PRESSURE REGULATORS OR RELIEF VALVES 



261 



cases, of course, some pressure rise occurs in the penstock. The 

 size of regulator depends largely upon the water velocity in the 

 penstock and upon the length of penstock between the turbine and 

 the forebay or between 

 the turbine and the surge 

 tank, if one is used. It is 

 usually attached directly 

 to the turbine casing and 

 discharges into the tail- 

 race, and the discharge 

 should not be connected 

 to the draft tube. 



Fig. 140 illustrates a 

 governor-operated pres- 

 sure regulator used with 

 reaction turbines. It is 

 mechanically connected to 

 the gate mechanism of the 

 turbine but the power re- 

 quired to operate it is sup- 

 plied by the pressure in 

 the penstock. No load is 

 imposed upon the gov- 

 ernor nor any pressure 

 drawn from the governor 

 system. The connection 

 to the turbine gate 

 mechanism simply oper- 

 ates the pilot valve of the 

 regulator which controls 

 its action. 



Fig. 141 shows another 

 type of governor-operated 

 relief valve, in which the 

 valve is interconnected 

 with the turbine gates 

 through a self-contained 



oil-pressure system, the operation of the relief valve being pro- 

 duced directly by the motion of the turbine gate. Above the 

 elbow forming the body of the relief valve casing will be noticed 



F'IG. 141. Governor-operated Relief Valve. 

 (I. P. Morris Company.) 



