314 Machine Drawing
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d:\N-Design\Des18-3.pm5
valve. The spindle 3 is screwed from bottom of the cover 2 such that, the square end of the spindle
projects out through the cover. Studs 8 are screwed to the body and the spindle and cover assembly
is fastened to the body by nuts 10. Studs 9 are screwed to the cover and the gland 6 is inserted into
the cover and tightened by nuts 11. To prevent the leakage of water through the cover, packing
material is introduced between the cover and gland. Hand wheel 7 is located on the spindle such
that, the square hole in the hand wheel meshes with the square portion of spindle. The hand
wheel is fixed to the spindle by nut 11.
By operating the hand wheel, the spindle permits the valve to get lifted from the valve seat
and allows feed water to enter the boiler.
Exercise
Assemble the parts of the feed check valve, shown in Fig. 18.34 and draw, (i) sectional view from
the front, (ii) view from the right and (iii) view from above.
18.4.8 Pressure Relief Valve
This valve is used in a pipe line to relieve the excess pressure in the line and safeguard the
installation. The details of a pressure relief valve are shown in Fig. 18.35. The valve is connected
such that, the inlet of the fluid flow is attached to the port A and outlet to the port B. When the
line pressure goes beyond the set value, the fluid is let-off through the port C. The required line
pressure may be set by changing the spring pressure accordingly.
The valve member 2 is placed in the body through D and spring 11 is introduced into the
valve member. The sealed adapter 4 is then screwed into the body so that it touches the spring.
Whenever there is an increase in the line pressure, the valve member is lifted-off from its seat.
However, this lift may be adjusted by the adjusting screw 3 which reaches the valve member
through sealed adapter and spring. The washer 9 of correct thickness âtâ is used between the body
and the sealed adapter, not only to adjust the spring pressure but also to act as seal. To prevent
leakage of oil between the adjusting screw and the adapter, seal 10 is placed in the adapter. The
adjusting screw is locked in position by means of the lock-nut 12.
For the manual method of pressure relief, the following parts of the assembly are used: The
seal 10 is placed in the groove provided in the body through E. Control rod 7 is slipped through the
oil seal and the adapter 6 is screwed into the body at E. The position of the control rod may be
varied by the control screw 5 screwed through the adapter. Finally, the control knob 8 is screwed
onto the control screw and fixed to it by means of a pin.
When the knob is operated so that the control rod forces the valve member away from its
seat, the fluid passes through the port C. The washer 9 is placed between the body and the adapter
and it not only acts as an oil seal but also controls the travel of control rod. When the knob is
operated in the opposite direction, the valve member is returned to its seat by its spring pressure
and the control rod is returned by the influence of the oil pressure.
Exercise
Figure 18.35 shows the details of a pressure relief valve. Assemble the parts and draw to full size,
(i) the view from the front and (ii) sectional view from above.
