What can be the issues if a control valve response time getting slower day by day?

The response time of a Control valve getting slower day by day due to the aging effect. we can remove this effect.

Due to ageing effect & friction due to dust, moisture lead to delay response. So, clean trim of valve and put some lubricant. 

Note: oil & lubrication not  to be used in oxygen gas and burning gas.

these are the  reasons  which found in hydraulic sys working slowly

pump performance 

condition of suction stainer  and out pressure filter 

adjustment of pressure control valve