Hydraulic Gear Motors

Hydraulic gear motors convert hydraulic pressure and flow into torque and angular displacement, rotary mechanical power, applied to a load via the shaft. Hydraulic fluid is moved into the motor causing the matched gear set to rotate. One of the gears is connected to the motor output shaft so producing the rotary mechanical power.

Hydraulic gear motors can be supplied in single or bi-rotational formats and units are available with a comprehensive range of mounting flange and shaft options including specific designs to accommodate high radial loads.

A complete range of integrated relief valves and anti-cavitation valves to suit a wide range of applications are available as standard.

A variety of materials used within the construction process ensure suitability for a wide range of fluids and environments.

Now including the new range of cast iron hydraulic gear motors for applications requiring high pressures, optimal performance and endurance.

A special shaft seal to allow hydraulic gear motors to bear extreme over-pressures without damage or failure.

A complete range of reversible units and hydraulic gear motors compliment the range of hydraulic motors and pumps for all types of industrial process, heavy plant, agricultural and commercial equipment.

These are some of the criteria to consider when deciding which size gear motor is needed for an application.
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Fluid velocity:
Calculate the velocity (v) of a fluid in a pipe as follows:
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v = Q ÷ (6 • A [m/s])

Q = flow rate [litre/min]
A = inside area of pipe [cm²]

Absorbed flow rate:
Calculate flow rate (Q) as follows:
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Q = (V • n • 10 -3) ÷ hvol [litre/min]

V = displacement [cm³/rotation].
n = rotation speed [rotations per minute].
hvol = motor volumetric efficiency (take 0.95 as an indicative value for rotation speeds ranging between 1000 and 2000 rotations per minute).

Delivered torque:
Calculate necessary torque (M) of a motor subject to pressure differential between input and output as follows:

M = (V • Dp • hhm) ÷ 62,8 [Nm]

V = displacement [cm³/rotation].
Dp = pressure differential [bar].
hhm = hydromechanical efficiency (take 0.80 as indicative value under cold conditions and 0.85 under working conditions).

Delivered power:
Calculate hydraulic power (P), delivered by a motor subject to a pressure differential between input and output as follows:

P = (Q • Dp • htot) ÷ 600 [kW]

Q = flow rate [litre/min.].
Dp = pressure differential [bar].
htot = total motor efficiency (hhm • hvol).

Values for hvol and hhm (and consequently htot) depend on pressure differential between supply and delivery, rotation speed, fluid features (temperature and viscosity) and filtering degree.Contact jbj Techniques technical office, email: info@jbj.co.uk or telephone: +44 (0)1737 767493 for further details on efficiency. The proper values for flow rate, torque and supplied according to pressure differential, rotation speed and set test conditions, can be found via this link for the Performance Curve pages.

There are several factors that need to be known before a calculation can be used to decide the most suitable sized hydraulic gear motor for an application.

1) First of all find out if the required output torque from the hydraulic gear motor is starting torque or running torque. Not that either will effect the way you size the hydraulic gear motor, but it is worth remembering that starting torque is, in most instances, higher than running torque.

2) Required output speed from the hydraulic gear motor.

3) Available hydraulic oil pressure of the application hydraulic circuit.

4) Required output shaft, required mounting interface and required inlet and outlet porting, flanged or threaded.

5) Don’t forget the coupling from the hydraulic motor shaft to the driven shaft. jbj Techniques have a wide range of mechanical power transmission couplings to suit many applications. We would be happy to help.

An application requires an output torque of 50 Nm at a speed of 2000 rpm and the hydraulic oil pressure available is 150 bar.

Using formula:   Vm = (20 x p x T) ÷ DP

Vm = Hydraulic gear motor displacement in cc/rev.
T = Required output torque 50Nm.
ΔP = 150 bar.

Put the above information into the formula:
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Vm = (20 x 3.142 x 50) ÷ 150

Vm = 20.94 cc/rev.

The above figure gives you the theoretical required hydraulic motor displacement to meet the above requirements. However it does not take into account the hydraulic motors mechanical inefficiencies.

The nearest hydraulic motor to the above Vm displacement figure of 20.94 cc/rev would be the Marzocchi group 2 ALM2 size 30. This has a displacement of 21.1 cc/rev. Looking at the performance charts below for the size 30, the dotted lines, and the 2000 rpm line. Taking the vertical 2000 rpm line until it intersects the 150 bar dotted line, and then taking a straight horizontal line at the intersection point to the torque output figures on the right of the graph you will see that the actual output torque of the motor will be 45 Nm. Therefore this motor will not meet the requirements.

If we then look at the next size motor up the ALM2-34, this has a displacement of 23.7 cc/rev. Then looking at the performance chart for this size of motor, and carrying out the same procedure as we did for the ALM2-30 it can be seen that this motor will produce just over 50 Nm. This would then be the hydraulic gear motor most suitable for the job without unnecessarily over sizing the motor.

Overall physical size can often be an important consideration. Available flow to the gear motor from the system can determine whether a small motor at high pressure is used or a larger motor at low pressure. A larger motor at lower pressure will achieve longer life but a lack of space available may determine that a smaller motor is used.

Controlling the speed of the gear motor is another requirement depending on the application. Please contact jbj Techniques technical office for further details and help to choose the correct size gear motor for your application, email: info@jbj.co.uk or telephone: +44 (0)1737 767493

These performance charts above plus dimensions, flange, shaft and port details, ordering codes, installation and maintenance details can be found for the range of Marzocchi gear motors within these two technical specification catalogue links:
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‍www.jbj.co.uk/e-publications/ALM-series-gear-motors-from-jbj-Techniques-Limited/index.html
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and
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‍www.jbj.co.uk/e-publications/GHM-series-gear-motors-from-jbj-Techniques-Limited/index.html
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We hope that this is of help but feel free to contact the jbj Techniques technical office, email: info@jbj.co.uk or telephone: +44 (0)1737 767493 if you need assistance or have further questions.

An example of the use of a gear motor using fluid power from the hydraulic system of an agricultural machine, heavy plant industrial machine, off-shore marine vessel, heavy goods vehicle or public service vehicle to create rotary mechanical power. In this case to power three hydraulic gear pumps for additional hydraulic systems on the machine.

A range of couplings, bellhousings and power take-off units are also available from jbj Techniques as is the technical expertise and back-up, plus skilled machine shop services to supply drive line packages for a wide range of industrial, agricultural, heavy plant and marine applications.
Check the product list for full range of quality products for mechanical and fluid power.