N2 Fitting and Machining Theory|Hands-On! 85


Te pipes to which the valves are bolted have matching holes. A gasket with matching holes is usually fitted between the mating faces to ensure a leak free joint. Te bolts used to bolt the flanges together do not have thread on the area near the head, the thread only starts in the area just where the nut and washers fit.


• Te hand wheel (Figure 6.1, number 1), when rotated clock-wise, closes off the flow and when rotated anti-clockwise allows increasing amounts of liquid or gas to flow freely.


• Te stem (Figure 6.1, number 10) joins the hand wheel and the wedge (Figure 6.1, number 12) at the base.


• Te gate valve makes use of a gland mounted at the throat of the housing to prevent leakage along the shaſt (Figure 6.1, number 10).


• Te gland has packing material (Figure 6.1, number 5) that can be compressed, causing it to expand and press more tightly on the centre shaſt by tightening the bolts of the gland should there be a leak in this area.


• The wedge section (Figure 6.1, number 12) can vary in shape and size depending on what substance the valve controls.


• Gate valves oſten have a parallel gate that opens and closes, especially in the case of water transfer. Tese parallel gates work best when they are either fully open or fully closed.


Tis type of valve is commonly found in large water pipe lines on gold mines and other industries where thousands of litres of water are moved every day.


Diaphragm type valves


Te valve, shown in Figure 6.2, has a flexible diaphragm that is pushed downwards by the spindle when the hand wheel is rotated clockwise. Te amount of fluid or gas passing through the valve would be reduced progressively as the diaphragm descends.


At the base of the spindle there is a bearing plate that allows the downward and rotating movement from the spindle to be carried over to the pin and form plate without allowing the twisting force to be carried over as it would deform the diaphragm.


handwheel


set screw


spindle bushing bearing


compressor pin bonnet


When this valve is partly closed there is less turbulence caused in the flow of fluid than in the case of a gate valve.


Tis type of valve is oſten found in chemical installations.


tube nut


diaphragm


valve body plastic-lined


diaphragm valve Figure 6.2 Diaphragm type valve rising stem


spindle (inside)


PTFE-faced diaphragm and elastomeric diaphragm use same compressor design


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