# Talk:50 hp Power Cube Calculations

Power in a hydraulic system is flow time pressure. Starting with a 50 HP engine and a 3000 psi system pressure, to find volume flow rate first convert horse power into ft lbs / sec and then in lb / sec: 50 HP * 550 = 2750 ft lb / sec = 330,000 in lb /sec. Now dividing power by pressure gives flow: 330,000 in lb / sec / 3000 lb / in² = 110 in³ / sec = 6600 in³ / min. If this is direct drive from the engine at 2700 RPM, we can compute the require displacement of the pump: 6600 in³/min / 2700 rev/min = 2.44 in³/rev. (This is based on engine revolutions.)

Alternatively, given the 1.84 CIPR, we can compute maximum system pressure: Pressure = Work / Disp. / RPM = 1,980,000 in.lb/min / 1.84 in³/rev / 2700 rev/min = 3985 lb/in².

If you already have decided on a system pressure of 3000 psi and acquired a pump with a 1.84 CIPR displacement, then you have a few options. First you can just run what you have which will give a large margin for error and also reduce fuel consumption. Alternatively, you can insert a gear or chain drive between the engine and pump to give a speed increase to the pump. To find the transmission ratio needed we divide the computed displacement based on engine speed by the actual pump displacement 2.44 / 1.84 = 1.32. I'd put a 10 tooth sprocket on the pump and a 13 on the engine to achieve this ratio, or maybe even a 12 to give some room for error.