6

in SI units S = 0.002 X rpm X stroke where S = piston speed, ft/min (m/min) rpm = revolutions per minute stroke = stroke of pump, in (mm)

A steam pump must fill with liquid from the suction supply on each stroke, or it will not perform properly. If the pump runs too fast, the liquid cannot flow through the suction line, pump passageways, and valves fast enough to follow the piston. On the basis of experience and hydraulic formulas, maximum piston speeds that vary with the length of stroke and the liquid handled can be established.

Table 2 shows general averages of maximum speed ratings for pumps of specified stroke handling various liquids. Some pumps, by reason of exceptionally large valve areas or other design features, may be perfectly suitable for speeds higher than shown. From the table, it should be noted that piston speed should be reduced for viscous liquids. Unless the net positive suction head is proportionately high, viscous liquids will not follow the piston at high speeds because frictional resistance in suction lines and in the pump increases with viscosity and rate of flow. Pumps handling hot water are run more slowly to prevent boiling of the liquid as it flows into the low-pressure area behind the piston.

TABLE 2 Average maximum speed ratings

Piston speed, ft/min*

TABLE 2 Average maximum speed ratings

Piston speed, ft/min*

Stroke length, in*

Cold water; oil to 250 SSU

Oil, 250-500 SSU

Oil, 500-1000 SSU

Oil, 1000-2500 SSU

Oil, 2500-5000 SSU

Boiler feed 212°F (100°C)

Survival Treasure

Survival Treasure

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