Stroke pumps, adjustable

Plunger diameter, stroke length, and type of stroking speed adjustment can be chosen individually for each pumphead in the multiple pumphead metering pump system (81-83). 

Traditional Apparatus. As indicated earlier, liquid delivery systems for controlled rate addition of monomers and initiators have tended to rely upon constant speed piston pumps (19) in which volumetric control is achieved by manual adjustment of stroke length, and monitoring is by discharge from measuring cylinders. 

The use of traditional rod and piston pumps continues at many LNAPL recovery locations, particularly at refineries and distribution terminals. These units are usually powered by single-speed electric motors and have adjustable stroke lengths to control the pumping rate. When installed with the intakes set at the optimum pumping depth, they function fairly well. The primary advantage of rod and piston pumps is that the smooth slow stroke rate can pump mixtures of product and water without creating a significant emulsion. 

Reciprocating positive displacement pumps may have adjustment of the length or frequency of the stroke as another control feature. These may be solenoid or pneumatic devices that can be operated off a flow controller, as shown on Figure 3.21(d). 

Feed tank and metering pump the flow rate through such a pump can be controlled by a stroke adjusting mechanism or a variable speed drive acting on the stoke frequency. Control can be achieved by a fixed adjustment or through a flow meter. 

These pumps have the advantage of being able to pump solvent in unlimited quantities and are of use when long separations or preparative situations exist. Figure 19-16 shows a diagram of how one type functions. These pumps usually have a maximum operating pressure of 6,00 p.s.i.g. (42 MPa) and flow rates adjustable from 0.5 to 5.0 mL/min. The internal volumes are from 60-200 pL/stroke. 

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