About Central Boilers Board •Contents Chapter Wise • Contents Regulation WiseIndian Boilers Act 1923

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 D1² Equation XII/22 A

WP is working pressure in pounds per square inch,
D is diameter of stays over threads in inches,
D1 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.

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