Question

For the system in question 2 what is the

(a) power loss (HP) across the relief valve assuming that the relief valve allows full pump flow of 15 GPM through it.

(b)An unloading valve is used instead of a pressure relief valve for directing the flow to the tank at a pump discharge pressure of 30psi. What is the power saving obtained when an unloading valve is used instead of a relief valve from question A in directing the pump flow to the tank?

For reference: Question 2 was:

A pressure relief valve contains a poppet with a 0.65 in² area on which system pressure acts. During assembly, a spring with a constant of 2000 lbf/in is installed in the valve to hold the poppet against its seat. The adjustment mechanism is then set so that the spring initially compresses 0.15 in from its free length condition. In order to pass full pump flow through the valve at the PRV pressure setting, the poppet must move 0.10 in from its fully close position. Determine the

a) Cracking Pressure (psi) [Answer was 461 psi]

b) Full pump flow pressure (PRV pressure setting) [Answer was 769 psi]

Answer 1

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For reference:

a) Determine the force exerted on the poppet when it is fully closed Here spring constant is k and spring deflection from its free end is S Substitute 2000 lb/in. for k and 0.15 in. for S in the above equation F (2000) (0.15) 300 lb In order to put the poppet on the verge of opening FPcracking Here the cracking pressure is Prncking and the area of the poppet is A Substitute 0.65 in.2 for A and 300 lb for F in the above equation (0.65) 00 Pcacking Penacking 462 psi Thus, the cracking pressure is 462 psi

b) Determine the force exerted on the poppet when it is fully flow F=kS Here spring constant is k and spring deflection from its free end is S Substitute 2000 lb/in. for k and 0.25 in. for S in the above equation F (2000) (0.25) -500 lb In order to put the poppet on the verge of opening F -Prll amp fow Here full pump flow pressure is and the area of the poppet is A Substitute 0.65 in.2 for A and 500 lb for F in the above equation 500 ull pump flow Pfull pump flow-76923 psi Thus, the full flow pressure is769.23 psi o(0.65)