Single purchase Crab Winch

Single purchase Crab Winch

In a single purchase crab which, a rope is fixed to the drum and is wound a few turns round it. The free and of the rope carries the load W. A toothed wheel A is rigidly mounted on the load drum. Another toothed wheel B, called pinion, is geared with the toothed wheel A as shown in Figure.

Let                  T1       =          No. of teeth on the main gear (or spur wheel) A,

T2       =          No. of  teeth on the pinion B,

I           =          Length of the handle

r           =          Radius of the load drum

W        =          Load lifted, and

P          =          Effort applied to lift the load at the end of the                                                                handle.

In one revolution of the handle, distance moved by the effort

=          2π l

Number of revolutions made by the pinion B

1

and number of revolutions made by the wheel A

= T₂ / T₁

Number of revolutions made by the load drum

= T₂ / T₁

And distance moved by the load

Now                M.A.   = W / P

and efficiency,

η= M.A. / V.R.