How do you know if there is an air lock in sand filter?

An air lock in a sand filter can be detected by observing reduced water flow or pressure in the system. You may also hear gurgling or bubbling noises as air is trapped within the filter. Additionally, if the filter's pressure gauge indicates a significant drop, it can be a sign of an air lock. To resolve this, you can typically bleed the air by opening a valve or manually releasing trapped air.