The volume o£ water displaced by a maximum stroke o£ the 

 piston, 2SniAc, is 151 liters. The corresponding linear dis- 

 placement in the test section 2SjjiAc/A, is 2.44 meters. The 

 amplitude of the horizontal velocity is: 



General. 



U = ^ (-|) S = 2^J. (|_) cm/s . C17) 



m 



IV. CONSTRUCTION DETAILS 



The tunnel is constructed primarily of steel, aluminum, and Lucite, 

 with lesser amounts of polyvinyl chloride (PVC) and brass. Most of the 

 standing framework is of 4.76- by 50.8-millimeter (3/16 by 2 inches) 

 steel angle, with 4.76- by 63.5-millimeter (3/16 by 2 1/2 inches) angle 

 used in the columns under the cylinders and reservoirs. Lucite members 

 are regularly fused together with solvent. Removable sections are flanged 

 and bolted together with gasket seals. The Lucite test section rests on 

 a steel plate welded to steel angle stiffeners, but most metallic elements 

 are bolted together. The aluminum cylinders are bolted to a 12.7 milli- 

 meter-thick (1/2 inch) aluminum slab; the reservoirs are of PVC pipe and 

 glued to a 25.4-millimeter (1 inch) PVC slab base. 



2. Cylinders, Pistons, and Seals . 



Construction of the cylinders, a crucial element in the tunnel, was 

 the most difficult. After failing in attempts to machine PVC pipe, and 

 rejecting stainless steel pipe because of initial cost and reputation 

 for difficult working, the cylinders were machined from alijiminum pipe. 

 Blemishes ip the machining required hand-finishing, and variations in 

 the cross-sectional areas were contained to less than 3 parts in 10,000. 

 A final anodizing process to prevent corrosion roughened the surface 

 slightly; however, subsequent tests revealed no undue friction or leakage 

 between the cylinder walls and the piston seals. The cylinders are 

 stiffened with flanges. 



Each piston is machined from PVC, is 50.8 millimeters (2 inches) 

 thick, and has two recessions, one each around its upper and lower 

 perimeters. Rubber "U-ring" seals with cross sections like a square 

 bottom letter "U" fit into the recessions. One horn of each ring 

 presses against the piston and the other against the cylinder wall; 

 horns of each ring face away from the other ring. The rings may need 

 occasional replacement, but are inexpensive and readily available. The 

 pistons have bleeds by which the space beneath them and between the 

 seals can be kept free of air. 



