Quantcast Figure 6-14.Hydraulic pressure regulator.

basic  operating  principles  of  all  regulators  are similar  to  the  one  illustrated  in  figure  6-14. A regulator is open when it is directing fluid under  pressure  into  the  system  (fig.  6-14,  view  A). In the closed position (fig. 6-14, view B), the fluid in the part of the system beyond the regulator is trapped at the desired pressure, and the fluid from the pump is bypassed into the return line and back to the reservoir. To prevent constant opening and closing  (chatter),  the  regulator  is  designed  to  open at  a  pressure  somewhat  lower  than  the  closing pressure. This difference is known as differential or operating range. For example, assume that a pressure  regulator  is  set  to  open  when  the  system pressure drops below 600 psi, and close when the pressure rises above 800 psi. The differential or operating range is 200 psi. Referring  to  figure  6-14,  assume  that  the piston has an area of 1 square inch, the pilot valve has  a  cross-sectional  area  of  one-fourth  square inch, and the piston spring provides 600 pounds of   force   pushing   the   piston   down.   When   the pressure in the system is less than 600 psi, fluid from the pump will enter the inlet port, flow to the  top  of  the  regulator,  and  then  to  the  pilot valve. When the pressure of the fluid at the inlet increases to the point where the force it creates against the front of the check valve exceeds the force created against the back of the check valve by system pressure and the check valve spring, the check valve opens. This allows fluid to flow into the  system  and  to  the  bottom  of  the  regulator against the piston. When the force created by the system pressure exceeds the force exerted by the spring,  the  piston  moves  up,  causing  the  pilot valve to unseat. Since the fluid will take the path of  least  resistance,  it  will  pass  through  the regulator  and  back  to  the  reservoir  through  the return line. When  the  fluid  from  the  pump  is  suddenly allowed a free path to return, the pressure on the input side of the check valve drops and the check valve  closes.  The  fluid  in  the  system  is  then trapped  under  pressure.  This  fluid  will  remain pressurized until a power unit is actuated, or until pressure  is  slowly  lost  through  normal  internal leakage within the system. When the system pressure decreases to a point slightly  below  600  psi,  the  spring  forces  the  piston down and closes the pilot valve. When the pilot valve  is  closed,  the  fluid  cannot  flow  directly  to the return line. This causes the pressure to increase in the line between the pump and the regulator. This pressure opens the check valve, causing the fluid to enter the system. In   summary,    when  the  system  pressure decreases a certain amount, the pressure regulator will open, sending fluid to the system. When the system  pressure  increases  sufficiently,  the regulator  will  close,  allowing  the  fluid  from  the pump to flow through the regulator and back to the reservoir. The pressure regulator takes the load off  of  the  pump  and  regulates  system  pressure. Figure 6-14.—Hydraulic pressure regulator. 6-10


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