318 Machine Drawing
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d:\N-Design\Des18-3.pm5
The details of a simple lever safety valve are shown in Fig. 18.36. In this, valve seat 2 is
screwed in the valve body 1. The spindle 6 and toggle 7 together keeps the valve 3 pressed against
the seat. The top of the valve body is closed with a cover 4 with the help of six studs 14. A cover
bush 5 is used to prevent the leakage through the central hole of the cover. A lever guide 9 is
screwed to the cover in order to restrict the lever movement. The weight 12 is attached to the
lever 10 by means of lever pin 13. The toggle is held in position by means of toggle pin 8. Fulcrum
pin 11 is used to connect the lever and the cover, to act as the fulcrum.
Exercise
The details of a lever safety valve are shown in Fig. 18.36. Assemble the details and draw,
(i) The sectional view from the front, and
(ii) The view from above.
18.4.10 Spring Loaded Relief Valve
Safety or relief valves are used as boiler mountings and they let off steam from inside the boiler
whenever the pressure exceeds the set value. Thus, these valves safe guard the boilers. The
pressure may be set by using a dead weight or a tension spring with tension adjustment
arrangement.
Figure 18.37 shows the details of a spring loaded relief valve in which a tension spring is
used to set a pre-determined value for the steam pressure in the boiler. Valve 3 is placed vertically
inside the valve body 1 and the valve seat is an integral part of the valve body, in the design
considered. Stem 6 is located in the valve, with pointed end entering into the valve. Flange 7 is
now placed over this assembly and fastened to the valve body by fulcrum bolt 4. Lever 2 is
attached to the fulcrum bolt by using the fulcrum pin 5 such that, the lever rests on the stem 6.
One end of the tension spring 8 is attached to the lever and the other end to the tension adjusting
bolt 9. The tension adjusting bolt is attached to a base and the spring tension can thus be adjusted
to any required value.
Exercise
Assemble the parts of a spring loaded relief valve, shown in Fig. 18.37 and draw the following
views:
(i) Sectional view from the front, and
(ii) View from the right.
18.4.11 Ramsbottom Safety Valve
It is a boiler mounting and a safety device which protects the boiler against building-up of excess
pressure. The spring used in the safety valve is set to act when the steam pressure exceeds the set
value and allows the steam to escape. Thus, only the permissible value of steam pressure is
allowed inside the boiler.
Figure 18.38 shows the details of Ramsbottom safety valve. It consists of housing 1 with
two valve chests. The valve seats 3 are screwed into the housing and valves 2 are located in the
valve seats. The eye bolt 8 is fastened to the bridge of the housing, by means of washer 9 and both
the nuts 10 and 11. Pivot 4 is pinned to the lever 5 and it is placed over the valves and held in
position by safety links 7 and spring 6. The safety links 7 are fixed at one end to the lever and
the other end to the eye bolt 8 by pins 12 and split pins 13. The required rigidity is provided to this
