156 



p. R. WALNE 



From the roof tanks the sea water is 

 distributed to all rooms by standard poly- 

 thene piping. Throughout the labora- 

 tories the flow is controlled by polythene 

 valves (Saunders Valves Co. Ltd., Cwm- 

 bran, Newport, Monmouthshire). These 

 valves, in which all parts in contact with 

 the liquid are of plastic, are diaphragm 

 valves which are closed by depressing the 

 diaphragm until contact is made with a 

 weir in the pipe line. In the laboratories, 

 a supply is piped to plastic-lined pillar 

 taps fitted with Saunders valves. Else- 

 wdiere the lines end in threaded Saunders 

 valves to which various pipe lines for dif- 

 ferent apparatus can be attached as 

 required. 



HEATED SEA-WATER SYSTEM 



This system feeds a supply of warmed 

 sea water into the tank room to stimulate 

 spaw^ning in oysters in the winter months. 

 It is the most elaborate part of the system 

 and is therefore described in some detail. 



The general layout is show^n diagram- 

 matically in figure 1. The water is heated 



Figure 1. — System for wanning flowing sea 

 water: A, storage tank; B, warming tank; C, 

 3-kw. Vitreosil-covered immersion lieater ; D, 

 thermostat in glass pocket controlling lieater ; 

 E, safety thermostat ; F, drain. 



in a fiberglass tank which stands along- 

 side, and is connected to, the storage tanks 

 in the roof. As its top is level with that 

 of the storage tanks no level-control valves 

 are required. The water is heated elec- 

 trically by three 3-kilowatt immersion 

 heaters wdiich are coated with fused silica 

 ( Vitreosil, Thermal Syndicate Ltd., Wall- 

 send-on-Tyne) . These heaters, which 

 stand vertically in the tank, are made so 

 that the heating element is in the bottom 17 

 inches of the heater. Because this part of 

 the heater must not be exposed to the air 

 when it is on, the inlet and outlet of the 

 tank are above this level, and in the event 

 of a pump failure or excessive drawing off 

 of water the heaters cannot become un- 

 covered. 



The heaters are controlled by bimetal 

 thermostats (Sunvic T. . S. 8, Associated 

 Electrical Industries, London) inserted 

 into a glass thermometer pocket fixed ver- 

 tically in the tank. To improve heat 

 transmission the pocket is filled wnth 

 a heat transfer oil. The thermostat, 

 which has a differential of 0.1° C, controls 

 the heater through a hot-wire vacuum re- 

 lay (Sunvic, Associated Electrical Indus- 

 tries, London) . The basic heating is done 

 by two heaters which are controlled by one 

 thermostat, while the final control is given 

 by a third heater controlled by its own 

 thermostat. This allows the system to op- 

 erate with 1, 2, or 3 heaters according 

 to the requirements of the laboratoiy and 

 the temperature of the incoming water, 

 and avoids the disturbance to the labora- 

 tory electrical supply which might be 

 caused by switching 9 kilowatts on and off. 

 It is necessary to stir the water either me- 

 chanically or with compressed air; other- 

 wise marked temperature stratification can 

 occur. 



As an additional safety measure, a ther- 

 mostat in which the contacts close with rise 

 of temperature is placed in a thermometer 

 pocket fixed horizontally in the side of 



