Chapter 17. -COMPRESSED AIR PLANTS 



(^ 



^ 



TO OIL SPRAY FOR 

 TURBINE PINION 



OIL TO TURBINE" 

 PINION BEARING 



47.156 



Figure 17-8. — Lubrication system for turbine-driven high pressure air compressor. 



Automatic temperature shutdown devices are 

 fitted to all recent designs of high pressure air 

 compressors. Such a device stops the com- 

 pressor automatically (and does not allow it to 

 restart automatically) when the cooling water 

 temperature rises above a safe limit. Some com- 

 pressors are fitted with a device that shuts down 

 the compressor if the temperature of the air 

 leaving any stage exceeds a preset value. 



Control or regulating systems for naval air 

 compressors are mainly of the start- stop type. 

 With this type of control, the compressor starts 

 and stops automatically as the accumulator pres- 

 sure rises or falls to predetermined limits. On 

 electrically driven compressors, the system is 

 very simple: the accumulator pressure operates 

 against a pressure switch that opens when the 

 pressure upon it reaches a given limit and 

 closes when the pressure drops a predetermined 

 amount. On ■ steam-driven compressors, the 



accumulator pressure is piped to a control 

 valve (also called a pilot, trigger, or aux- 

 iliary valve) which, when the designed cutoff 



admits air to a plunger 



turbine governor valve. 



to be shut off and the 



When the pressure falls 



level, the control valve 



acting upon the plunger 



leakage or bleeding to at- 



steam is thereby permitted 



the governor valve and re- 



pressure is reached, 

 connected with the 

 This causes steam 

 compressor to stop, 

 to a predetermined 

 closes and the air 

 is released by 

 mosphere. The 

 to flow through 



start the turbine. 



Constant- speed control is a method of con- 

 trolling the pressure in the air accumulator by 

 controlling the output of the compressor without 

 stopping or changing the speed of the unit. This 

 type of control is used on compressors that have 

 a fairly constant demand for air, where frequent 

 stopping and starting is undesirable. 



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