SEA-WATER SYSTEM AT POINT WHITNEY SHELLFISH LABORATORY 



149 



base. A 12 by 12 mesh per inch Saran 

 phistic screen on wood frame was kept in 

 one of the slots at all times and the top 

 of the box sealed by a i/^-inch steel plate 



and neoprene gasket, bolted down with 24 

 %-inch bolts set in a steel frame cast in 

 the concrete (fig. 1) . Elimination of most 

 of the metal contact with sea water was 



Figure 1. — Construction detail of the suction screen box at Point Whitney Shellfish Laboratory of 

 the Washington State Department of Fisheries: 1, building wall; 2, suction-box wall; 3, steel 

 cover plate ; 4, gasket blanket ; 5, strong back ; 6, screens ; 7, 4-inch sea-water-intake line ; 

 8, 4-inch pump suction line ; 9, 4- by 4- by %-inch angle iron ; 10, studpost. 



finally achieved by placing a i/^-inch-thick 

 neoprene blanket between steel plate and 

 suction box top. Holes for probe switch 

 rod, primer pipe, and air cushion cham- 

 ber were closed by threaded washers 

 attached to black iron pipe nipples. In 

 practice this device has proven somewhat 

 troublesome to maintain, but has been val- 

 uable in providing combination screen and 

 settling basin to minimize the amount of 

 sand or other hard objects passing through 

 the hard-rubber-lined pump. Certain de- 

 sign modifications of this type of suction 

 box would eliminate features we have 

 found unsatisfactory and still retain the 

 basic advantages of the device. 



The most important modification would 

 be to change the relative position of box 

 inlet and outlets so that pump suction is 

 at least 12 inches below the bottom of the 



incoming sea-water suction line. At the 

 same time the volume of water retained in 

 the box above the pump suction should be 

 nearly equal to the volume of the sea-water 

 suction line lying above the level of half 

 tide. 



A source of difficulty has been mainte- 

 nance of adequate vacuum while the sys- 

 tem is on automatic operation, since po- 

 rous spots in the concrete and poor bond- 

 ing between anchoring ring and concrete 

 sometimes allowed air to leak into the box. 

 Box walls, therefore, must be of high and 

 uniform density and should be concrete 

 at least 10 inches thick. To reduce the 

 area that must be fitted with removable 

 gasket, the cover-plate opening should be 

 made only large enough to allow insertion 

 and removal of two screens. The cover- 

 plate anchoring ring should be fabricated 



