# Common Calculations For Hydraulic Motors

Update:08-01-2019
Abst:

Sometimes it is very convenient to be able to calculate […]

Sometimes it is very convenient to be able to calculate the speed, torque and flow of the hydraulic motor. In this blog post, China Hydraulic Motors will show you some common hydraulic motor calculations and provide examples of how to use them.

the first thing

We use these symbols and units in our calculations:

⍵ is the hydraulic motor speed in rpm

D is the motor displacement per revolution in cubic inches

F is the flow rate in gpm

HP is horsepower

P is the pressure in psi

T is the torque in inches-pounds

Fortunately, you can do it with a simple calculator, including a calculator on your smartphone. Remember π= 3.14.

Calculate hydraulic motor speed

If you know the fluid motor displacement D in cubic inches and the flow rate F in gallons per minute, you can calculate the speed in rpm. This is the equation:

⍵= F x 231 / D.

For example, the flow rate F is 75 gpm, the displacement D is 11.3 cubic inches, and the hydraulic motor speed will be...

⍵= 75 x 231 / 11.3 = 1,533 rpm

Calculate hydraulic motor torque

There are different ways to calculate the torque of the hydraulic motor based on the value you know. The following are the most commonly used formulas.

Flow, pressure and speed

If your flow rate F is in gpm, the pressure P is in psi, and the speed is in twips, you can find the torque T in inches-pounds using the following formula:

T = F x P x 36.77 /⍵

If your flow rate F is 75 gallons per minute, the pressure P is 5,076 psi, and the speed ⍵ is 1,558 rpm, then the resulting torque T (inches - lbs) will be:

T = 76.1 × 5000 × 36.77 / 1500 = 9,193 inches - pound

Horsepower and speed

If your HP HP and hydraulic motor speed is ⍵rpm, you can find the torque T (inches - lbs) using the following formula:

T = HP x 63025 /⍵

If your hydraulic motor is 225 hp and the rpm is 1,500 rpm, the resulting torque will be...

T = 225 * 63025/1500 = 9,454 inches - pounds

Pressure and displacement

If your pressure P is in psi and the motor displacement D is in cubic inches, you can find the torque T in inches-pounds using the following formula:

T = P x D / (2xπ)

If the pressure P is 5,000 psi and the displacement D is 11.3 cubic inches, the resulting torque T will be...

T = 5000 × 11.3 / (2 × π) = 8,989 inches - pounds

Calculate hydraulic motor flow

If you also know the motor displacement D in cubic inches, you can determine the flow rate F (gallons per minute) required to reach a certain speed at ⍵ speed:

F = Dx⍵/ 231

If your displacement is 11.3 cubic inches and you need 1,500 rpm, then the flow rate needs

F = 11.3×1500/231 = 73.38gpm

Hydraulic motor calculations may seem a little daunting at first, but once you see the examples and you get the right data, these calculations are fairly straightforward.

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