252 HYDRAULIC EQUIPMENT 



used for very small units. In fact, they are being rapidly dis- 

 carded. 



A hydraulic pressure governor system can be divided in two 

 distinct parts the pumping outfit and the governor unit proper. 



The pumping outfit in its simplest form consists of a power 

 pump, a pressure tank, a receiving tank and suitable connecting 

 pipes, valves, gauges, etc. The fluid which is used to operate 

 the power cylinder of the governor is obtained from the pressure 

 tank, which normally should be about half filled and of sufficient 

 capacity to provide for a series of governor strokes, even though 

 the pump be temporarily inoperative. The receiving tank receives 

 the fluid after it has performed its work in the governor, the func- 

 tion of the pump being to draw the fluid from the receiving tank 

 and force it into the pressure tank together with a sufficient amount 

 of air to obtain a pressure of from 100 to 200 pounds per square 

 inch. This compressed air is the immediate source of energy for 

 operating the governor, and although the pump accumulates or 

 renews this energy at a comparatively slow rate, it is available 

 for use in the governor as rapidly as the requirements of regulation 

 demand. It is this principle which makes possible the rapid 

 movement of the gates, which is essential to close speed regu- 

 lation. 



Two general systems of pressure supply are in successful use, 

 one utilizing oil and the other water. Water is advantageous in 

 the case of large plants. High-speed, multi-stage centrifugal 

 pumps of relatively small size may be used, while for oil, plunger 

 or gear pumps are required. The cost of oil necessary for the 

 pressure system of a large plant is also an important item, but, on 

 the other hand, the wear on valves and valve sleeves, etc., is un- 

 questionably less with oil than with water. Each of these two 

 systems has its advantages and disadvantages which, should be 

 carefully considered in each installation. 



Water treated with a soluble oil may also be used as a gov- 

 ernor fluid. A small percentage of soluble oil will supply the 

 required lubricating qualities, and will prevent rusting or cor- 

 rosion. The use of this fluid, handled by centrifugal pumps, is 

 probably the best practice in the case of large stations. 



Many large plants are now equipped with central pressure 

 systems. The pumps are sometimes motor-driven with auto- 

 matic pressure control. Sometimes the motors are allowed to 



