Hydraulic Hose Sizing

Horsepower to Flow

First of all, we must determine fluid flow rate from the horsepower and pressure.

Horsepower = Pressure × Flow / 1714, or:

HP = PQ / 1714

Q = (HP * 1714) / P

Determine the flow rate of a 28 HP power unit delivering 3000 PSI:

28 = (3000 * Q) / 1714

Q = (28 * 1714) / 3000 = 15.997 GPM

Determine the flow rate of a 50 HP power unit delivering 3000 PSI:

50 = (3000 * Q) / 1714

Q = (50 * 1714) / 3000 = 28.5 GPM

Hose Sizing

These are the formulas and guidelines for determining sizes for the three hose types: Pressure, Return and Suction. They are determined from the fluid velocity in each type of hose. There are two sets of recognized values used are:

SAE Values

Pressure: 15 ft/sec

Return: 10 ft/sec

Suction: 4 ft/sec

NFP Association Values

Pressure: 20 ft/sec

Return: 15 ft/sec

Suction: 5 ft/sec

The more conservative SAE values are gaining acceptance in hydraulic designers. The formula for calculating the hose size is as follows:

V = Q / (3.117 * pi/4 * D ^ 2)

or

D = (Q / (3.117 * pi/4 * V) ) ^ 1/2

Where:

V is fluid velocity in ft/sec

Q is fluid volume in gallons/min

D is hose inside diameter in inches

Note: The sizing guidelines say to always round up.

Now, let's calculate the hose sizes:

Supply (Pressure) Hose

V = 20 ft/sec and Q is shown for 13, 16, and 28.5 GPM:

D = (13 GPM / (3.117 * pi/4 * 15 ft/sec) ) ^ 1/2 = 0.595 in

D = (16 GPM / (3.117 * pi/4 * 15 ft/sec) ) ^ 1/2 = 0.660 880

D = (28.5 GPM / (3.117 * pi/4 * 15 ft/sec) ) ^ 1/2 = 0.762 in

Return Hose

V = 15 ft/sec and Q is shown for 13, 16, and 28.5 GPM:

D = (13 GPM / (3.117 * pi/4 * 10 ft/sec) ) ^ 1/2 = 0.728 in

D = (16 GPM / (3.117 * pi/4 * 10 ft/sec) ) ^ 1/2 = 0.808 in

D = (28.5 GPM / (3.117 * pi/4 * 10 ft/sec) ) ^ 1/2 = 1.07 in

Suction Hose

V = 5 ft / sec and the Q is shown for 13, 16 and 28.5 GPM:

D = (13 GPM / (3.117 * pi/4 * 4 ft/sec) ) ^ 1/2 = 1.15 in

D = (16 GPM / (3.117 * pi/4 * 4 ft/sec) ) ^ 1/2 = 1.28 in

D = (28.5 GPM / (3.117 * pi/4 * 4 ft/sec) ) ^ 1/2 = 1.70 in

Pump Displacement (Cubic Inch Per Revolution, or CIPR)

Calculate the displacement for a fixed displacement as follows:

CIPR = Flow Rate (in GPM) × 231 x Pump Efficiency / Pump RPM, or:

CIPR = GPM × 231 * PE / RPM

Note: The generally accepted value for pump efficiency is 97%.

The 28 hp Briggs & Stratton engine HP is rated at 3600 RPM. With 97% pump efficiency, pump displacement is:

CIPR = 16 × 231 * 0.97 / 3200 = 1.12 in³ / Rev

The 28 hp Renault engine HP is rated at 3000 RPM. With 97% pump efficiency, pump displacement is:

CIPR = 16 × 231 * 0.97 / 3000 = 1.19 in³ / Rev

The 50 hp Briggs & Stratton engine HP is rated at 3000 RPM. With 97% pump efficiency, pump displacement is:

CIPR = 28.5 × 231 * 0.97 / 3000 = 2.12 in³ / Rev