What Size Electric Clutch Do You Need? Here's How to Decide

What Size Electric Clutch Do You Need? Here's How to Decide

Apr 2nd 2020

At Coastal Hydraulics, we regularly receive calls from people looking for a new clutch or who are experiencing issues with their current electric clutch. Take the following scenario, for example: you're out on your fishing boat having a smooth, productive day, when all of a sudden you begin hearing a loud noise coming from your clutch—you may even notice a burning smell.

So, how exactly do you know what size clutch you need as a replacement? If you're using a Gresen pump, chances are that the answer is pretty straightforward—there are a number of clutches designed specifically for this popular and common pump. Otherwise, how to choose a clutch comes down to a few important details about your hydraulic system components.

Not sure where to start?  Here are the factors we use to determine the right clutch size for our customers.

1. Horsepower (HP)

The first step in right-sizing a clutch is to determine the approximate hydraulic (fluid power) horsepower, or HP needed to drive your system's pump.  While some of our customers have this information readily available, a formula may be used to determine HP for those who do not.  Two important numbers are needed to complete the formula - the PSI (pressure in pounds per square inch) of the hydraulic pump and system, as well as the total flow of hydraulic fluid running through the system each minute, measured as "gallons per minute (GPM)." From there, the following formula can be used: 

HP = PSI x GPM / 1456.9 (1714 x 85% of pump efficiency)

In order to end up with the right reading, PSI & GPM numbers must be 100% accurate.

2. Torque (T)

In addition to horsepower (HP), the amount of torque needed for the clutch to transmit must also be identified before setting out to choose a product. Just as with HP, a simple formula can be used to calculate torque:

Torque (T) = HP x 5250 / RPM (rotations per minute of the engine)

This should be a breeze considering you've already identified the amount of HP needed to drive the pump; all you need to know is the RPM the pump will work at. Once you've run the numbers, you'll be ready to apply a K factor.

3. Service (K) Factor

Now that you've gotten your clutch torque figured out, it's important not to overlook the threat of slippage, which can result from pressure spikes and/or high RPM engagement.  This means adding in a "service factor," also commonly referred to as a "K-factor." At Coastal Hydraulics, we typically multiply torque value by a K-factor of 2, which accounts for variables such as slippage that can occur during performance.  If your torque value is 90.8, for example, we would multiply by the K-factor - in this case, 2 - for a final number of 180.6. Thus, we would end up recommending a 200 lb. ft. clutch under these circumstances.

4. Additional Pump Information

In situations that are less cut and dry, additional information about your pump may be needed to determine the right clutch size for your needs.  As an example, our team would ask if your pump is belt-driven or a direct drive off the boat's motor or engine. Pump mount style matters, too; is it an "A" style with two bolts, or a "C" style with two or four bolts? Identifying the shaft size on the pump can also be helpful, including the number of teeth if the pump has a spline shaft.

Why Right-size a Clutch?

So, we've explained how to ensure the clutch you end up with is the right size, but why exactly is it so important to not overlook this step? The answer comes down to the performance and longevity of both your clutch and your hydraulic system.  If the clutch you purchase doesn't have quite enough torque, for example, you may end up working it too hard and running into more problems down the road. Clutches are not designed to work harder than they're supposed to, which may end in premature failure rates. Right-sizing a clutch helps to ensure that slipping never becomes a problem, allowing you to focus on the task at hand without any distractions.

Looking for the right clutch to help you work more efficiently? Are you in need of a quick electric clutch replacement? Coastal Hydraulics has a wide variety of clutches for different work environments. If you would like to talk more or shop clutches, feel free to reach out to us at (603) 474-1914.