Electromagnetic clutches are used in a variety of mobile pump applications. They help reduce fuel consumption, assist with cold starts, reduce load on engines, and extend the life of the pump. They are commonly found on commercial fishing boats' hydraulic pumps, utility and service vehicles, tow trucks, mobile compressors, and water pumps, and more.

When sizing a clutch, the two most important selection criteria to prevent unwanted clutch slippage is speed and torque. Speed is important because the engagement energy is proportional to the square of the speed. The clutch engagement energy at 1,600 rpm is quadruple the energy at 800 rpm, even though the speed is double. Fundamentally, engagement energy is responsible for clutch slippage.

Torque is the other critical design criteria. Ogura rates the clutches for static torque, as do most clutch manufacturers. Static torque is a baseline, but it is related to torque transfer capability at zero rpm. When clutches engage dynamically, we must consider dynamic torque which is less than the static rating. Dynamic torque rating changes with engagement speed. For most applications operating within current industry norms, dynamic torque can drop to about 50-60% of rated static torque. If you engage it at higher speeds, the dynamic rating is decreased further.

Another consideration is torque spiking for the engine or pump. It is common that torque can spike so we need to consider a safety factor. Depending on the application, you may need to consider a safety factor of at least 2, but sometimes even much higher. Your torque calculation may reveal 375 lb-ft of torque required, but it is wiser to choose the 1,000 lb-ft rated clutch instead of the 400 lb-ft clutch to prevent slipping.

If torque required for the pump is unknown, there is a basic equation to use:

If pump efficiency is unknown, some make a general assumption of 85%.

Remember to consider dynamic torque and the safety factor for your equipment based on possible torque spikes.

Lastly, keep in mind that torque ratings are based on a properly burnished clutch. If you need to get full torque from a clutch, it needs to be burnished to achieve full torque transfer capability.

For smaller pumps and engines, the Ogura MA Series clutches are available in torques ranging from 58 to 175 lb. ft. For pumps requiring higher horsepower, the MMC Series are rated from 200 to 1500 lb. ft. A variety of bore sizes and pulley options are available from stock.

Benefits of using Ogura Mobile & General Purpose clutches:

• Long life
• Safety and convenience with remote starting
• Fuel and energy savings
• Built for outdoor operation
• Many years of proven success
• Custom designs available based on minimum order quantities
• Reduced engine load on cold weather starts
• Increased operational life of driven equipment
• Simple installation

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