Answer EKG Question 24

Q24. With regards to main transmission shaft flange coupling arrangements:
A. Sketch a hollow type coupling bolt and the hydraulic head/nut and loading rod which are used to fit it;
B. Describe how the bolt is fitted;

C. State the advantage of the hollow coupling bolt as compared to the traditional type of coupling bolt.

Answer: A. Sketch of hollow type coupling bolt and the hydraulic head/nut and loading rod which are used to fit it; 

B. Fitting method; 

The Pilgrim hydraulic bolt uses the principle embodied in Poisson’s ratio to provide a calculated and definite fitting force between bolt and hole.

The bolt is hollow and before being fitted is stretched with hydraulic pressure applied to an inserted rod from a pressure cylinder screwed to the bolt head. Stretching makes the bolt diameter small enough for insertion into the hole, after which the nut is nipped up.

Release of hydraulic pressure allows the bolt to shorten so that

(1) Predetermined bolt load is produced and

(2) diametrical re-expansion gives a good fit of the shank in the hole.

C. The advantage of the hollow coupling bolt as compared to the traditional type of coupling bolt.

These bolts prevent any misalignment between flanges. 

These bolts when fitted in flange couplings and flange mounted propellers , have the advantage that they are easily removed for inspection and maintenance. Since the strain is calculated excessive stress is avoided.

Couplings becomes more rigid and thus less pron to fretting corrosion and fracture.