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Types of Reciprocating Pumps

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each stroke displaces a definite quantity of liquid, regardless of the resistance against which the pump is operating. The standard way of designating the size of a reciprocating pump is by giving three dimensions, in the following order: 1.   The diameter of the steam piston 2.   The diameter of the pump plunger 3. The length of the stroke For example, a 12- by 11- by 18-inch-reciprocating pump has a steam piston 12 inches in diameter, a pump plunger 11 inches in diameter, and a stroke of 18 inches. The  designation  enables  you  to  tell  immediately whether the pump is a high-pressure or low-pressure pump. TYPES OF RECIPROCATING PUMPS. Reciprocating  pumps  are  usually  classified  as  follows: Direct acting or indirect acting Simplex (single) or duplex (double) Single  acting  or  double  acting High pressure or low pressure Vertical or horizontal The reciprocating pumps used by the Navy are usually  one  of  the  following  types-direct-acting, simplex,  double-acting,  or  vertical.  The  types  most often used are direct acting pumps. The pump shown in figure 6-12 is direct acting because the pump rod is a DIRECT extension of the piston rod; and, therefore, the piston in the power end is DIRECTLY connected to the plunger in the liquid end. In an indirect-acting pump, there is some intermediate mechanism between the  piston  and  pump  plunger.  The  intermediate mechanism may be a lever or a cam. This arrangement can be used to change the relative length of strokes of piston  and  plunger  or  to  vary  the  relative  speed between piston and plunger. Or the pump may use a rotating crankshaft, such as a chemical proportioning pump in a distilling unit. The diaphragm pump shown in figure 6-13 is a direct-acting reciprocating pump. It is commonly used by Utilitiesman to pump water from a ditch or sump. Diaphragm pumps use a flexible diaphragm to move the liquid. The prime mover is usually a small gasoline or diesel engine with an eccentric connecting rod  arrangement  that  converts  rotary  motion  to reciprocating  motion.  On  the  suction  stroke,  the Figure 6-12.—Reciprocating pump. diaphragm  is  drawn  upward  into  a  concave configuration.  This  movement  of  the  diaphragm results in a partial vacuum that causes the suction ball valve  to  unseat  (and  at  the  same  time  keeps  the discharge ball valve seated) and to admit the liquid to the  pump  cylinder.  On  the  discharge  stroke,  the diaphragm is pushed downward, forcing the trapped liquid out through the discharge valve. Thus the liquid is made to move by the reciprocating motion of a flexible  diaphragm. Since the diaphragm forms an almost perfect seal in  the  pump  cylinder  between  the  liquid  being  pumped and the rest of the pump and driving mechanism, there is some danger of liquid abrasion or corrosion of moving parts behind the diaphragm. For this reason, diaphragm pumps are especially reliable for pumping mud, slime, silt, and other wastes or heavy liquids containing debris, such as sticks, stones, or rags. Liquid strainers are fitted at the suction inlet to prevent large objects from fouling the suction and discharge valves or from damaging the diaphragm. You can use the diaphragm pump for dewatering trenches where sewer lines or waterlines are to be laid or for repairing breaks in waterlines or sewer lines. Two of the most popular types of diaphragm pumps are the mud hog (closed discharge) and the water hog (open discharge). The MUD HOG is for 6-13



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