For flange leakage, you need to tight the bolt again. If not yet, open the flange to see if there is any damage to the flange gasket. For packing leakage, you need to compress the packing gland. If the packing is too loose, then add more packing. If the leakage is directly on the body, weld it (only in low pressure). If it is in high pressure, please give it up directly for safety.
It is not easy to check out the internal leakage problems. Firstly, you may not close it completely, so close it forcibly again. Secondly, the sealing ability of valve seat is damaged, you need to regrind it. For valve
core damage, you have to check whether it is damaged by scour or medium erosion, but the sealing surface need to be welded no matter in what situation.
Generally, sealing surface damage of valve seat/valve core will cause the internal leakage, so you can grind the valve seat/ valve core sealing surface to repair it. But in special situation, if the valve is electric or pneumatic, it is possible that the valve stroke isn’t set well.
For external leakage, you have to see where is the leaking point, if it is the valve body itself, you can only change it.
Internal leakage can be ascribed to sealing surface problem, so repair the sealing surface to see if it is leaky again. For external leakage, different valves can have different leaking points, so it should be treated differently. For filler leakage, you can tight the packing or change a new one.
have a lot of leaking points. In most cases, gland is the leaking point. So, open the gland, supplement or replace the packing and tighten the gland. For internal leakage, it is caused by broken sealing surface which is on the top of the valve core, but practical experience tells us that sometimes internal leakage is likely caused by the hard objects got stuck on the valve core. So the specific method is to open and close the valve back and forth several times so as to wash away the hard objects. If it is the valve problem itself, then you should to replace the valve
at your convenience.