Compressed air; theory and computations . tio ofcompression. 16 COMPRESSED AIR Figure 5a illustrates one class of inlet valve with its operatingmechanism, the direction of motion being indicated by piston d is at the left end of its stroke with compressed airin the clearance. If the port of valve A opens at this instant, thecompressed air in the clearance will escape out into the inletpassage e. Evidently it is desirable to delay the opening of theport until the piston has receded enough to allow the air in theclearance to expand down to atmospheric pressure, thus lettingthe air in
Compressed air; theory and computations . tio ofcompression. 16 COMPRESSED AIR Figure 5a illustrates one class of inlet valve with its operatingmechanism, the direction of motion being indicated by piston d is at the left end of its stroke with compressed airin the clearance. If the port of valve A opens at this instant, thecompressed air in the clearance will escape out into the inletpassage e. Evidently it is desirable to delay the opening of theport until the piston has receded enough to allow the air in theclearance to expand down to atmospheric pressure, thus lettingthe air in the clearance give back the work done in compressingit. Evidently, the opening should not be delayed longer, forthere would result a suction (pressure below atmosphere) behindthe piston which would cause a loss of work. When the adjust-ment is correct, there is no puffing or spitting at the inlet the adjustments are not correct, an experienced operatorcan detect the fact by the noise made by air puffing out or intothe parts. ,. SECTION MN SECTION QR Fig. 5a. If the clearance and the ratio of compression are known, theerector or operator can adjust the valves correctly. For example,assume the clearance as 1 per cent., r = 7 and n = InTable I for r = 7, v2 -5- vi = or say Vi = 5v2, that is the clear-ance should expand to five times its volume before the port stated, the piston should move back 4 per cent, of itsstroke before the port opens. Thus, if the stroke be 18 in. thepiston should be moved back X 18 = (or say % in.)and while the piston stands in that position bring the edge ofvalve and edge of inlet port to coincide by turning the rod & or aas the case may be. The manufacturers always put marks onthe end of the valve and on the inclosing cylinder that will enablethe operator to make this adjustment. In order that one adjustment may not interfere with another,it is necessary that the valve B be adjusted first by rotating FORMUL
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