Valves vary widely in form and application.Sizes typically range from 0.1 mm to 60 cm.
Special valves can have a diameter exceeding 5 meters. Valve costs range from simple inexpensive disposable valves to specialized valves which cost thousands of US dollars per inch of the diameter of the valve. Disposable valves may be found in common household items including mini-pump dispensers and aerosol cans. A common use of the term valve refers to the poppet valves found in the vast majority of modern internal combustion engines such as those in most fossil fuel powered vehicles which are used to control the intake of the fuel-air mixture and allow exhaust gas venting.Źródło: https://en.wikipedia.org/wiki/Valve
Ideally, it was the service, which have used our friends or that is recommended on internet forums.Only such a professional company will be good, if we want our hydraulic system worked flawlessly.
It is important, however, that even the smallest failure to call the appropriate professionals, because even if something on the surface it seems to us trivial, inadequately repaired, can result in a much higher failure and pretty large problems.
It is so much simpler, cheaper and better solution than self-repair..