

Reg. 587, Reg. 588
Longitudinal Bar Stays


The maximum working pressure for longitudinal bar stays
is to be calculated from the appropriate one of the
following two formulae:
WP= 
C 
1.28
(D  )²
N 
Equation
XII/21 
A 
WP= 
C x D_{1}² 
Equation XII/22 
A 
WP is working pressure in pounds per square inch,
D is diameter of stays over threads in inches,
D_{1} is diameter of body of stays at its smallest part in
inches,
N is the number of threads of stay per inch,
A is area in square inches supported by one stay.
C is values given in Table below:
TABLE
XII/5
Stress on Longitudinal Bar Stays 
Range of tensile strength
of bar

Value of C 
Tons per square inch

Pounds per square inch 
26/30 
7850 
28/32 
8640 
30/34 
9420 
32/36 
10200 
Where bar stays are fitted in vertical boilers, not less
than four bar stays shall be fitted to boilers of 4 feet
and over but under 5 feet in diameter; five bar stays
to boilers of 5 feet and over but under 6 feet in diameter;
six bar stays to boiler of 6 feet and over in diameter.
In no case, shall the diameter of the stay at any part
be less than 1 inch. Where joined stays are fitted, the
strength of the knuckle joint employed shall be at least
equal to the strength of the remainder of the bar stay. 
Reg. 588
Loads on Stay Tubes and Bar Stays
Stay tubes and bar stays shall be designed to carry
the whole load due to the pressure on the area to be
supported, the areas being calculated as follows:
a) 
For a stay tube within
the tube nest the net area to be supported shall
be the product of the horizontal and vertical pitches,
in inches, of the stay tubes less the area of the
tube holes embraced. Where the pitch of the stay
tubes is irregular the area shall be taken as the
square of the mean pitch of the stay tubes (i.e.,
the square of ¼ of the sum of the four sides,
of any quadrilateral bounded by four adjacent stay
tubes), less the area of the tube holes embraced. 
b) 
For a stay tube in the
boundary row, or for a bar stay, the net area to
be supported shall be the area, in square inches
enclosed by lines passing midway between the stay
and the adjacent points of support and by the boundary
margin (see Regulation 589), less the area of any
tubes or stays embraced. 
c) 
In the case of a bar
stay where there are no stay tubes in the tube nest
the area to be supported shall extend to the tangential
boundary of the tube nest.



