DESIGN METHODOLOGY OF A SPRING LOADED RELIEF VALVE

INTRODUCTION:
In this CASE STUDY, a spring loaded safety relief valve has been designed based on a given problem statement. The design procedure involves the following:
 Designing of the SPRING to be used
 Designing of the THREADED FASTENER to be used for joint
The spring loaded safety valve has been assumed to be an assembly consisting of a spring (to be designed). The assembly attached to a pipe joint using a flange. Based on the cracking pressure, the shape of the flange and the resulting no. of threaded fasteners have to be decided. Having decided the nature of the flange the dimensions of threaded joints must be decided.

PROBLEM STATEMENT:
A boiler safety relief valve, using a close coil helical spring is set to blow-off at a fluid pressure of 0.35 N/mm2. A suitable compression spring is required for the purpose. The valve diameter is 12.70 mm. Use a suitable spring constant. Maximum lift allowed is 5 mm and the initial compression in the spring is 10 mm. Maximum shear stress allowed for wire is limited as per the material of the wire. Find the necessary dimensions of the spring.
The given valve is vertically attached to the top of a boiler with the help of a flange coupling using a certain number of bolts. Based on the working stress being subjected to the coupling, determine the bolt dimensions required for keeping the valve seated.

GIVEN DATA AND ASSUMPTIONS MADE:
Depending on the application (steam boiler), the following data has been gathered:
 Material selected= Carbon steel
 C= 6
 τ= 294 MPa
 G= 80 kN/mm2
 Max. pressure= 0.35 N/mm2
 Valve dia=12.70 mm

Bolt material= ASTM A36 (σt= 450 MPa)
 F.O.S =8
CALCULATION FOR SPRING:

Given in attachment.