A machine having an efficiency greater than 50 percent, is known as reversible machine.
A machine having an efficiency less than 50 percent, is known as irreversible machine.
A machine having an efficiency equal to 100 percent, is known as ideal machine.
Non-reversible Machine If a machine is not capable of doing some work in the reversed direction, after the effort is removed, then the machine is known as non-reversible or self locking machine. The condition for a machine to be non-reversible or self locking is that its efficiency should be less than 50%.
A screw jack used for lifting the load is a non-reversible machine or self locking machine.
Reversible machine If a machine is capable of doing some work in the reversed direction, after the effort is removed, then the machine is known as reversible machine. The condition for a machine to be reversible is that its efficiency should be more than 50 %.
Non- reversible or self locking machine If a machine is not capable of doing some work in the reversed direction, after the effort is removed, then the machine is known as non-reversible or self locking machine. The condition for a machine to be non-reversible or self locking is that its efficiency should be less than 50 %.
Velocity ratio of a machine is the ratio of load lifted to the effort applied.