pressure control valve

i have separator and at this separator blowdown valve and at the downstream there is pcv (fail open) found and after that filter is found when we want to depressurized the filter the flow goes in the reverse direction what is the effect of this reverse direction at control valve and its componant(seat,plug nad cage)

If I understand you correctly you have a filter downstream of the PCV in a separator blowdown line. When you backwash the filter you want to know that happens at the PCV. Is this correct? You haven't given us any brand/model information on the PCV, but based on my general experience with them most PCVs are not going to function in a reverse flow condition. You might need to place a bypass valve in a loop parallel to the PCV. When the filter is backwashed open the bypass valve. A check valve may be suitable as well, you'll have to decide if that is appropriate.

i have reverse flowed these valves in the past for short periods of time, you just loose some control over it if you were trying to do pressure control. You can always look into a V ball which i use a lot of (fisher) and are rated for bi-directional flow.