Pitch pocket

Pitch pockets ordinarily have so little effect on structural lumber. However, the presence of a large number of pitch pockets may indicate shake or weakness of bond between annual rings. 

Dip-grained wood n. Wood, which has single waves or undulations of the fibers, such as occur around knots and pitch pockets. 

Pitch pocket n. An opening between the growth rings containing resin in certain softwoods. Syn resin pocket, pitch streak. 

Instantaneous surges of water under pressure caused by sudden interruptions in water flow in a pipe or water system, producing a hammering sound and leading to metal stress and possible eventual failure. Water hammer can develop where a steam main is incorrectly pitched, has un-drained pockets or where steam flows up and meets draining condensate flowing down causing a temporary interruption in both flows. 

This micro device consists of a square micro chamber which has as a bottom plate a conventional DNA micro-array chip sealed by a cover slip with double-sided adhesive tape (see Figure 1.26) [24], The adhesive tape serves as a spacing gasket to define the shape and dimensions of the chamber. The cover slip contains the air pockets with a uniform, pitched distribution. The air pockets trap the air bubbles... 

M 10] [M 11] [P 9] [P 10] Bubbles with radii of 0.5 mm can stir fluid volumes in a distance with a radius smaller than 2 mm [23, 24], Thus, any micro chamber is suitable for acoustic micro streaming with a depth < 2 mm and with an air pocket pitch < 4 mm. 

A — Concrete bottom of electrolyzer, B — Graphite anodes, C - Ijaver of lead in which the anodes are embedded, D — Protecting layer over the lead (made of cement and pitch), E — Copper conductor to anodes (embedded In the lead, F — Steel frame to which cathodes are wolded, (J — Hollow pocket cathodes (of steel netting), // — Copper conductor to cathode,... 

NIOSH. 2001. Coal tar pitch volatiles. NIOSH pocket guide to chemical hazards. Cincinnati, OH. National Institute for Occupational Safety and Health, http //www.cdc.gov/niosh/npg/npgd0145.html. September 17, 2001. 

In the recleaning of the heat exchanger, several of the parallel, return-bend U-tubes (1 inch in diameter) were purposely pitched to assure a long section (approximately 10 feet) of trapped sodium. As would be expected from the previous estimate of the diffusion coefficient for water through concentrated caustic, the humid gas was not effective in removing these sodium pockets. The humid gas did successfully reclean the balance of the heat-exchanger circuits. In this phase of the operation, the maximum temperature rise did not exceed 130 °F. 

Although the pockets of sodium were not removed from several of the pitched U-tubes, the 100% steam phase was followed by a boiling water rinse. The tubes were cleaned of the long sodium pocket although a localized temperature rise of approximately 900 °F. was experienced. This, of course, further demonstrates the desirability of complete drainability. It also indicates that with the bulk of the sodium area removed by the initial humid-gas procedure, boiling water can be added to a system containing an unreacted pocket with reasonable expectancy that serious overpressure will not occur. However, this technique would not be recommended if the sodium pocket was adjacent to thermal sensitive components. 

Pitch line clearance provides at least three benefits. It reduces the possibility of material being trapped in a tooth pocket it accommodates minor manufacturing inaccuracies and it reduces the possibility of certain malfunctions. Pitch line clearance reduces the effective pressure angle however, pitch line clearance of 10% of the chain pitch reduces the pressure angle by only 1 or 2 degrees. Pitch line clearance also reduces the tooth thickness, and too much pitch line clearance can seriously weaken the tooth. 

Pitch line clearance can create backlash between the chain rollers and sprocket teeth. The effect of backlash can be relieved by making the bottom diameter smaller than the root diameter. The difference in diameters must be enough that the roller entering the sprocket from the tight strand is on one side of the tooth pocket, while the roller entering from the slack strand is on the opposite side of the pocket. The position of the chain during backlash is shown in Figure 4-39. 

A drawing of the type A tooth form for standard flat-top chain is shown in Figure 4-42. Equations for computing the important dimensions are also shown in Figure 4-42. The tooth form is simply a pair of pocket radii connected at the bottom diameter by pitch line clearance. The height of the tooth must be cut off near the pitch diameter to clear the bottom surface of the top plates in the chain. 

Obstacle density is classified as low, medium, and hig as shown in Table 3.5, as a function of the blockage ratio and pitch. The blockage ratio is defined as the ratio of the area blocked by obstacles to the total cross-section area. The pitch is defined as the distance between successive obstacles or obstacle rows. There is normally an optimum value for the pitch when the pitch is too large, the wrinkles in the flame front wiU burn out and the flame front will slow down before the next obstacle is reached. When the pitch is too small, the gas pockets between successive obstacles are relatively unaffected by the flow (Baker et al., 1994). 

Very delicate products may be damaged in transit by the repetitive dynamic repose effect of the material sliding down the front of the advancing pocket of product moved forward in a pitch space. 

The volume of material that can be carried forward in the pitch space decreases with the change in geometry to determine the maximum level of the pocket of material that can be moved. 

Even if all stock components including broke were previously fine-screened, bundles and lumps can be aeated thereafter by deposition. Secondary stickies and pitch particles may also form in the paper machine system. Final screening is therefore done directly before the headbox with pressure saeens (see Section 4.2.3). In most cases the screen baskets are slotted. Due to their position in the process, the screens exhibit special characteristics, i. e. very low pulsation generation by using special rotary elements, polished surfaces to avoid deposits, high availability by simple design and special design to prevent air pockets [1]. 

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