The efficiency of a screw jack is maximum, when Where α = Helix angle and ϕ = Angle of friction.

Explanation

Concept : The maximum efficiency of screw jack is when helix angle α is Note: If the friction angle is greater than the helix angle, the torque required to lower the load will positive, indicating that an effort is applied to lower the load. Such a screw is known as a self-locking screw. Additional Information Screw jack A screw jack is a portable device consisting of a screw mechanism used to raise or lower the load. There are two types of jack Hydraulic and mechanical A Hydraulic jack consists of a cylinder and piston mechanism. The movement of piston rod is used to raise or lower the load. Mechanical jack can be either hand operated or power driven The maximum efficiency of screw jack is: