fastening
Corrosion
Unsuitable media
Uncorrect handling/closing/opening force giving mechanical damage
Mechanical parts and sealings outside manufacturing tolerance
..... and so on

Simple things are not always simple..

 

[monkeydog]

Looks like water not very hot not very cold.
Why would there me abrasive material in the liquid?

 

[gerhardl]

When you do not know anything of a failure then you list up all possible causes, then you start to check and eliminate.

A broken pipe upstream repaired or unclean water source could put anything into the pipe from silt, dirt, gravel, metal filings up to twist. It does not have to be anything of this.

'Damaged sealing' cover most of this but explain nothing.