If you dropped your ice cream cone on the ground and then picked it up within five seconds, some say it is still safe to eat. That's the five second rule. However, there is another rule that applies for mowers, specifically consumer mowers. The PTO clutch brake on mowers is a safety device and 5 seconds becomes a critical number.

As an industry, guidelines developed over the years to promote safe equipment operation. ANSI B71.1:2012 standard sub clause 22.2 was established. Concisely, it says that new machines are recommended to have a braking device that will help slow the rotating cutting blades to a stop within 5 seconds after the clutch is disengaged. More specifically, it says that it should stop within that time limit for at least the first five thousand cycles.

For commercial mowers, the guidelines are a little less stringent. For those, the seven second rule applies. Again, this is aimed at keeping the operator safe as the blades come to a stop. The ANSI B71.4 standard applies. These machines are typically used by turf care professionals and the machines and decks tend to be larger with higher inertia which leads to slightly longer stop times.

The Ogura PTO clutch brake serves two functions. First, when power is applied to the coil, it becomes an electromagnet and engages the clutch. The torque from the engine is transmitted to the clutch and pulley and it then turns the blades through a belt connection. When the power is removed from the clutch, the magnetic field collapses and leaf springs inside the clutch brake pull the clutch armature plate against the brake shroud. This results in braking torque. It is purely mechanical, steel on steel contact. Another engagement of the clutch compresses those leaf springs and creates an air gap between the armature and brake shroud, allowing free rotation while actively mowing.

Ogura GT series PTO clutch-brakes are made in a variety of configurations and typically mount on gas and diesel engines rated up to 40 HP. Bore sizes match the typical engine shaft sizes. Pulley sizes can vary based on machine requirements. Some have hub outputs to mount your own pulley, sprocket or coupling half. Clutch torque is rated up to 400 lb-ft on the larger units. These clutches typically operate on 12 or 24VDC.

Benefits of using an Ogura PTO clutch brake:

• Long life
• Safety
• Fuel and energy savings
• Built for outdoor operation
• Many years of proven success
• For use with operator presence controls
• Available with a soft start controller
• Custom designs available based on minimum order quantities

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