A Simple and Inexpensive Constant Rate Driver for Syringes Additions of small quantities of liquids a t constant rates is a difficult operation without the aid of a syringe driver, hut because of the cost of commercially available drivers, their use in smaU laboratories has been limited. The syringe driver described below can be constructed in a short time from readily available and inexpensive materials. The three components of the driver mechanism and a complete constant drive apparatus are illustrated below. Exact dimensions and materials should be chosen to suit the intended application. Stationary parts can be assembled on s. ring stand using standard clamps. (1) Slotted drive t d e : 7-in. metal tube ('la in. i. d.), 6 X '/sin. slot (cut with hacksaw or milled), connected to drive unit by heavy rubber tubing. (2) Threaded d~iverod: 7-in. length of threaded rod (16 turns/in.) or '/& threaded electrical tubing (27 turns/in.). ( 3 ) Driue pin: '/pin. length of steel rod soldered into hole at upper end
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( 4 ) Female threaded block: constructed by soldering a nut onto each end of a
%in. tube, fixed to stand. ( 5 ) Drive unU: standard variable speed stirrer motor with gear reduction unit.
(6) F~ictionclamp: prevents the syringe from gravity feeding, a. device similar to a spring type clothes pin is adequate. The driver operates in the fallowing manner. As the drive unit turns 1, 2 is also turned via application of torque to the drive pin. The slot and pin arrangement allows 2 to have both rotational and translational motion. The r o t & m of 2 causes it to screw into 3 ( b e d to stand) thereby depressing the syringe plunger. At the point where the drive pin emerges from the slot in 1torqne is no longer transferred to 2 and addition ceases. The syringe driver described above is easily adaptable for use with any type of syringe, can provide constant flow at virtually any desired rate depending on motor speed and gear ratio chosen, and by adjusting the height of 1 relative to the drive pin can be mechanically adjusted to stop feeding at any point during an addition.
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