Check valve is a back pressure valve deployed in the BHA to prevent high pressure from getting into the work string and then to the surface.
The valve consists of a valve body, two subs, hold-downs, balls, springs and O-rings. It is low-maintenance due to fewer components.
The valve is run on coiled tubing. If flow reverses, the valve closes and holds pressure from below the valve. The valve re-opens when back pressure from above the valve exceeds one from below.