Hyd. Pressure Relief ??

schmism · Nov 30, 2006

RickB said:
increases the spring rate; oil pressure has to overcome the spring to unseat the relief valve poppet.

generally you wouldnt change a spring rate. its a constant lbs/inch.

but if i understand right, adding shims would increase the PRELOAD on the valve, meaning you need more force on the other side (hydrolic pressure) to open the seat... (like you said)

is the hydrolic system of our tractors rated at 2000 rpm or at 540 speed?

is it regulated by the relef valve... so if we hit that pressure at 1800 rpm then addtional RPM dosnt mean addtional pressure....?

RickB · Nov 30, 2006

schmism said:
generally you wouldnt change a spring rate. its a constant lbs/inch.

but if i understand right, adding shims would increase the PRELOAD on the valve, meaning you need more force on the other side (hydrolic pressure) to open the seat... (like you said)

is the hydrolic system of our tractors rated at 2000 rpm or at 540 speed?

is it regulated by the relef valve... so if we hit that pressure at 1800 rpm then addtional RPM dosnt mean addtional pressure....?

OK, so spring rate was a poor choice of terminology. The point was shims need to be added to raise the relief pressure. Hydraulic flow is rated at a given engine speed where fixed displacement pumps are involved as in this case. I don't know at what speed the subject tractor is rated But the difference in flow between 2000 ERPM and 540 PTORPM won't be discerned by very many operators. Hydraulic pressure is determined by the relief valve setting AND THE DEMAND OF WHATEVER LOAD IS PLACED ON THE SYSTEM. Once the engine is throttled up to some point off low idle where relief pressure can be obtained the max pressure reading will only change slightly as the flow across the relief valve increases with the porportionally higher engine speed. Pressure and flow are entirely different critters.