Your browser is not supported

You are using a browser we do not support any longer. To continue visiting our website, please choose one of the following supported browsers.

Our global presence

Please select a business area and your country and language.


Not quite sure about what you are looking for?

Use the links below to jump directly to the most searched topics

How do you prevent grinder wheel burst in metalworking?

January 21, 2020

Grinders Safety Expert Corner Metalworking

Discover the overspeed shut-off safety system.

expert article - overspeed shut-off - overview

Grinders with an overspeed shut-off function increase operator safety by reducing the risk of accidents.

High power pneumatic grinders are widely used in the metalworking industries such as foundries, shipyards and heavy machinery fabrication. We know that safety is of utmost importance in these industries. The overspeed shut-off function, a feature available in certain high-power pneumatic grinders, greatly reduces the risk of the grinding wheel from accidentally overspeeding. This is vital, since an overspeed incident can result in a burst disc that can injure the operator – potentially fatally.

Overspeed shut-off: how does it work?

Powerful pneumatic grinders have a governor that regulates the air inlet as a function of the speed. When speed increases, the inlet gets smaller to limit it to the maximum speed defined for the tool. This mechanism is developed to work at a certain air pressure; if the air pressure increases significantly, the speed will become too high. This is where the overspeed protection comes in. See it in action:

1. Regular pressure operation

At the correct pressure, air travels from the air inlet through the motor to the exhaust, without any intervention from the shut-off mechanism. The tool can work at its full effect.

Shut-off system not activated – The air flow is continuous.

2. Overpressure operation

If pressure increases heavily and the wheel speed significantly exceeds the maximum speed defined for the tool, the centrifugal force will liberate a steel ball that will block the air inlet. This shuts off the air flow and the tool stops. This happens instantly, in a fraction of a second, before the grinding wheel has the time to reach a speed where it could burst and send fragments into the path of the operator or someone else.

expert article - overspeed closed

Shut-off system activated – The air flow is interrupted.

IMPORTANT: To restart the tool, you need to carry out maintenance; the steel ball has to be removed from the air flow and put back in its initial position. An actioned shut-off typically signals an abnormality with the air flow, so we highly recommend you perform airline diagnostics and investigate the root cause.

Pol-Dunoyer expert head-zoom

The overspeed shut-off is there to protect you as an extra security on powerful grinders. If it goes off, you need to investigate why and correct any malfunctions in your airline

Pol Dunoyer , Global Business Development Manager

The shut-off function design varies between products and it may be slightly different to the example presented above.