Piping Layouts

8/7/2019 Piping Layouts

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PIPING LAYOUTS

Piping systems are very important for modern life. Piping is used in petroleum, natural gas, clean or waste water transportation and heating systems in buildings.

Besides the pipes, valves are used to maintain proper flow and control of the liquids or gases. Fittings are used to join pipes together.

Fittings are often screwed together, but they may be welded or attached via flanges and bolts.


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Symbolic notation is used for pipes, valves and fittings. Two general system used for piping drawings are given below:

Figure 11. Scale layout ; used principally for large pipe, as in boiler and power-plant work where lengths are critical..

Figure 12. Diagrammatic system; used on small-scale drawings such as architectural plans, plant layout etc. , or on sketches.

Appendices 32-35 provides dimensions for standard fittings and valves. Appendix 42 provides standard symbols for piping and heating.


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GEARS

Gears are mechanical elements that transmit power and motion from one shaft to another. There are various types, but basic forms are as follows:

Spur gears; for transmitting power from one shaft to a parallel shaft (Fig. 1a) (Helical gears, which have helical teeth instead of straight in spur gears, are also widely

similar transmission)

Spur gear and rack; for changing rotary motion to linear motion (Fig. 1b)

Bevel gears; for shafts whose axes intersect (Fig. 1c)

Worm gears; for nonintersecting shafts at right angles to each other (Fig. 1d)


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The teeth of gears are projections designed to fit into the tooth spaces of the mating gear and contact mating teeth along a common line known as the "pressure line". common form for the tooth flank is the involute, and when it is made in this form the gears are known as "involute gears". The "pressure angle" determines the partithe flank will have. 14 1/2 and 20 degrees are two standardized pressure angles.

Working principle


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There is no relative motion. When two gears are in mesh, the smaller gear may be called the pinion P, leaving the larger gear to be called G.

where D is pitch diameter and n is revolutions per unit of time.


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Other letter symbols and formulas for calculation are as follows:

N, Number of teeth


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Pd, diametral pitch : number of teeth on the gear for each inch of pitch diameterPd=N / [D (in)]

m, module : metric gearing uses the module, m, instead of inch unit, diametral pitch. m = [D (mm)] / N

p, circular pitch : the length of the arc of the pitch diameter circle subtended by a tooth and a tooth space

pitch (in) = pitch (mm) =

Those module, m, or diametral pitch, Pd, values must be equal to each other for gears and pinions, that will be working together.

Therefore center distance =

a, addendum: radial distance between the pitch diameter circle and the top of a tooth = (for standard 14 1/2 and 20 deg involute) 1 / Pd

b, dedendum: radial distance between the pitch dia. circle and the bottom of a tooth = (for standard 14 1/2 and 20 deg involute) 1.157 / Pd

DO, outside diameter: diameter of the circle containing the top surfaces of the teeth, DO = D + 2a = (N + 2) / Pd

DR, root diameter: diameter of the circle containing the bottom surfaces of the tooth spaces, DR= D - 2b = (N - 2.314) / Pd


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CAMS

Cams are machine elements with surface or groove formed to produce a spherical or irregular motion to a second part called a follower.

The direction of motion of the follower with respect to the cam axis determines two general types of cams:

(1) radial or disc cams; in which the follower moves in a direction perpendicular to the cam axis (Fig. 13 a-b-c-d)

(2) cylindrical or end cams; in which the follower moves in a direction parallel to the cam axis. (Fig. 13 e-f)

Several types of cams are shown in Figure 13. (p. 546)

Follower types in Fig. 13a :

1- Knife edge

2- Flat surface

3- Roller type


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Cams can be designed to move the follower with constant velocity, acceleration, or harmonic motion. In many cases combinations of these motions, together with surf

for sudden rise or fall, or to hold follower stationary, make up the complete cam surface.

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Piping Layouts